| Author | Tokens | Token Proportion | Commits | Commit Proportion |
|---|---|---|---|---|
| Darren Hart | 3038 | 27.28% | 37 | 14.29% |
| Ingo Molnar | 1952 | 17.53% | 17 | 6.56% |
| Peter Zijlstra | 1202 | 10.79% | 30 | 11.58% |
| Thomas Gleixner | 1128 | 10.13% | 54 | 20.85% |
| Arnd Bergmann | 775 | 6.96% | 2 | 0.77% |
| Davidlohr Bueso A | 529 | 4.75% | 9 | 3.47% |
| Pierre Peiffer | 299 | 2.68% | 3 | 1.16% |
| Jiri Slaby | 229 | 2.06% | 3 | 1.16% |
| Rusty Russell | 224 | 2.01% | 7 | 2.70% |
| Jamie Lokier | 192 | 1.72% | 3 | 1.16% |
| Mel Gorman | 158 | 1.42% | 3 | 1.16% |
| Linus Torvalds | 151 | 1.36% | 5 | 1.93% |
| Eric Dumazet | 119 | 1.07% | 1 | 0.39% |
| Heiko Carstens | 110 | 0.99% | 4 | 1.54% |
| Jakub Jelínek | 106 | 0.95% | 2 | 0.77% |
| Shawn Bohrer | 79 | 0.71% | 1 | 0.39% |
| Alexey Kuznetsov | 72 | 0.65% | 1 | 0.39% |
| Lai Jiangshan | 69 | 0.62% | 2 | 0.77% |
| Eric Sesterhenn / Snakebyte | 64 | 0.57% | 1 | 0.39% |
| Sebastian Andrzej Siewior | 62 | 0.56% | 2 | 0.77% |
| Martin Schwidefsky | 56 | 0.50% | 1 | 0.39% |
| Nico Pitre | 56 | 0.50% | 1 | 0.39% |
| Stephen Rothwell | 47 | 0.42% | 1 | 0.39% |
| Olof Johansson | 39 | 0.35% | 1 | 0.39% |
| Michel Lespinasse | 33 | 0.30% | 2 | 0.77% |
| Rasmus Villemoes | 29 | 0.26% | 1 | 0.39% |
| Andrew Morton | 29 | 0.26% | 3 | 1.16% |
| Andi Kleen | 29 | 0.26% | 1 | 0.39% |
| Nicholas Piggin | 27 | 0.24% | 1 | 0.39% |
| Kees Cook | 19 | 0.17% | 2 | 0.77% |
| Hugh Dickins | 19 | 0.17% | 2 | 0.77% |
| Namhyung Kim | 15 | 0.13% | 2 | 0.77% |
| Li Jinyue | 14 | 0.13% | 1 | 0.39% |
| Pavel Emelyanov | 13 | 0.12% | 1 | 0.39% |
| Kirill A. Shutemov | 12 | 0.11% | 1 | 0.39% |
| Oleg Nesterov | 10 | 0.09% | 2 | 0.77% |
| Brian Silverman | 10 | 0.09% | 1 | 0.39% |
| Vitaliy Ivanov | 9 | 0.08% | 1 | 0.39% |
| Mauro Carvalho Chehab | 8 | 0.07% | 1 | 0.39% |
| Lance Roy | 7 | 0.06% | 1 | 0.39% |
| Andrea Arcangeli | 7 | 0.06% | 1 | 0.39% |
| Al Viro | 6 | 0.05% | 3 | 1.16% |
| Zhang Yi | 6 | 0.05% | 1 | 0.39% |
| Steven Rostedt | 5 | 0.04% | 2 | 0.77% |
| Andreas Schwab | 4 | 0.04% | 1 | 0.39% |
| Jason Low | 4 | 0.04% | 1 | 0.39% |
| Jianyu Zhan | 4 | 0.04% | 1 | 0.39% |
| Waiman Long | 4 | 0.04% | 1 | 0.39% |
| Colin Cross | 4 | 0.04% | 1 | 0.39% |
| Catalin Marinas | 4 | 0.04% | 1 | 0.39% |
| Andrey Mirkin | 3 | 0.03% | 1 | 0.39% |
| David Howells | 3 | 0.03% | 2 | 0.77% |
| David S. Miller | 3 | 0.03% | 1 | 0.39% |
| Clark Williams | 3 | 0.03% | 1 | 0.39% |
| Benjamin Herrenschmidt | 3 | 0.03% | 2 | 0.77% |
| Arjan van de Ven | 3 | 0.03% | 1 | 0.39% |
| Jesper Juhl | 3 | 0.03% | 1 | 0.39% |
| Gustavo A. R. Silva | 2 | 0.02% | 1 | 0.39% |
| Viresh Kumar | 2 | 0.02% | 1 | 0.39% |
| Christoph Hellwig | 2 | 0.02% | 1 | 0.39% |
| Dominik Dingel | 2 | 0.02% | 1 | 0.39% |
| Mike Rapoport | 2 | 0.02% | 2 | 0.77% |
| Adrian Bunk | 2 | 0.02% | 1 | 0.39% |
| Motohiro Kosaki | 1 | 0.01% | 1 | 0.39% |
| Michael Kerrisk | 1 | 0.01% | 1 | 0.39% |
| Andrew Lutomirski | 1 | 0.01% | 1 | 0.39% |
| Fengguang Wu | 1 | 0.01% | 1 | 0.39% |
| Randy Dunlap | 1 | 0.01% | 1 | 0.39% |
| Paul Gortmaker | 1 | 0.01% | 1 | 0.39% |
| Vegard Nossum | 1 | 0.01% | 1 | 0.39% |
| Jann Horn | 1 | 0.01% | 1 | 0.39% |
| John Stultz | 1 | 0.01% | 1 | 0.39% |
| Yang Yang | 1 | 0.01% | 1 | 0.39% |
| Xunlei Pang | 1 | 0.01% | 1 | 0.39% |
| Burman Yan | 1 | 0.01% | 1 | 0.39% |
| Michal Hocko | 1 | 0.01% | 1 | 0.39% |
| Akinobu Mita | 1 | 0.01% | 1 | 0.39% |
| Mikael Pettersson | 1 | 0.01% | 1 | 0.39% |
| Serge E. Hallyn | 1 | 0.01% | 1 | 0.39% |
| Total | 11136 | 259 |
/* * Fast Userspace Mutexes (which I call "Futexes!"). * (C) Rusty Russell, IBM 2002 * * Generalized futexes, futex requeueing, misc fixes by Ingo Molnar * (C) Copyright 2003 Red Hat Inc, All Rights Reserved * * Removed page pinning, fix privately mapped COW pages and other cleanups * (C) Copyright 2003, 2004 Jamie Lokier * * Robust futex support started by Ingo Molnar * (C) Copyright 2006 Red Hat Inc, All Rights Reserved * Thanks to Thomas Gleixner for suggestions, analysis and fixes. * * PI-futex support started by Ingo Molnar and Thomas Gleixner * Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com> * Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com> * * PRIVATE futexes by Eric Dumazet * Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com> * * Requeue-PI support by Darren Hart <dvhltc@us.ibm.com> * Copyright (C) IBM Corporation, 2009 * Thanks to Thomas Gleixner for conceptual design and careful reviews. * * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly * enough at me, Linus for the original (flawed) idea, Matthew * Kirkwood for proof-of-concept implementation. * * "The futexes are also cursed." * "But they come in a choice of three flavours!" * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */ #include <linux/compat.h> #include <linux/slab.h> #include <linux/poll.h> #include <linux/fs.h> #include <linux/file.h> #include <linux/jhash.h> #include <linux/init.h> #include <linux/futex.h> #include <linux/mount.h> #include <linux/pagemap.h> #include <linux/syscalls.h> #include <linux/signal.h> #include <linux/export.h> #include <linux/magic.h> #include <linux/pid.h> #include <linux/nsproxy.h> #include <linux/ptrace.h> #include <linux/sched/rt.h> #include <linux/sched/wake_q.h> #include <linux/sched/mm.h> #include <linux/hugetlb.h> #include <linux/freezer.h> #include <linux/memblock.h> #include <linux/fault-inject.h> #include <asm/futex.h> #include "locking/rtmutex_common.h" /* * READ this before attempting to hack on futexes! * * Basic futex operation and ordering guarantees * ============================================= * * The waiter reads the futex value in user space and calls * futex_wait(). This function computes the hash bucket and acquires * the hash bucket lock. After that it reads the futex user space value * again and verifies that the data has not changed. If it has not changed * it enqueues itself into the hash bucket, releases the hash bucket lock * and schedules. * * The waker side modifies the user space value of the futex and calls * futex_wake(). This function computes the hash bucket and acquires the * hash bucket lock. Then it looks for waiters on that futex in the hash * bucket and wakes them. * * In futex wake up scenarios where no tasks are blocked on a futex, taking * the hb spinlock can be avoided and simply return. In order for this * optimization to work, ordering guarantees must exist so that the waiter * being added to the list is acknowledged when the list is concurrently being * checked by the waker, avoiding scenarios like the following: * * CPU 0 CPU 1 * val = *futex; * sys_futex(WAIT, futex, val); * futex_wait(futex, val); * uval = *futex; * *futex = newval; * sys_futex(WAKE, futex); * futex_wake(futex); * if (queue_empty()) * return; * if (uval == val) * lock(hash_bucket(futex)); * queue(); * unlock(hash_bucket(futex)); * schedule(); * * This would cause the waiter on CPU 0 to wait forever because it * missed the transition of the user space value from val to newval * and the waker did not find the waiter in the hash bucket queue. * * The correct serialization ensures that a waiter either observes * the changed user space value before blocking or is woken by a * concurrent waker: * * CPU 0 CPU 1 * val = *futex; * sys_futex(WAIT, futex, val); * futex_wait(futex, val); * * waiters++; (a) * smp_mb(); (A) <-- paired with -. * | * lock(hash_bucket(futex)); | * | * uval = *futex; | * | *futex = newval; * | sys_futex(WAKE, futex); * | futex_wake(futex); * | * `--------> smp_mb(); (B) * if (uval == val) * queue(); * unlock(hash_bucket(futex)); * schedule(); if (waiters) * lock(hash_bucket(futex)); * else wake_waiters(futex); * waiters--; (b) unlock(hash_bucket(futex)); * * Where (A) orders the waiters increment and the futex value read through * atomic operations (see hb_waiters_inc) and where (B) orders the write * to futex and the waiters read -- this is done by the barriers for both * shared and private futexes in get_futex_key_refs(). * * This yields the following case (where X:=waiters, Y:=futex): * * X = Y = 0 * * w[X]=1 w[Y]=1 * MB MB * r[Y]=y r[X]=x * * Which guarantees that x==0 && y==0 is impossible; which translates back into * the guarantee that we cannot both miss the futex variable change and the * enqueue. * * Note that a new waiter is accounted for in (a) even when it is possible that * the wait call can return error, in which case we backtrack from it in (b). * Refer to the comment in queue_lock(). * * Similarly, in order to account for waiters being requeued on another * address we always increment the waiters for the destination bucket before * acquiring the lock. It then decrements them again after releasing it - * the code that actually moves the futex(es) between hash buckets (requeue_futex) * will do the additional required waiter count housekeeping. This is done for * double_lock_hb() and double_unlock_hb(), respectively. */ #ifdef CONFIG_HAVE_FUTEX_CMPXCHG #define futex_cmpxchg_enabled 1 #else static int __read_mostly futex_cmpxchg_enabled; #endif /* * Futex flags used to encode options to functions and preserve them across * restarts. */ #ifdef CONFIG_MMU # define FLAGS_SHARED 0x01 #else /* * NOMMU does not have per process address space. Let the compiler optimize * code away. */ # define FLAGS_SHARED 0x00 #endif #define FLAGS_CLOCKRT 0x02 #define FLAGS_HAS_TIMEOUT 0x04 /* * Priority Inheritance state: */ struct futex_pi_state { /* * list of 'owned' pi_state instances - these have to be * cleaned up in do_exit() if the task exits prematurely: */ struct list_head list; /* * The PI object: */ struct rt_mutex pi_mutex; struct task_struct *owner; atomic_t refcount; union futex_key key; } __randomize_layout; /** * struct futex_q - The hashed futex queue entry, one per waiting task * @list: priority-sorted list of tasks waiting on this futex * @task: the task waiting on the futex * @lock_ptr: the hash bucket lock * @key: the key the futex is hashed on * @pi_state: optional priority inheritance state * @rt_waiter: rt_waiter storage for use with requeue_pi * @requeue_pi_key: the requeue_pi target futex key * @bitset: bitset for the optional bitmasked wakeup * * We use this hashed waitqueue, instead of a normal wait_queue_entry_t, so * we can wake only the relevant ones (hashed queues may be shared). * * A futex_q has a woken state, just like tasks have TASK_RUNNING. * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0. * The order of wakeup is always to make the first condition true, then * the second. * * PI futexes are typically woken before they are removed from the hash list via * the rt_mutex code. See unqueue_me_pi(). */ struct futex_q { struct plist_node list; struct task_struct *task; spinlock_t *lock_ptr; union futex_key key; struct futex_pi_state *pi_state; struct rt_mutex_waiter *rt_waiter; union futex_key *requeue_pi_key; u32 bitset; } __randomize_layout; static const struct futex_q futex_q_init = { /* list gets initialized in queue_me()*/ .key = FUTEX_KEY_INIT, .bitset = FUTEX_BITSET_MATCH_ANY }; /* * Hash buckets are shared by all the futex_keys that hash to the same * location. Each key may have multiple futex_q structures, one for each task * waiting on a futex. */ struct futex_hash_bucket { atomic_t waiters; spinlock_t lock; struct plist_head chain; } ____cacheline_aligned_in_smp; /* * The base of the bucket array and its size are always used together * (after initialization only in hash_futex()), so ensure that they * reside in the same cacheline. */ static struct { struct futex_hash_bucket *queues; unsigned long hashsize; } __futex_data __read_mostly __aligned(2*sizeof(long)); #define futex_queues (__futex_data.queues) #define futex_hashsize (__futex_data.hashsize) /* * Fault injections for futexes. */ #ifdef CONFIG_FAIL_FUTEX static struct { struct fault_attr attr; bool ignore_private; } fail_futex = { .attr = FAULT_ATTR_INITIALIZER, .ignore_private = false, }; static int __init setup_fail_futex(char *str) { return setup_fault_attr(&fail_futex.attr, str); } __setup("fail_futex=", setup_fail_futex); static bool should_fail_futex(bool fshared) { if (fail_futex.ignore_private && !fshared) return false; return should_fail(&fail_futex.attr, 1); } #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS static int __init fail_futex_debugfs(void) { umode_t mode = S_IFREG | S_IRUSR | S_IWUSR; struct dentry *dir; dir = fault_create_debugfs_attr("fail_futex", NULL, &fail_futex.attr); if (IS_ERR(dir)) return PTR_ERR(dir); if (!debugfs_create_bool("ignore-private", mode, dir, &fail_futex.ignore_private)) { debugfs_remove_recursive(dir); return -ENOMEM; } return 0; } late_initcall(fail_futex_debugfs); #endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */ #else static inline bool should_fail_futex(bool fshared) { return false; } #endif /* CONFIG_FAIL_FUTEX */ static inline void futex_get_mm(union futex_key *key) { mmgrab(key->private.mm); /* * Ensure futex_get_mm() implies a full barrier such that * get_futex_key() implies a full barrier. This is relied upon * as smp_mb(); (B), see the ordering comment above. */ smp_mb__after_atomic(); } /* * Reflects a new waiter being added to the waitqueue. */ static inline void hb_waiters_inc(struct futex_hash_bucket *hb) { #ifdef CONFIG_SMP atomic_inc(&hb->waiters); /* * Full barrier (A), see the ordering comment above. */ smp_mb__after_atomic(); #endif } /* * Reflects a waiter being removed from the waitqueue by wakeup * paths. */ static inline void hb_waiters_dec(struct futex_hash_bucket *hb) { #ifdef CONFIG_SMP atomic_dec(&hb->waiters); #endif } static inline int hb_waiters_pending(struct futex_hash_bucket *hb) { #ifdef CONFIG_SMP return atomic_read(&hb->waiters); #else return 1; #endif } /** * hash_futex - Return the hash bucket in the global hash * @key: Pointer to the futex key for which the hash is calculated * * We hash on the keys returned from get_futex_key (see below) and return the * corresponding hash bucket in the global hash. */ static struct futex_hash_bucket *hash_futex(union futex_key *key) { u32 hash = jhash2((u32*)&key->both.word, (sizeof(key->both.word)+sizeof(key->both.ptr))/4, key->both.offset); return &futex_queues[hash & (futex_hashsize - 1)]; } /** * match_futex - Check whether two futex keys are equal * @key1: Pointer to key1 * @key2: Pointer to key2 * * Return 1 if two futex_keys are equal, 0 otherwise. */ static inline int match_futex(union futex_key *key1, union futex_key *key2) { return (key1 && key2 && key1->both.word == key2->both.word && key1->both.ptr == key2->both.ptr && key1->both.offset == key2->both.offset); } /* * Take a reference to the resource addressed by a key. * Can be called while holding spinlocks. * */ static void get_futex_key_refs(union futex_key *key) { if (!key->both.ptr) return; /* * On MMU less systems futexes are always "private" as there is no per * process address space. We need the smp wmb nevertheless - yes, * arch/blackfin has MMU less SMP ... */ if (!IS_ENABLED(CONFIG_MMU)) { smp_mb(); /* explicit smp_mb(); (B) */ return; } switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) { case FUT_OFF_INODE: ihold(key->shared.inode); /* implies smp_mb(); (B) */ break; case FUT_OFF_MMSHARED: futex_get_mm(key); /* implies smp_mb(); (B) */ break; default: /* * Private futexes do not hold reference on an inode or * mm, therefore the only purpose of calling get_futex_key_refs * is because we need the barrier for the lockless waiter check. */ smp_mb(); /* explicit smp_mb(); (B) */ } } /* * Drop a reference to the resource addressed by a key. * The hash bucket spinlock must not be held. This is * a no-op for private futexes, see comment in the get * counterpart. */ static void drop_futex_key_refs(union futex_key *key) { if (!key->both.ptr) { /* If we're here then we tried to put a key we failed to get */ WARN_ON_ONCE(1); return; } if (!IS_ENABLED(CONFIG_MMU)) return; switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) { case FUT_OFF_INODE: iput(key->shared.inode); break; case FUT_OFF_MMSHARED: mmdrop(key->private.mm); break; } } enum futex_access { FUTEX_READ, FUTEX_WRITE }; /** * get_futex_key() - Get parameters which are the keys for a futex * @uaddr: virtual address of the futex * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED * @key: address where result is stored. * @rw: mapping needs to be read/write (values: FUTEX_READ, * FUTEX_WRITE) * * Return: a negative error code or 0 * * The key words are stored in @key on success. * * For shared mappings, it's (page->index, file_inode(vma->vm_file), * offset_within_page). For private mappings, it's (uaddr, current->mm). * We can usually work out the index without swapping in the page. * * lock_page() might sleep, the caller should not hold a spinlock. */ static int get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, enum futex_access rw) { unsigned long address = (unsigned long)uaddr; struct mm_struct *mm = current->mm; struct page *page, *tail; struct address_space *mapping; int err, ro = 0; /* * The futex address must be "naturally" aligned. */ key->both.offset = address % PAGE_SIZE; if (unlikely((address % sizeof(u32)) != 0)) return -EINVAL; address -= key->both.offset; if (unlikely(!access_ok(uaddr, sizeof(u32)))) return -EFAULT; if (unlikely(should_fail_futex(fshared))) return -EFAULT; /* * PROCESS_PRIVATE futexes are fast. * As the mm cannot disappear under us and the 'key' only needs * virtual address, we dont even have to find the underlying vma. * Note : We do have to check 'uaddr' is a valid user address, * but access_ok() should be faster than find_vma() */ if (!fshared) { key->private.mm = mm; key->private.address = address; get_futex_key_refs(key); /* implies smp_mb(); (B) */ return 0; } again: /* Ignore any VERIFY_READ mapping (futex common case) */ if (unlikely(should_fail_futex(fshared))) return -EFAULT; err = get_user_pages_fast(address, 1, 1, &page); /* * If write access is not required (eg. FUTEX_WAIT), try * and get read-only access. */ if (err == -EFAULT && rw == FUTEX_READ) { err = get_user_pages_fast(address, 1, 0, &page); ro = 1; } if (err < 0) return err; else err = 0; /* * The treatment of mapping from this point on is critical. The page * lock protects many things but in this context the page lock * stabilizes mapping, prevents inode freeing in the shared * file-backed region case and guards against movement to swap cache. * * Strictly speaking the page lock is not needed in all cases being * considered here and page lock forces unnecessarily serialization * From this point on, mapping will be re-verified if necessary and * page lock will be acquired only if it is unavoidable * * Mapping checks require the head page for any compound page so the * head page and mapping is looked up now. For anonymous pages, it * does not matter if the page splits in the future as the key is * based on the address. For filesystem-backed pages, the tail is * required as the index of the page determines the key. For * base pages, there is no tail page and tail == page. */ tail = page; page = compound_head(page); mapping = READ_ONCE(page->mapping); /* * If page->mapping is NULL, then it cannot be a PageAnon * page; but it might be the ZERO_PAGE or in the gate area or * in a special mapping (all cases which we are happy to fail); * or it may have been a good file page when get_user_pages_fast * found it, but truncated or holepunched or subjected to * invalidate_complete_page2 before we got the page lock (also * cases which we are happy to fail). And we hold a reference, * so refcount care in invalidate_complete_page's remove_mapping * prevents drop_caches from setting mapping to NULL beneath us. * * The case we do have to guard against is when memory pressure made * shmem_writepage move it from filecache to swapcache beneath us: * an unlikely race, but we do need to retry for page->mapping. */ if (unlikely(!mapping)) { int shmem_swizzled; /* * Page lock is required to identify which special case above * applies. If this is really a shmem page then the page lock * will prevent unexpected transitions. */ lock_page(page); shmem_swizzled = PageSwapCache(page) || page->mapping; unlock_page(page); put_page(page); if (shmem_swizzled) goto again; return -EFAULT; } /* * Private mappings are handled in a simple way. * * If the futex key is stored on an anonymous page, then the associated * object is the mm which is implicitly pinned by the calling process. * * NOTE: When userspace waits on a MAP_SHARED mapping, even if * it's a read-only handle, it's expected that futexes attach to * the object not the particular process. */ if (PageAnon(page)) { /* * A RO anonymous page will never change and thus doesn't make * sense for futex operations. */ if (unlikely(should_fail_futex(fshared)) || ro) { err = -EFAULT; goto out; } key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */ key->private.mm = mm; key->private.address = address; get_futex_key_refs(key); /* implies smp_mb(); (B) */ } else { struct inode *inode; /* * The associated futex object in this case is the inode and * the page->mapping must be traversed. Ordinarily this should * be stabilised under page lock but it's not strictly * necessary in this case as we just want to pin the inode, not * update the radix tree or anything like that. * * The RCU read lock is taken as the inode is finally freed * under RCU. If the mapping still matches expectations then the * mapping->host can be safely accessed as being a valid inode. */ rcu_read_lock(); if (READ_ONCE(page->mapping) != mapping) { rcu_read_unlock(); put_page(page); goto again; } inode = READ_ONCE(mapping->host); if (!inode) { rcu_read_unlock(); put_page(page); goto again; } /* * Take a reference unless it is about to be freed. Previously * this reference was taken by ihold under the page lock * pinning the inode in place so i_lock was unnecessary. The * only way for this check to fail is if the inode was * truncated in parallel which is almost certainly an * application bug. In such a case, just retry. * * We are not calling into get_futex_key_refs() in file-backed * cases, therefore a successful atomic_inc return below will * guarantee that get_futex_key() will still imply smp_mb(); (B). */ if (!atomic_inc_not_zero(&inode->i_count)) { rcu_read_unlock(); put_page(page); goto again; } /* Should be impossible but lets be paranoid for now */ if (WARN_ON_ONCE(inode->i_mapping != mapping)) { err = -EFAULT; rcu_read_unlock(); iput(inode); goto out; } key->both.offset |= FUT_OFF_INODE; /* inode-based key */ key->shared.inode = inode; key->shared.pgoff = basepage_index(tail); rcu_read_unlock(); } out: put_page(page); return err; } static inline void put_futex_key(union futex_key *key) { drop_futex_key_refs(key); } /** * fault_in_user_writeable() - Fault in user address and verify RW access * @uaddr: pointer to faulting user space address * * Slow path to fixup the fault we just took in the atomic write * access to @uaddr. * * We have no generic implementation of a non-destructive write to the * user address. We know that we faulted in the atomic pagefault * disabled section so we can as well avoid the #PF overhead by * calling get_user_pages() right away. */ static int fault_in_user_writeable(u32 __user *uaddr) { struct mm_struct *mm = current->mm; int ret; down_read(&mm->mmap_sem); ret = fixup_user_fault(current, mm, (unsigned long)uaddr, FAULT_FLAG_WRITE, NULL); up_read(&mm->mmap_sem); return ret < 0 ? ret : 0; } /** * futex_top_waiter() - Return the highest priority waiter on a futex * @hb: the hash bucket the futex_q's reside in * @key: the futex key (to distinguish it from other futex futex_q's) * * Must be called with the hb lock held. */ static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb, union futex_key *key) { struct futex_q *this; plist_for_each_entry(this, &hb->chain, list) { if (match_futex(&this->key, key)) return this; } return NULL; } static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr, u32 uval, u32 newval) { int ret; pagefault_disable(); ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval); pagefault_enable(); return ret; } static int get_futex_value_locked(u32 *dest, u32 __user *from) { int ret; pagefault_disable(); ret = __get_user(*dest, from); pagefault_enable(); return ret ? -EFAULT : 0; } /* * PI code: */ static int refill_pi_state_cache(void) { struct futex_pi_state *pi_state; if (likely(current->pi_state_cache)) return 0; pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL); if (!pi_state) return -ENOMEM; INIT_LIST_HEAD(&pi_state->list); /* pi_mutex gets initialized later */ pi_state->owner = NULL; atomic_set(&pi_state->refcount, 1); pi_state->key = FUTEX_KEY_INIT; current->pi_state_cache = pi_state; return 0; } static struct futex_pi_state *alloc_pi_state(void) { struct futex_pi_state *pi_state = current->pi_state_cache; WARN_ON(!pi_state); current->pi_state_cache = NULL; return pi_state; } static void get_pi_state(struct futex_pi_state *pi_state) { WARN_ON_ONCE(!atomic_inc_not_zero(&pi_state->refcount)); } /* * Drops a reference to the pi_state object and frees or caches it * when the last reference is gone. */ static void put_pi_state(struct futex_pi_state *pi_state) { if (!pi_state) return; if (!atomic_dec_and_test(&pi_state->refcount)) return; /* * If pi_state->owner is NULL, the owner is most probably dying * and has cleaned up the pi_state already */ if (pi_state->owner) { struct task_struct *owner; raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); owner = pi_state->owner; if (owner) { raw_spin_lock(&owner->pi_lock); list_del_init(&pi_state->list); raw_spin_unlock(&owner->pi_lock); } rt_mutex_proxy_unlock(&pi_state->pi_mutex, owner); raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); } if (current->pi_state_cache) { kfree(pi_state); } else { /* * pi_state->list is already empty. * clear pi_state->owner. * refcount is at 0 - put it back to 1. */ pi_state->owner = NULL; atomic_set(&pi_state->refcount, 1); current->pi_state_cache = pi_state; } } #ifdef CONFIG_FUTEX_PI /* * This task is holding PI mutexes at exit time => bad. * Kernel cleans up PI-state, but userspace is likely hosed. * (Robust-futex cleanup is separate and might save the day for userspace.) */ void exit_pi_state_list(struct task_struct *curr) { struct list_head *next, *head = &curr->pi_state_list; struct futex_pi_state *pi_state; struct futex_hash_bucket *hb; union futex_key key = FUTEX_KEY_INIT; if (!futex_cmpxchg_enabled) return; /* * We are a ZOMBIE and nobody can enqueue itself on * pi_state_list anymore, but we have to be careful * versus waiters unqueueing themselves: */ raw_spin_lock_irq(&curr->pi_lock); while (!list_empty(head)) { next = head->next; pi_state = list_entry(next, struct futex_pi_state, list); key = pi_state->key; hb = hash_futex(&key); /* * We can race against put_pi_state() removing itself from the * list (a waiter going away). put_pi_state() will first * decrement the reference count and then modify the list, so * its possible to see the list entry but fail this reference * acquire. * * In that case; drop the locks to let put_pi_state() make * progress and retry the loop. */ if (!atomic_inc_not_zero(&pi_state->refcount)) { raw_spin_unlock_irq(&curr->pi_lock); cpu_relax(); raw_spin_lock_irq(&curr->pi_lock); continue; } raw_spin_unlock_irq(&curr->pi_lock); spin_lock(&hb->lock); raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); raw_spin_lock(&curr->pi_lock); /* * We dropped the pi-lock, so re-check whether this * task still owns the PI-state: */ if (head->next != next) { /* retain curr->pi_lock for the loop invariant */ raw_spin_unlock(&pi_state->pi_mutex.wait_lock); spin_unlock(&hb->lock); put_pi_state(pi_state); continue; } WARN_ON(pi_state->owner != curr); WARN_ON(list_empty(&pi_state->list)); list_del_init(&pi_state->list); pi_state->owner = NULL; raw_spin_unlock(&curr->pi_lock); raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); spin_unlock(&hb->lock); rt_mutex_futex_unlock(&pi_state->pi_mutex); put_pi_state(pi_state); raw_spin_lock_irq(&curr->pi_lock); } raw_spin_unlock_irq(&curr->pi_lock); } #endif /* * We need to check the following states: * * Waiter | pi_state | pi->owner | uTID | uODIED | ? * * [1] NULL | --- | --- | 0 | 0/1 | Valid * [2] NULL | --- | --- | >0 | 0/1 | Valid * * [3] Found | NULL | -- | Any | 0/1 | Invalid * * [4] Found | Found | NULL | 0 | 1 | Valid * [5] Found | Found | NULL | >0 | 1 | Invalid * * [6] Found | Found | task | 0 | 1 | Valid * * [7] Found | Found | NULL | Any | 0 | Invalid * * [8] Found | Found | task | ==taskTID | 0/1 | Valid * [9] Found | Found | task | 0 | 0 | Invalid * [10] Found | Found | task | !=taskTID | 0/1 | Invalid * * [1] Indicates that the kernel can acquire the futex atomically. We * came came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit. * * [2] Valid, if TID does not belong to a kernel thread. If no matching * thread is found then it indicates that the owner TID has died. * * [3] Invalid. The waiter is queued on a non PI futex * * [4] Valid state after exit_robust_list(), which sets the user space * value to FUTEX_WAITERS | FUTEX_OWNER_DIED. * * [5] The user space value got manipulated between exit_robust_list() * and exit_pi_state_list() * * [6] Valid state after exit_pi_state_list() which sets the new owner in * the pi_state but cannot access the user space value. * * [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set. * * [8] Owner and user space value match * * [9] There is no transient state which sets the user space TID to 0 * except exit_robust_list(), but this is indicated by the * FUTEX_OWNER_DIED bit. See [4] * * [10] There is no transient state which leaves owner and user space * TID out of sync. * * * Serialization and lifetime rules: * * hb->lock: * * hb -> futex_q, relation * futex_q -> pi_state, relation * * (cannot be raw because hb can contain arbitrary amount * of futex_q's) * * pi_mutex->wait_lock: * * {uval, pi_state} * * (and pi_mutex 'obviously') * * p->pi_lock: * * p->pi_state_list -> pi_state->list, relation * * pi_state->refcount: * * pi_state lifetime * * * Lock order: * * hb->lock * pi_mutex->wait_lock * p->pi_lock * */ /* * Validate that the existing waiter has a pi_state and sanity check * the pi_state against the user space value. If correct, attach to * it. */ static int attach_to_pi_state(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state, struct futex_pi_state **ps) { pid_t pid = uval & FUTEX_TID_MASK; u32 uval2; int ret; /* * Userspace might have messed up non-PI and PI futexes [3] */ if (unlikely(!pi_state)) return -EINVAL; /* * We get here with hb->lock held, and having found a * futex_top_waiter(). This means that futex_lock_pi() of said futex_q * has dropped the hb->lock in between queue_me() and unqueue_me_pi(), * which in turn means that futex_lock_pi() still has a reference on * our pi_state. * * The waiter holding a reference on @pi_state also protects against * the unlocked put_pi_state() in futex_unlock_pi(), futex_lock_pi() * and futex_wait_requeue_pi() as it cannot go to 0 and consequently * free pi_state before we can take a reference ourselves. */ WARN_ON(!atomic_read(&pi_state->refcount)); /* * Now that we have a pi_state, we can acquire wait_lock * and do the state validation. */ raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); /* * Since {uval, pi_state} is serialized by wait_lock, and our current * uval was read without holding it, it can have changed. Verify it * still is what we expect it to be, otherwise retry the entire * operation. */ if (get_futex_value_locked(&uval2, uaddr)) goto out_efault; if (uval != uval2) goto out_eagain; /* * Handle the owner died case: */ if (uval & FUTEX_OWNER_DIED) { /* * exit_pi_state_list sets owner to NULL and wakes the * topmost waiter. The task which acquires the * pi_state->rt_mutex will fixup owner. */ if (!pi_state->owner) { /* * No pi state owner, but the user space TID * is not 0. Inconsistent state. [5] */ if (pid) goto out_einval; /* * Take a ref on the state and return success. [4] */ goto out_attach; } /* * If TID is 0, then either the dying owner has not * yet executed exit_pi_state_list() or some waiter * acquired the rtmutex in the pi state, but did not * yet fixup the TID in user space. * * Take a ref on the state and return success. [6] */ if (!pid) goto out_attach; } else { /* * If the owner died bit is not set, then the pi_state * must have an owner. [7] */ if (!pi_state->owner) goto out_einval; } /* * Bail out if user space manipulated the futex value. If pi * state exists then the owner TID must be the same as the * user space TID. [9/10] */ if (pid != task_pid_vnr(pi_state->owner)) goto out_einval; out_attach: get_pi_state(pi_state); raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); *ps = pi_state; return 0; out_einval: ret = -EINVAL; goto out_error; out_eagain: ret = -EAGAIN; goto out_error; out_efault: ret = -EFAULT; goto out_error; out_error: raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); return ret; } static int handle_exit_race(u32 __user *uaddr, u32 uval, struct task_struct *tsk) { u32 uval2; /* * If PF_EXITPIDONE is not yet set, then try again. */ if (tsk && !(tsk->flags & PF_EXITPIDONE)) return -EAGAIN; /* * Reread the user space value to handle the following situation: * * CPU0 CPU1 * * sys_exit() sys_futex() * do_exit() futex_lock_pi() * futex_lock_pi_atomic() * exit_signals(tsk) No waiters: * tsk->flags |= PF_EXITING; *uaddr == 0x00000PID * mm_release(tsk) Set waiter bit * exit_robust_list(tsk) { *uaddr = 0x80000PID; * Set owner died attach_to_pi_owner() { * *uaddr = 0xC0000000; tsk = get_task(PID); * } if (!tsk->flags & PF_EXITING) { * ... attach(); * tsk->flags |= PF_EXITPIDONE; } else { * if (!(tsk->flags & PF_EXITPIDONE)) * return -EAGAIN; * return -ESRCH; <--- FAIL * } * * Returning ESRCH unconditionally is wrong here because the * user space value has been changed by the exiting task. * * The same logic applies to the case where the exiting task is * already gone. */ if (get_futex_value_locked(&uval2, uaddr)) return -EFAULT; /* If the user space value has changed, try again. */ if (uval2 != uval) return -EAGAIN; /* * The exiting task did not have a robust list, the robust list was * corrupted or the user space value in *uaddr is simply bogus. * Give up and tell user space. */ return -ESRCH; } /* * Lookup the task for the TID provided from user space and attach to * it after doing proper sanity checks. */ static int attach_to_pi_owner(u32 __user *uaddr, u32 uval, union futex_key *key, struct futex_pi_state **ps) { pid_t pid = uval & FUTEX_TID_MASK; struct futex_pi_state *pi_state; struct task_struct *p; /* * We are the first waiter - try to look up the real owner and attach * the new pi_state to it, but bail out when TID = 0 [1] * * The !pid check is paranoid. None of the call sites should end up * with pid == 0, but better safe than sorry. Let the caller retry */ if (!pid) return -EAGAIN; p = find_get_task_by_vpid(pid); if (!p) return handle_exit_race(uaddr, uval, NULL); if (unlikely(p->flags & PF_KTHREAD)) { put_task_struct(p); return -EPERM; } /* * We need to look at the task state flags to figure out, * whether the task is exiting. To protect against the do_exit * change of the task flags, we do this protected by * p->pi_lock: */ raw_spin_lock_irq(&p->pi_lock); if (unlikely(p->flags & PF_EXITING)) { /* * The task is on the way out. When PF_EXITPIDONE is * set, we know that the task has finished the * cleanup: */ int ret = handle_exit_race(uaddr, uval, p); raw_spin_unlock_irq(&p->pi_lock); put_task_struct(p); return ret; } /* * No existing pi state. First waiter. [2] * * This creates pi_state, we have hb->lock held, this means nothing can * observe this state, wait_lock is irrelevant. */ pi_state = alloc_pi_state(); /* * Initialize the pi_mutex in locked state and make @p * the owner of it: */ rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p); /* Store the key for possible exit cleanups: */ pi_state->key = *key; WARN_ON(!list_empty(&pi_state->list)); list_add(&pi_state->list, &p->pi_state_list); /* * Assignment without holding pi_state->pi_mutex.wait_lock is safe * because there is no concurrency as the object is not published yet. */ pi_state->owner = p; raw_spin_unlock_irq(&p->pi_lock); put_task_struct(p); *ps = pi_state; return 0; } static int lookup_pi_state(u32 __user *uaddr, u32 uval, struct futex_hash_bucket *hb, union futex_key *key, struct futex_pi_state **ps) { struct futex_q *top_waiter = futex_top_waiter(hb, key); /* * If there is a waiter on that futex, validate it and * attach to the pi_state when the validation succeeds. */ if (top_waiter) return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps); /* * We are the first waiter - try to look up the owner based on * @uval and attach to it. */ return attach_to_pi_owner(uaddr, uval, key, ps); } static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval) { u32 uninitialized_var(curval); if (unlikely(should_fail_futex(true))) return -EFAULT; if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))) return -EFAULT; /* If user space value changed, let the caller retry */ return curval != uval ? -EAGAIN : 0; } /** * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex * @uaddr: the pi futex user address * @hb: the pi futex hash bucket * @key: the futex key associated with uaddr and hb * @ps: the pi_state pointer where we store the result of the * lookup * @task: the task to perform the atomic lock work for. This will * be "current" except in the case of requeue pi. * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0) * * Return: * - 0 - ready to wait; * - 1 - acquired the lock; * - <0 - error * * The hb->lock and futex_key refs shall be held by the caller. */ static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb, union futex_key *key, struct futex_pi_state **ps, struct task_struct *task, int set_waiters) { u32 uval, newval, vpid = task_pid_vnr(task); struct futex_q *top_waiter; int ret; /* * Read the user space value first so we can validate a few * things before proceeding further. */ if (get_futex_value_locked(&uval, uaddr)) return -EFAULT; if (unlikely(should_fail_futex(true))) return -EFAULT; /* * Detect deadlocks. */ if ((unlikely((uval & FUTEX_TID_MASK) == vpid))) return -EDEADLK; if ((unlikely(should_fail_futex(true)))) return -EDEADLK; /* * Lookup existing state first. If it exists, try to attach to * its pi_state. */ top_waiter = futex_top_waiter(hb, key); if (top_waiter) return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps); /* * No waiter and user TID is 0. We are here because the * waiters or the owner died bit is set or called from * requeue_cmp_pi or for whatever reason something took the * syscall. */ if (!(uval & FUTEX_TID_MASK)) { /* * We take over the futex. No other waiters and the user space * TID is 0. We preserve the owner died bit. */ newval = uval & FUTEX_OWNER_DIED; newval |= vpid; /* The futex requeue_pi code can enforce the waiters bit */ if (set_waiters) newval |= FUTEX_WAITERS; ret = lock_pi_update_atomic(uaddr, uval, newval); /* If the take over worked, return 1 */ return ret < 0 ? ret : 1; } /* * First waiter. Set the waiters bit before attaching ourself to * the owner. If owner tries to unlock, it will be forced into * the kernel and blocked on hb->lock. */ newval = uval | FUTEX_WAITERS; ret = lock_pi_update_atomic(uaddr, uval, newval); if (ret) return ret; /* * If the update of the user space value succeeded, we try to * attach to the owner. If that fails, no harm done, we only * set the FUTEX_WAITERS bit in the user space variable. */ return attach_to_pi_owner(uaddr, newval, key, ps); } /** * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket * @q: The futex_q to unqueue * * The q->lock_ptr must not be NULL and must be held by the caller. */ static void __unqueue_futex(struct futex_q *q) { struct futex_hash_bucket *hb; if (WARN_ON_SMP(!q->lock_ptr) || WARN_ON(plist_node_empty(&q->list))) return; lockdep_assert_held(q->lock_ptr); hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock); plist_del(&q->list, &hb->chain); hb_waiters_dec(hb); } /* * The hash bucket lock must be held when this is called. * Afterwards, the futex_q must not be accessed. Callers * must ensure to later call wake_up_q() for the actual * wakeups to occur. */ static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q) { struct task_struct *p = q->task; if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n")) return; get_task_struct(p); __unqueue_futex(q); /* * The waiting task can free the futex_q as soon as q->lock_ptr = NULL * is written, without taking any locks. This is possible in the event * of a spurious wakeup, for example. A memory barrier is required here * to prevent the following store to lock_ptr from getting ahead of the * plist_del in __unqueue_futex(). */ smp_store_release(&q->lock_ptr, NULL); /* * Queue the task for later wakeup for after we've released * the hb->lock. wake_q_add() grabs reference to p. */ wake_q_add(wake_q, p); put_task_struct(p); } /* * Caller must hold a reference on @pi_state. */ static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state) { u32 uninitialized_var(curval), newval; struct task_struct *new_owner; bool postunlock = false; DEFINE_WAKE_Q(wake_q); int ret = 0; new_owner = rt_mutex_next_owner(&pi_state->pi_mutex); if (WARN_ON_ONCE(!new_owner)) { /* * As per the comment in futex_unlock_pi() this should not happen. * * When this happens, give up our locks and try again, giving * the futex_lock_pi() instance time to complete, either by * waiting on the rtmutex or removing itself from the futex * queue. */ ret = -EAGAIN; goto out_unlock; } /* * We pass it to the next owner. The WAITERS bit is always kept * enabled while there is PI state around. We cleanup the owner * died bit, because we are the owner. */ newval = FUTEX_WAITERS | task_pid_vnr(new_owner); if (unlikely(should_fail_futex(true))) ret = -EFAULT; if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)) { ret = -EFAULT; } else if (curval != uval) { /* * If a unconditional UNLOCK_PI operation (user space did not * try the TID->0 transition) raced with a waiter setting the * FUTEX_WAITERS flag between get_user() and locking the hash * bucket lock, retry the operation. */ if ((FUTEX_TID_MASK & curval) == uval) ret = -EAGAIN; else ret = -EINVAL; } if (ret) goto out_unlock; /* * This is a point of no return; once we modify the uval there is no * going back and subsequent operations must not fail. */ raw_spin_lock(&pi_state->owner->pi_lock); WARN_ON(list_empty(&pi_state->list)); list_del_init(&pi_state->list); raw_spin_unlock(&pi_state->owner->pi_lock); raw_spin_lock(&new_owner->pi_lock); WARN_ON(!list_empty(&pi_state->list)); list_add(&pi_state->list, &new_owner->pi_state_list); pi_state->owner = new_owner; raw_spin_unlock(&new_owner->pi_lock); postunlock = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q); out_unlock: raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); if (postunlock) rt_mutex_postunlock(&wake_q); return ret; } /* * Express the locking dependencies for lockdep: */ static inline void double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2) { if (hb1 <= hb2) { spin_lock(&hb1->lock); if (hb1 < hb2) spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING); } else { /* hb1 > hb2 */ spin_lock(&hb2->lock); spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING); } } static inline void double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2) { spin_unlock(&hb1->lock); if (hb1 != hb2) spin_unlock(&hb2->lock); } /* * Wake up waiters matching bitset queued on this futex (uaddr). */ static int futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset) { struct futex_hash_bucket *hb; struct futex_q *this, *next; union futex_key key = FUTEX_KEY_INIT; int ret; DEFINE_WAKE_Q(wake_q); if (!bitset) return -EINVAL; ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_READ); if (unlikely(ret != 0)) goto out; hb = hash_futex(&key); /* Make sure we really have tasks to wakeup */ if (!hb_waiters_pending(hb)) goto out_put_key; spin_lock(&hb->lock); plist_for_each_entry_safe(this, next, &hb->chain, list) { if (match_futex (&this->key, &key)) { if (this->pi_state || this->rt_waiter) { ret = -EINVAL; break; } /* Check if one of the bits is set in both bitsets */ if (!(this->bitset & bitset)) continue; mark_wake_futex(&wake_q, this); if (++ret >= nr_wake) break; } } spin_unlock(&hb->lock); wake_up_q(&wake_q); out_put_key: put_futex_key(&key); out: return ret; } static int futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr) { unsigned int op = (encoded_op & 0x70000000) >> 28; unsigned int cmp = (encoded_op & 0x0f000000) >> 24; int oparg = sign_extend32((encoded_op & 0x00fff000) >> 12, 11); int cmparg = sign_extend32(encoded_op & 0x00000fff, 11); int oldval, ret; if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) { if (oparg < 0 || oparg > 31) { char comm[sizeof(current->comm)]; /* * kill this print and return -EINVAL when userspace * is sane again */ pr_info_ratelimited("futex_wake_op: %s tries to shift op by %d; fix this program\n", get_task_comm(comm, current), oparg); oparg &= 31; } oparg = 1 << oparg; } if (!access_ok(uaddr, sizeof(u32))) return -EFAULT; ret = arch_futex_atomic_op_inuser(op, oparg, &oldval, uaddr); if (ret) return ret; switch (cmp) { case FUTEX_OP_CMP_EQ: return oldval == cmparg; case FUTEX_OP_CMP_NE: return oldval != cmparg; case FUTEX_OP_CMP_LT: return oldval < cmparg; case FUTEX_OP_CMP_GE: return oldval >= cmparg; case FUTEX_OP_CMP_LE: return oldval <= cmparg; case FUTEX_OP_CMP_GT: return oldval > cmparg; default: return -ENOSYS; } } /* * Wake up all waiters hashed on the physical page that is mapped * to this virtual address: */ static int futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2, int nr_wake, int nr_wake2, int op) { union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT; struct futex_hash_bucket *hb1, *hb2; struct futex_q *this, *next; int ret, op_ret; DEFINE_WAKE_Q(wake_q); retry: ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ); if (unlikely(ret != 0)) goto out; ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE); if (unlikely(ret != 0)) goto out_put_key1; hb1 = hash_futex(&key1); hb2 = hash_futex(&key2); retry_private: double_lock_hb(hb1, hb2); op_ret = futex_atomic_op_inuser(op, uaddr2); if (unlikely(op_ret < 0)) { double_unlock_hb(hb1, hb2); #ifndef CONFIG_MMU /* * we don't get EFAULT from MMU faults if we don't have an MMU, * but we might get them from range checking */ ret = op_ret; goto out_put_keys; #endif if (unlikely(op_ret != -EFAULT)) { ret = op_ret; goto out_put_keys; } ret = fault_in_user_writeable(uaddr2); if (ret) goto out_put_keys; if (!(flags & FLAGS_SHARED)) goto retry_private; put_futex_key(&key2); put_futex_key(&key1); goto retry; } plist_for_each_entry_safe(this, next, &hb1->chain, list) { if (match_futex (&this->key, &key1)) { if (this->pi_state || this->rt_waiter) { ret = -EINVAL; goto out_unlock; } mark_wake_futex(&wake_q, this); if (++ret >= nr_wake) break; } } if (op_ret > 0) { op_ret = 0; plist_for_each_entry_safe(this, next, &hb2->chain, list) { if (match_futex (&this->key, &key2)) { if (this->pi_state || this->rt_waiter) { ret = -EINVAL; goto out_unlock; } mark_wake_futex(&wake_q, this); if (++op_ret >= nr_wake2) break; } } ret += op_ret; } out_unlock: double_unlock_hb(hb1, hb2); wake_up_q(&wake_q); out_put_keys: put_futex_key(&key2); out_put_key1: put_futex_key(&key1); out: return ret; } /** * requeue_futex() - Requeue a futex_q from one hb to another * @q: the futex_q to requeue * @hb1: the source hash_bucket * @hb2: the target hash_bucket * @key2: the new key for the requeued futex_q */ static inline void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2, union futex_key *key2) { /* * If key1 and key2 hash to the same bucket, no need to * requeue. */ if (likely(&hb1->chain != &hb2->chain)) { plist_del(&q->list, &hb1->chain); hb_waiters_dec(hb1); hb_waiters_inc(hb2); plist_add(&q->list, &hb2->chain); q->lock_ptr = &hb2->lock; } get_futex_key_refs(key2); q->key = *key2; } /** * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue * @q: the futex_q * @key: the key of the requeue target futex * @hb: the hash_bucket of the requeue target futex * * During futex_requeue, with requeue_pi=1, it is possible to acquire the * target futex if it is uncontended or via a lock steal. Set the futex_q key * to the requeue target futex so the waiter can detect the wakeup on the right * futex, but remove it from the hb and NULL the rt_waiter so it can detect * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock * to protect access to the pi_state to fixup the owner later. Must be called * with both q->lock_ptr and hb->lock held. */ static inline void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key, struct futex_hash_bucket *hb) { get_futex_key_refs(key); q->key = *key; __unqueue_futex(q); WARN_ON(!q->rt_waiter); q->rt_waiter = NULL; q->lock_ptr = &hb->lock; wake_up_state(q->task, TASK_NORMAL); } /** * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter * @pifutex: the user address of the to futex * @hb1: the from futex hash bucket, must be locked by the caller * @hb2: the to futex hash bucket, must be locked by the caller * @key1: the from futex key * @key2: the to futex key * @ps: address to store the pi_state pointer * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0) * * Try and get the lock on behalf of the top waiter if we can do it atomically. * Wake the top waiter if we succeed. If the caller specified set_waiters, * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit. * hb1 and hb2 must be held by the caller. * * Return: * - 0 - failed to acquire the lock atomically; * - >0 - acquired the lock, return value is vpid of the top_waiter * - <0 - error */ static int futex_proxy_trylock_atomic(u32 __user *pifutex, struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2, union futex_key *key1, union futex_key *key2, struct futex_pi_state **ps, int set_waiters) { struct futex_q *top_waiter = NULL; u32 curval; int ret, vpid; if (get_futex_value_locked(&curval, pifutex)) return -EFAULT; if (unlikely(should_fail_futex(true))) return -EFAULT; /* * Find the top_waiter and determine if there are additional waiters. * If the caller intends to requeue more than 1 waiter to pifutex, * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now, * as we have means to handle the possible fault. If not, don't set * the bit unecessarily as it will force the subsequent unlock to enter * the kernel. */ top_waiter = futex_top_waiter(hb1, key1); /* There are no waiters, nothing for us to do. */ if (!top_waiter) return 0; /* Ensure we requeue to the expected futex. */ if (!match_futex(top_waiter->requeue_pi_key, key2)) return -EINVAL; /* * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in * the contended case or if set_waiters is 1. The pi_state is returned * in ps in contended cases. */ vpid = task_pid_vnr(top_waiter->task); ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task, set_waiters); if (ret == 1) { requeue_pi_wake_futex(top_waiter, key2, hb2); return vpid; } return ret; } /** * futex_requeue() - Requeue waiters from uaddr1 to uaddr2 * @uaddr1: source futex user address * @flags: futex flags (FLAGS_SHARED, etc.) * @uaddr2: target futex user address * @nr_wake: number of waiters to wake (must be 1 for requeue_pi) * @nr_requeue: number of waiters to requeue (0-INT_MAX) * @cmpval: @uaddr1 expected value (or %NULL) * @requeue_pi: if we are attempting to requeue from a non-pi futex to a * pi futex (pi to pi requeue is not supported) * * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire * uaddr2 atomically on behalf of the top waiter. * * Return: * - >=0 - on success, the number of tasks requeued or woken; * - <0 - on error */ static int futex_requeue(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2, int nr_wake, int nr_requeue, u32 *cmpval, int requeue_pi) { union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT; int drop_count = 0, task_count = 0, ret; struct futex_pi_state *pi_state = NULL; struct futex_hash_bucket *hb1, *hb2; struct futex_q *this, *next; DEFINE_WAKE_Q(wake_q); if (nr_wake < 0 || nr_requeue < 0) return -EINVAL; /* * When PI not supported: return -ENOSYS if requeue_pi is true, * consequently the compiler knows requeue_pi is always false past * this point which will optimize away all the conditional code * further down. */ if (!IS_ENABLED(CONFIG_FUTEX_PI) && requeue_pi) return -ENOSYS; if (requeue_pi) { /* * Requeue PI only works on two distinct uaddrs. This * check is only valid for private futexes. See below. */ if (uaddr1 == uaddr2) return -EINVAL; /* * requeue_pi requires a pi_state, try to allocate it now * without any locks in case it fails. */ if (refill_pi_state_cache()) return -ENOMEM; /* * requeue_pi must wake as many tasks as it can, up to nr_wake * + nr_requeue, since it acquires the rt_mutex prior to * returning to userspace, so as to not leave the rt_mutex with * waiters and no owner. However, second and third wake-ups * cannot be predicted as they involve race conditions with the * first wake and a fault while looking up the pi_state. Both * pthread_cond_signal() and pthread_cond_broadcast() should * use nr_wake=1. */ if (nr_wake != 1) return -EINVAL; } retry: ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ); if (unlikely(ret != 0)) goto out; ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, requeue_pi ? FUTEX_WRITE : FUTEX_READ); if (unlikely(ret != 0)) goto out_put_key1; /* * The check above which compares uaddrs is not sufficient for * shared futexes. We need to compare the keys: */ if (requeue_pi && match_futex(&key1, &key2)) { ret = -EINVAL; goto out_put_keys; } hb1 = hash_futex(&key1); hb2 = hash_futex(&key2); retry_private: hb_waiters_inc(hb2); double_lock_hb(hb1, hb2); if (likely(cmpval != NULL)) { u32 curval; ret = get_futex_value_locked(&curval, uaddr1); if (unlikely(ret)) { double_unlock_hb(hb1, hb2); hb_waiters_dec(hb2); ret = get_user(curval, uaddr1); if (ret) goto out_put_keys; if (!(flags & FLAGS_SHARED)) goto retry_private; put_futex_key(&key2); put_futex_key(&key1); goto retry; } if (curval != *cmpval) { ret = -EAGAIN; goto out_unlock; } } if (requeue_pi && (task_count - nr_wake < nr_requeue)) { /* * Attempt to acquire uaddr2 and wake the top waiter. If we * intend to requeue waiters, force setting the FUTEX_WAITERS * bit. We force this here where we are able to easily handle * faults rather in the requeue loop below. */ ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1, &key2, &pi_state, nr_requeue); /* * At this point the top_waiter has either taken uaddr2 or is * waiting on it. If the former, then the pi_state will not * exist yet, look it up one more time to ensure we have a * reference to it. If the lock was taken, ret contains the * vpid of the top waiter task. * If the lock was not taken, we have pi_state and an initial * refcount on it. In case of an error we have nothing. */ if (ret > 0) { WARN_ON(pi_state); drop_count++; task_count++; /* * If we acquired the lock, then the user space value * of uaddr2 should be vpid. It cannot be changed by * the top waiter as it is blocked on hb2 lock if it * tries to do so. If something fiddled with it behind * our back the pi state lookup might unearth it. So * we rather use the known value than rereading and * handing potential crap to lookup_pi_state. * * If that call succeeds then we have pi_state and an * initial refcount on it. */ ret = lookup_pi_state(uaddr2, ret, hb2, &key2, &pi_state); } switch (ret) { case 0: /* We hold a reference on the pi state. */ break; /* If the above failed, then pi_state is NULL */ case -EFAULT: double_unlock_hb(hb1, hb2); hb_waiters_dec(hb2); put_futex_key(&key2); put_futex_key(&key1); ret = fault_in_user_writeable(uaddr2); if (!ret) goto retry; goto out; case -EAGAIN: /* * Two reasons for this: * - Owner is exiting and we just wait for the * exit to complete. * - The user space value changed. */ double_unlock_hb(hb1, hb2); hb_waiters_dec(hb2); put_futex_key(&key2); put_futex_key(&key1); cond_resched(); goto retry; default: goto out_unlock; } } plist_for_each_entry_safe(this, next, &hb1->chain, list) { if (task_count - nr_wake >= nr_requeue) break; if (!match_futex(&this->key, &key1)) continue; /* * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always * be paired with each other and no other futex ops. * * We should never be requeueing a futex_q with a pi_state, * which is awaiting a futex_unlock_pi(). */ if ((requeue_pi && !this->rt_waiter) || (!requeue_pi && this->rt_waiter) || this->pi_state) { ret = -EINVAL; break; } /* * Wake nr_wake waiters. For requeue_pi, if we acquired the * lock, we already woke the top_waiter. If not, it will be * woken by futex_unlock_pi(). */ if (++task_count <= nr_wake && !requeue_pi) { mark_wake_futex(&wake_q, this); continue; } /* Ensure we requeue to the expected futex for requeue_pi. */ if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) { ret = -EINVAL; break; } /* * Requeue nr_requeue waiters and possibly one more in the case * of requeue_pi if we couldn't acquire the lock atomically. */ if (requeue_pi) { /* * Prepare the waiter to take the rt_mutex. Take a * refcount on the pi_state and store the pointer in * the futex_q object of the waiter. */ get_pi_state(pi_state); this->pi_state = pi_state; ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex, this->rt_waiter, this->task); if (ret == 1) { /* * We got the lock. We do neither drop the * refcount on pi_state nor clear * this->pi_state because the waiter needs the * pi_state for cleaning up the user space * value. It will drop the refcount after * doing so. */ requeue_pi_wake_futex(this, &key2, hb2); drop_count++; continue; } else if (ret) { /* * rt_mutex_start_proxy_lock() detected a * potential deadlock when we tried to queue * that waiter. Drop the pi_state reference * which we took above and remove the pointer * to the state from the waiters futex_q * object. */ this->pi_state = NULL; put_pi_state(pi_state); /* * We stop queueing more waiters and let user * space deal with the mess. */ break; } } requeue_futex(this, hb1, hb2, &key2); drop_count++; } /* * We took an extra initial reference to the pi_state either * in futex_proxy_trylock_atomic() or in lookup_pi_state(). We * need to drop it here again. */ put_pi_state(pi_state); out_unlock: double_unlock_hb(hb1, hb2); wake_up_q(&wake_q); hb_waiters_dec(hb2); /* * drop_futex_key_refs() must be called outside the spinlocks. During * the requeue we moved futex_q's from the hash bucket at key1 to the * one at key2 and updated their key pointer. We no longer need to * hold the references to key1. */ while (--drop_count >= 0) drop_futex_key_refs(&key1); out_put_keys: put_futex_key(&key2); out_put_key1: put_futex_key(&key1); out: return ret ? ret : task_count; } /* The key must be already stored in q->key. */ static inline struct futex_hash_bucket *queue_lock(struct futex_q *q) __acquires(&hb->lock) { struct futex_hash_bucket *hb; hb = hash_futex(&q->key); /* * Increment the counter before taking the lock so that * a potential waker won't miss a to-be-slept task that is * waiting for the spinlock. This is safe as all queue_lock() * users end up calling queue_me(). Similarly, for housekeeping, * decrement the counter at queue_unlock() when some error has * occurred and we don't end up adding the task to the list. */ hb_waiters_inc(hb); /* implies smp_mb(); (A) */ q->lock_ptr = &hb->lock; spin_lock(&hb->lock); return hb; } static inline void queue_unlock(struct futex_hash_bucket *hb) __releases(&hb->lock) { spin_unlock(&hb->lock); hb_waiters_dec(hb); } static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb) { int prio; /* * The priority used to register this element is * - either the real thread-priority for the real-time threads * (i.e. threads with a priority lower than MAX_RT_PRIO) * - or MAX_RT_PRIO for non-RT threads. * Thus, all RT-threads are woken first in priority order, and * the others are woken last, in FIFO order. */ prio = min(current->normal_prio, MAX_RT_PRIO); plist_node_init(&q->list, prio); plist_add(&q->list, &hb->chain); q->task = current; } /** * queue_me() - Enqueue the futex_q on the futex_hash_bucket * @q: The futex_q to enqueue * @hb: The destination hash bucket * * The hb->lock must be held by the caller, and is released here. A call to * queue_me() is typically paired with exactly one call to unqueue_me(). The * exceptions involve the PI related operations, which may use unqueue_me_pi() * or nothing if the unqueue is done as part of the wake process and the unqueue * state is implicit in the state of woken task (see futex_wait_requeue_pi() for * an example). */ static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb) __releases(&hb->lock) { __queue_me(q, hb); spin_unlock(&hb->lock); } /** * unqueue_me() - Remove the futex_q from its futex_hash_bucket * @q: The futex_q to unqueue * * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must * be paired with exactly one earlier call to queue_me(). * * Return: * - 1 - if the futex_q was still queued (and we removed unqueued it); * - 0 - if the futex_q was already removed by the waking thread */ static int unqueue_me(struct futex_q *q) { spinlock_t *lock_ptr; int ret = 0; /* In the common case we don't take the spinlock, which is nice. */ retry: /* * q->lock_ptr can change between this read and the following spin_lock. * Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and * optimizing lock_ptr out of the logic below. */ lock_ptr = READ_ONCE(q->lock_ptr); if (lock_ptr != NULL) { spin_lock(lock_ptr); /* * q->lock_ptr can change between reading it and * spin_lock(), causing us to take the wrong lock. This * corrects the race condition. * * Reasoning goes like this: if we have the wrong lock, * q->lock_ptr must have changed (maybe several times) * between reading it and the spin_lock(). It can * change again after the spin_lock() but only if it was * already changed before the spin_lock(). It cannot, * however, change back to the original value. Therefore * we can detect whether we acquired the correct lock. */ if (unlikely(lock_ptr != q->lock_ptr)) { spin_unlock(lock_ptr); goto retry; } __unqueue_futex(q); BUG_ON(q->pi_state); spin_unlock(lock_ptr); ret = 1; } drop_futex_key_refs(&q->key); return ret; } /* * PI futexes can not be requeued and must remove themself from the * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry * and dropped here. */ static void unqueue_me_pi(struct futex_q *q) __releases(q->lock_ptr) { __unqueue_futex(q); BUG_ON(!q->pi_state); put_pi_state(q->pi_state); q->pi_state = NULL; spin_unlock(q->lock_ptr); } static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q, struct task_struct *argowner) { struct futex_pi_state *pi_state = q->pi_state; u32 uval, uninitialized_var(curval), newval; struct task_struct *oldowner, *newowner; u32 newtid; int ret; lockdep_assert_held(q->lock_ptr); raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); oldowner = pi_state->owner; /* * We are here because either: * * - we stole the lock and pi_state->owner needs updating to reflect * that (@argowner == current), * * or: * * - someone stole our lock and we need to fix things to point to the * new owner (@argowner == NULL). * * Either way, we have to replace the TID in the user space variable. * This must be atomic as we have to preserve the owner died bit here. * * Note: We write the user space value _before_ changing the pi_state * because we can fault here. Imagine swapped out pages or a fork * that marked all the anonymous memory readonly for cow. * * Modifying pi_state _before_ the user space value would leave the * pi_state in an inconsistent state when we fault here, because we * need to drop the locks to handle the fault. This might be observed * in the PID check in lookup_pi_state. */ retry: if (!argowner) { if (oldowner != current) { /* * We raced against a concurrent self; things are * already fixed up. Nothing to do. */ ret = 0; goto out_unlock; } if (__rt_mutex_futex_trylock(&pi_state->pi_mutex)) { /* We got the lock after all, nothing to fix. */ ret = 0; goto out_unlock; } /* * Since we just failed the trylock; there must be an owner. */ newowner = rt_mutex_owner(&pi_state->pi_mutex); BUG_ON(!newowner); } else { WARN_ON_ONCE(argowner != current); if (oldowner == current) { /* * We raced against a concurrent self; things are * already fixed up. Nothing to do. */ ret = 0; goto out_unlock; } newowner = argowner; } newtid = task_pid_vnr(newowner) | FUTEX_WAITERS; /* Owner died? */ if (!pi_state->owner) newtid |= FUTEX_OWNER_DIED; if (get_futex_value_locked(&uval, uaddr)) goto handle_fault; for (;;) { newval = (uval & FUTEX_OWNER_DIED) | newtid; if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)) goto handle_fault; if (curval == uval) break; uval = curval; } /* * We fixed up user space. Now we need to fix the pi_state * itself. */ if (pi_state->owner != NULL) { raw_spin_lock(&pi_state->owner->pi_lock); WARN_ON(list_empty(&pi_state->list)); list_del_init(&pi_state->list); raw_spin_unlock(&pi_state->owner->pi_lock); } pi_state->owner = newowner; raw_spin_lock(&newowner->pi_lock); WARN_ON(!list_empty(&pi_state->list)); list_add(&pi_state->list, &newowner->pi_state_list); raw_spin_unlock(&newowner->pi_lock); raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); return 0; /* * To handle the page fault we need to drop the locks here. That gives * the other task (either the highest priority waiter itself or the * task which stole the rtmutex) the chance to try the fixup of the * pi_state. So once we are back from handling the fault we need to * check the pi_state after reacquiring the locks and before trying to * do another fixup. When the fixup has been done already we simply * return. * * Note: we hold both hb->lock and pi_mutex->wait_lock. We can safely * drop hb->lock since the caller owns the hb -> futex_q relation. * Dropping the pi_mutex->wait_lock requires the state revalidate. */ handle_fault: raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); spin_unlock(q->lock_ptr); ret = fault_in_user_writeable(uaddr); spin_lock(q->lock_ptr); raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); /* * Check if someone else fixed it for us: */ if (pi_state->owner != oldowner) { ret = 0; goto out_unlock; } if (ret) goto out_unlock; goto retry; out_unlock: raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); return ret; } static long futex_wait_restart(struct restart_block *restart); /** * fixup_owner() - Post lock pi_state and corner case management * @uaddr: user address of the futex * @q: futex_q (contains pi_state and access to the rt_mutex) * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0) * * After attempting to lock an rt_mutex, this function is called to cleanup * the pi_state owner as well as handle race conditions that may allow us to * acquire the lock. Must be called with the hb lock held. * * Return: * - 1 - success, lock taken; * - 0 - success, lock not taken; * - <0 - on error (-EFAULT) */ static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked) { int ret = 0; if (locked) { /* * Got the lock. We might not be the anticipated owner if we * did a lock-steal - fix up the PI-state in that case: * * Speculative pi_state->owner read (we don't hold wait_lock); * since we own the lock pi_state->owner == current is the * stable state, anything else needs more attention. */ if (q->pi_state->owner != current) ret = fixup_pi_state_owner(uaddr, q, current); goto out; } /* * If we didn't get the lock; check if anybody stole it from us. In * that case, we need to fix up the uval to point to them instead of * us, otherwise bad things happen. [10] * * Another speculative read; pi_state->owner == current is unstable * but needs our attention. */ if (q->pi_state->owner == current) { ret = fixup_pi_state_owner(uaddr, q, NULL); goto out; } /* * Paranoia check. If we did not take the lock, then we should not be * the owner of the rt_mutex. */ if (rt_mutex_owner(&q->pi_state->pi_mutex) == current) { printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p " "pi-state %p\n", ret, q->pi_state->pi_mutex.owner, q->pi_state->owner); } out: return ret ? ret : locked; } /** * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal * @hb: the futex hash bucket, must be locked by the caller * @q: the futex_q to queue up on * @timeout: the prepared hrtimer_sleeper, or null for no timeout */ static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q, struct hrtimer_sleeper *timeout) { /* * The task state is guaranteed to be set before another task can * wake it. set_current_state() is implemented using smp_store_mb() and * queue_me() calls spin_unlock() upon completion, both serializing * access to the hash list and forcing another memory barrier. */ set_current_state(TASK_INTERRUPTIBLE); queue_me(q, hb); /* Arm the timer */ if (timeout) hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS); /* * If we have been removed from the hash list, then another task * has tried to wake us, and we can skip the call to schedule(). */ if (likely(!plist_node_empty(&q->list))) { /* * If the timer has already expired, current will already be * flagged for rescheduling. Only call schedule if there * is no timeout, or if it has yet to expire. */ if (!timeout || timeout->task) freezable_schedule(); } __set_current_state(TASK_RUNNING); } /** * futex_wait_setup() - Prepare to wait on a futex * @uaddr: the futex userspace address * @val: the expected value * @flags: futex flags (FLAGS_SHARED, etc.) * @q: the associated futex_q * @hb: storage for hash_bucket pointer to be returned to caller * * Setup the futex_q and locate the hash_bucket. Get the futex value and * compare it with the expected value. Handle atomic faults internally. * Return with the hb lock held and a q.key reference on success, and unlocked * with no q.key reference on failure. * * Return: * - 0 - uaddr contains val and hb has been locked; * - <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked */ static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags, struct futex_q *q, struct futex_hash_bucket **hb) { u32 uval; int ret; /* * Access the page AFTER the hash-bucket is locked. * Order is important: * * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val); * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); } * * The basic logical guarantee of a futex is that it blocks ONLY * if cond(var) is known to be true at the time of blocking, for * any cond. If we locked the hash-bucket after testing *uaddr, that * would open a race condition where we could block indefinitely with * cond(var) false, which would violate the guarantee. * * On the other hand, we insert q and release the hash-bucket only * after testing *uaddr. This guarantees that futex_wait() will NOT * absorb a wakeup if *uaddr does not match the desired values * while the syscall executes. */ retry: ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, FUTEX_READ); if (unlikely(ret != 0)) return ret; retry_private: *hb = queue_lock(q); ret = get_futex_value_locked(&uval, uaddr); if (ret) { queue_unlock(*hb); ret = get_user(uval, uaddr); if (ret) goto out; if (!(flags & FLAGS_SHARED)) goto retry_private; put_futex_key(&q->key); goto retry; } if (uval != val) { queue_unlock(*hb); ret = -EWOULDBLOCK; } out: if (ret) put_futex_key(&q->key); return ret; } static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val, ktime_t *abs_time, u32 bitset) { struct hrtimer_sleeper timeout, *to = NULL; struct restart_block *restart; struct futex_hash_bucket *hb; struct futex_q q = futex_q_init; int ret; if (!bitset) return -EINVAL; q.bitset = bitset; if (abs_time) { to = &timeout; hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ? CLOCK_REALTIME : CLOCK_MONOTONIC, HRTIMER_MODE_ABS); hrtimer_init_sleeper(to, current); hrtimer_set_expires_range_ns(&to->timer, *abs_time, current->timer_slack_ns); } retry: /* * Prepare to wait on uaddr. On success, holds hb lock and increments * q.key refs. */ ret = futex_wait_setup(uaddr, val, flags, &q, &hb); if (ret) goto out; /* queue_me and wait for wakeup, timeout, or a signal. */ futex_wait_queue_me(hb, &q, to); /* If we were woken (and unqueued), we succeeded, whatever. */ ret = 0; /* unqueue_me() drops q.key ref */ if (!unqueue_me(&q)) goto out; ret = -ETIMEDOUT; if (to && !to->task) goto out; /* * We expect signal_pending(current), but we might be the * victim of a spurious wakeup as well. */ if (!signal_pending(current)) goto retry; ret = -ERESTARTSYS; if (!abs_time) goto out; restart = ¤t->restart_block; restart->fn = futex_wait_restart; restart->futex.uaddr = uaddr; restart->futex.val = val; restart->futex.time = *abs_time; restart->futex.bitset = bitset; restart->futex.flags = flags | FLAGS_HAS_TIMEOUT; ret = -ERESTART_RESTARTBLOCK; out: if (to) { hrtimer_cancel(&to->timer); destroy_hrtimer_on_stack(&to->timer); } return ret; } static long futex_wait_restart(struct restart_block *restart) { u32 __user *uaddr = restart->futex.uaddr; ktime_t t, *tp = NULL; if (restart->futex.flags & FLAGS_HAS_TIMEOUT) { t = restart->futex.time; tp = &t; } restart->fn = do_no_restart_syscall; return (long)futex_wait(uaddr, restart->futex.flags, restart->futex.val, tp, restart->futex.bitset); } /* * Userspace tried a 0 -> TID atomic transition of the futex value * and failed. The kernel side here does the whole locking operation: * if there are waiters then it will block as a consequence of relying * on rt-mutexes, it does PI, etc. (Due to races the kernel might see * a 0 value of the futex too.). * * Also serves as futex trylock_pi()'ing, and due semantics. */ static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, ktime_t *time, int trylock) { struct hrtimer_sleeper timeout, *to = NULL; struct futex_pi_state *pi_state = NULL; struct rt_mutex_waiter rt_waiter; struct futex_hash_bucket *hb; struct futex_q q = futex_q_init; int res, ret; if (!IS_ENABLED(CONFIG_FUTEX_PI)) return -ENOSYS; if (refill_pi_state_cache()) return -ENOMEM; if (time) { to = &timeout; hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME, HRTIMER_MODE_ABS); hrtimer_init_sleeper(to, current); hrtimer_set_expires(&to->timer, *time); } retry: ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, FUTEX_WRITE); if (unlikely(ret != 0)) goto out; retry_private: hb = queue_lock(&q); ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0); if (unlikely(ret)) { /* * Atomic work succeeded and we got the lock, * or failed. Either way, we do _not_ block. */ switch (ret) { case 1: /* We got the lock. */ ret = 0; goto out_unlock_put_key; case -EFAULT: goto uaddr_faulted; case -EAGAIN: /* * Two reasons for this: * - Task is exiting and we just wait for the * exit to complete. * - The user space value changed. */ queue_unlock(hb); put_futex_key(&q.key); cond_resched(); goto retry; default: goto out_unlock_put_key; } } WARN_ON(!q.pi_state); /* * Only actually queue now that the atomic ops are done: */ __queue_me(&q, hb); if (trylock) { ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex); /* Fixup the trylock return value: */ ret = ret ? 0 : -EWOULDBLOCK; goto no_block; } rt_mutex_init_waiter(&rt_waiter); /* * On PREEMPT_RT_FULL, when hb->lock becomes an rt_mutex, we must not * hold it while doing rt_mutex_start_proxy(), because then it will * include hb->lock in the blocking chain, even through we'll not in * fact hold it while blocking. This will lead it to report -EDEADLK * and BUG when futex_unlock_pi() interleaves with this. * * Therefore acquire wait_lock while holding hb->lock, but drop the * latter before calling __rt_mutex_start_proxy_lock(). This * interleaves with futex_unlock_pi() -- which does a similar lock * handoff -- such that the latter can observe the futex_q::pi_state * before __rt_mutex_start_proxy_lock() is done. */ raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock); spin_unlock(q.lock_ptr); /* * __rt_mutex_start_proxy_lock() unconditionally enqueues the @rt_waiter * such that futex_unlock_pi() is guaranteed to observe the waiter when * it sees the futex_q::pi_state. */ ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current); raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock); if (ret) { if (ret == 1) ret = 0; goto cleanup; } if (unlikely(to)) hrtimer_start_expires(&to->timer, HRTIMER_MODE_ABS); ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter); cleanup: spin_lock(q.lock_ptr); /* * If we failed to acquire the lock (deadlock/signal/timeout), we must * first acquire the hb->lock before removing the lock from the * rt_mutex waitqueue, such that we can keep the hb and rt_mutex wait * lists consistent. * * In particular; it is important that futex_unlock_pi() can not * observe this inconsistency. */ if (ret && !rt_mutex_cleanup_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter)) ret = 0; no_block: /* * Fixup the pi_state owner and possibly acquire the lock if we * haven't already. */ res = fixup_owner(uaddr, &q, !ret); /* * If fixup_owner() returned an error, proprogate that. If it acquired * the lock, clear our -ETIMEDOUT or -EINTR. */ if (res) ret = (res < 0) ? res : 0; /* * If fixup_owner() faulted and was unable to handle the fault, unlock * it and return the fault to userspace. */ if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current)) { pi_state = q.pi_state; get_pi_state(pi_state); } /* Unqueue and drop the lock */ unqueue_me_pi(&q); if (pi_state) { rt_mutex_futex_unlock(&pi_state->pi_mutex); put_pi_state(pi_state); } goto out_put_key; out_unlock_put_key: queue_unlock(hb); out_put_key: put_futex_key(&q.key); out: if (to) { hrtimer_cancel(&to->timer); destroy_hrtimer_on_stack(&to->timer); } return ret != -EINTR ? ret : -ERESTARTNOINTR; uaddr_faulted: queue_unlock(hb); ret = fault_in_user_writeable(uaddr); if (ret) goto out_put_key; if (!(flags & FLAGS_SHARED)) goto retry_private; put_futex_key(&q.key); goto retry; } /* * Userspace attempted a TID -> 0 atomic transition, and failed. * This is the in-kernel slowpath: we look up the PI state (if any), * and do the rt-mutex unlock. */ static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags) { u32 uninitialized_var(curval), uval, vpid = task_pid_vnr(current); union futex_key key = FUTEX_KEY_INIT; struct futex_hash_bucket *hb; struct futex_q *top_waiter; int ret; if (!IS_ENABLED(CONFIG_FUTEX_PI)) return -ENOSYS; retry: if (get_user(uval, uaddr)) return -EFAULT; /* * We release only a lock we actually own: */ if ((uval & FUTEX_TID_MASK) != vpid) return -EPERM; ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_WRITE); if (ret) return ret; hb = hash_futex(&key); spin_lock(&hb->lock); /* * Check waiters first. We do not trust user space values at * all and we at least want to know if user space fiddled * with the futex value instead of blindly unlocking. */ top_waiter = futex_top_waiter(hb, &key); if (top_waiter) { struct futex_pi_state *pi_state = top_waiter->pi_state; ret = -EINVAL; if (!pi_state) goto out_unlock; /* * If current does not own the pi_state then the futex is * inconsistent and user space fiddled with the futex value. */ if (pi_state->owner != current) goto out_unlock; get_pi_state(pi_state); /* * By taking wait_lock while still holding hb->lock, we ensure * there is no point where we hold neither; and therefore * wake_futex_pi() must observe a state consistent with what we * observed. * * In particular; this forces __rt_mutex_start_proxy() to * complete such that we're guaranteed to observe the * rt_waiter. Also see the WARN in wake_futex_pi(). */ raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); spin_unlock(&hb->lock); /* drops pi_state->pi_mutex.wait_lock */ ret = wake_futex_pi(uaddr, uval, pi_state); put_pi_state(pi_state); /* * Success, we're done! No tricky corner cases. */ if (!ret) goto out_putkey; /* * The atomic access to the futex value generated a * pagefault, so retry the user-access and the wakeup: */ if (ret == -EFAULT) goto pi_faulted; /* * A unconditional UNLOCK_PI op raced against a waiter * setting the FUTEX_WAITERS bit. Try again. */ if (ret == -EAGAIN) { put_futex_key(&key); goto retry; } /* * wake_futex_pi has detected invalid state. Tell user * space. */ goto out_putkey; } /* * We have no kernel internal state, i.e. no waiters in the * kernel. Waiters which are about to queue themselves are stuck * on hb->lock. So we can safely ignore them. We do neither * preserve the WAITERS bit not the OWNER_DIED one. We are the * owner. */ if (cmpxchg_futex_value_locked(&curval, uaddr, uval, 0)) { spin_unlock(&hb->lock); goto pi_faulted; } /* * If uval has changed, let user space handle it. */ ret = (curval == uval) ? 0 : -EAGAIN; out_unlock: spin_unlock(&hb->lock); out_putkey: put_futex_key(&key); return ret; pi_faulted: put_futex_key(&key); ret = fault_in_user_writeable(uaddr); if (!ret) goto retry; return ret; } /** * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex * @hb: the hash_bucket futex_q was original enqueued on * @q: the futex_q woken while waiting to be requeued * @key2: the futex_key of the requeue target futex * @timeout: the timeout associated with the wait (NULL if none) * * Detect if the task was woken on the initial futex as opposed to the requeue * target futex. If so, determine if it was a timeout or a signal that caused * the wakeup and return the appropriate error code to the caller. Must be * called with the hb lock held. * * Return: * - 0 = no early wakeup detected; * - <0 = -ETIMEDOUT or -ERESTARTNOINTR */ static inline int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb, struct futex_q *q, union futex_key *key2, struct hrtimer_sleeper *timeout) { int ret = 0; /* * With the hb lock held, we avoid races while we process the wakeup. * We only need to hold hb (and not hb2) to ensure atomicity as the * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb. * It can't be requeued from uaddr2 to something else since we don't * support a PI aware source futex for requeue. */ if (!match_futex(&q->key, key2)) { WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr)); /* * We were woken prior to requeue by a timeout or a signal. * Unqueue the futex_q and determine which it was. */ plist_del(&q->list, &hb->chain); hb_waiters_dec(hb); /* Handle spurious wakeups gracefully */ ret = -EWOULDBLOCK; if (timeout && !timeout->task) ret = -ETIMEDOUT; else if (signal_pending(current)) ret = -ERESTARTNOINTR; } return ret; } /** * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2 * @uaddr: the futex we initially wait on (non-pi) * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be * the same type, no requeueing from private to shared, etc. * @val: the expected value of uaddr * @abs_time: absolute timeout * @bitset: 32 bit wakeup bitset set by userspace, defaults to all * @uaddr2: the pi futex we will take prior to returning to user-space * * The caller will wait on uaddr and will be requeued by futex_requeue() to * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to * userspace. This ensures the rt_mutex maintains an owner when it has waiters; * without one, the pi logic would not know which task to boost/deboost, if * there was a need to. * * We call schedule in futex_wait_queue_me() when we enqueue and return there * via the following-- * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue() * 2) wakeup on uaddr2 after a requeue * 3) signal * 4) timeout * * If 3, cleanup and return -ERESTARTNOINTR. * * If 2, we may then block on trying to take the rt_mutex and return via: * 5) successful lock * 6) signal * 7) timeout * 8) other lock acquisition failure * * If 6, return -EWOULDBLOCK (restarting the syscall would do the same). * * If 4 or 7, we cleanup and return with -ETIMEDOUT. * * Return: * - 0 - On success; * - <0 - On error */ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, u32 val, ktime_t *abs_time, u32 bitset, u32 __user *uaddr2) { struct hrtimer_sleeper timeout, *to = NULL; struct futex_pi_state *pi_state = NULL; struct rt_mutex_waiter rt_waiter; struct futex_hash_bucket *hb; union futex_key key2 = FUTEX_KEY_INIT; struct futex_q q = futex_q_init; int res, ret; if (!IS_ENABLED(CONFIG_FUTEX_PI)) return -ENOSYS; if (uaddr == uaddr2) return -EINVAL; if (!bitset) return -EINVAL; if (abs_time) { to = &timeout; hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ? CLOCK_REALTIME : CLOCK_MONOTONIC, HRTIMER_MODE_ABS); hrtimer_init_sleeper(to, current); hrtimer_set_expires_range_ns(&to->timer, *abs_time, current->timer_slack_ns); } /* * The waiter is allocated on our stack, manipulated by the requeue * code while we sleep on uaddr. */ rt_mutex_init_waiter(&rt_waiter); ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE); if (unlikely(ret != 0)) goto out; q.bitset = bitset; q.rt_waiter = &rt_waiter; q.requeue_pi_key = &key2; /* * Prepare to wait on uaddr. On success, increments q.key (key1) ref * count. */ ret = futex_wait_setup(uaddr, val, flags, &q, &hb); if (ret) goto out_key2; /* * The check above which compares uaddrs is not sufficient for * shared futexes. We need to compare the keys: */ if (match_futex(&q.key, &key2)) { queue_unlock(hb); ret = -EINVAL; goto out_put_keys; } /* Queue the futex_q, drop the hb lock, wait for wakeup. */ futex_wait_queue_me(hb, &q, to); spin_lock(&hb->lock); ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to); spin_unlock(&hb->lock); if (ret) goto out_put_keys; /* * In order for us to be here, we know our q.key == key2, and since * we took the hb->lock above, we also know that futex_requeue() has * completed and we no longer have to concern ourselves with a wakeup * race with the atomic proxy lock acquisition by the requeue code. The * futex_requeue dropped our key1 reference and incremented our key2 * reference count. */ /* Check if the requeue code acquired the second futex for us. */ if (!q.rt_waiter) { /* * Got the lock. We might not be the anticipated owner if we * did a lock-steal - fix up the PI-state in that case. */ if (q.pi_state && (q.pi_state->owner != current)) { spin_lock(q.lock_ptr); ret = fixup_pi_state_owner(uaddr2, &q, current); if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) { pi_state = q.pi_state; get_pi_state(pi_state); } /* * Drop the reference to the pi state which * the requeue_pi() code acquired for us. */ put_pi_state(q.pi_state); spin_unlock(q.lock_ptr); } } else { struct rt_mutex *pi_mutex; /* * We have been woken up by futex_unlock_pi(), a timeout, or a * signal. futex_unlock_pi() will not destroy the lock_ptr nor * the pi_state. */ WARN_ON(!q.pi_state); pi_mutex = &q.pi_state->pi_mutex; ret = rt_mutex_wait_proxy_lock(pi_mutex, to, &rt_waiter); spin_lock(q.lock_ptr); if (ret && !rt_mutex_cleanup_proxy_lock(pi_mutex, &rt_waiter)) ret = 0; debug_rt_mutex_free_waiter(&rt_waiter); /* * Fixup the pi_state owner and possibly acquire the lock if we * haven't already. */ res = fixup_owner(uaddr2, &q, !ret); /* * If fixup_owner() returned an error, proprogate that. If it * acquired the lock, clear -ETIMEDOUT or -EINTR. */ if (res) ret = (res < 0) ? res : 0; /* * If fixup_pi_state_owner() faulted and was unable to handle * the fault, unlock the rt_mutex and return the fault to * userspace. */ if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) { pi_state = q.pi_state; get_pi_state(pi_state); } /* Unqueue and drop the lock. */ unqueue_me_pi(&q); } if (pi_state) { rt_mutex_futex_unlock(&pi_state->pi_mutex); put_pi_state(pi_state); } if (ret == -EINTR) { /* * We've already been requeued, but cannot restart by calling * futex_lock_pi() directly. We could restart this syscall, but * it would detect that the user space "val" changed and return * -EWOULDBLOCK. Save the overhead of the restart and return * -EWOULDBLOCK directly. */ ret = -EWOULDBLOCK; } out_put_keys: put_futex_key(&q.key); out_key2: put_futex_key(&key2); out: if (to) { hrtimer_cancel(&to->timer); destroy_hrtimer_on_stack(&to->timer); } return ret; } /* * Support for robust futexes: the kernel cleans up held futexes at * thread exit time. * * Implementation: user-space maintains a per-thread list of locks it * is holding. Upon do_exit(), the kernel carefully walks this list, * and marks all locks that are owned by this thread with the * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is * always manipulated with the lock held, so the list is private and * per-thread. Userspace also maintains a per-thread 'list_op_pending' * field, to allow the kernel to clean up if the thread dies after * acquiring the lock, but just before it could have added itself to * the list. There can only be one such pending lock. */ /** * sys_set_robust_list() - Set the robust-futex list head of a task * @head: pointer to the list-head * @len: length of the list-head, as userspace expects */ SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head, size_t, len) { if (!futex_cmpxchg_enabled) return -ENOSYS; /* * The kernel knows only one size for now: */ if (unlikely(len != sizeof(*head))) return -EINVAL; current->robust_list = head; return 0; } /** * sys_get_robust_list() - Get the robust-futex list head of a task * @pid: pid of the process [zero for current task] * @head_ptr: pointer to a list-head pointer, the kernel fills it in * @len_ptr: pointer to a length field, the kernel fills in the header size */ SYSCALL_DEFINE3(get_robust_list, int, pid, struct robust_list_head __user * __user *, head_ptr, size_t __user *, len_ptr) { struct robust_list_head __user *head; unsigned long ret; struct task_struct *p; if (!futex_cmpxchg_enabled) return -ENOSYS; rcu_read_lock(); ret = -ESRCH; if (!pid) p = current; else { p = find_task_by_vpid(pid); if (!p) goto err_unlock; } ret = -EPERM; if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS)) goto err_unlock; head = p->robust_list; rcu_read_unlock(); if (put_user(sizeof(*head), len_ptr)) return -EFAULT; return put_user(head, head_ptr); err_unlock: rcu_read_unlock(); return ret; } /* * Process a futex-list entry, check whether it's owned by the * dying task, and do notification if so: */ static int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi) { u32 uval, uninitialized_var(nval), mval; retry: if (get_user(uval, uaddr)) return -1; if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) { /* * Ok, this dying thread is truly holding a futex * of interest. Set the OWNER_DIED bit atomically * via cmpxchg, and if the value had FUTEX_WAITERS * set, wake up a waiter (if any). (We have to do a * futex_wake() even if OWNER_DIED is already set - * to handle the rare but possible case of recursive * thread-death.) The rest of the cleanup is done in * userspace. */ mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED; /* * We are not holding a lock here, but we want to have * the pagefault_disable/enable() protection because * we want to handle the fault gracefully. If the * access fails we try to fault in the futex with R/W * verification via get_user_pages. get_user() above * does not guarantee R/W access. If that fails we * give up and leave the futex locked. */ if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) { if (fault_in_user_writeable(uaddr)) return -1; goto retry; } if (nval != uval) goto retry; /* * Wake robust non-PI futexes here. The wakeup of * PI futexes happens in exit_pi_state(): */ if (!pi && (uval & FUTEX_WAITERS)) futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY); } return 0; } /* * Fetch a robust-list pointer. Bit 0 signals PI futexes: */ static inline int fetch_robust_entry(struct robust_list __user **entry, struct robust_list __user * __user *head, unsigned int *pi) { unsigned long uentry; if (get_user(uentry, (unsigned long __user *)head)) return -EFAULT; *entry = (void __user *)(uentry & ~1UL); *pi = uentry & 1; return 0; } /* * Walk curr->robust_list (very carefully, it's a userspace list!) * and mark any locks found there dead, and notify any waiters. * * We silently return on any sign of list-walking problem. */ void exit_robust_list(struct task_struct *curr) { struct robust_list_head __user *head = curr->robust_list; struct robust_list __user *entry, *next_entry, *pending; unsigned int limit = ROBUST_LIST_LIMIT, pi, pip; unsigned int uninitialized_var(next_pi); unsigned long futex_offset; int rc; if (!futex_cmpxchg_enabled) return; /* * Fetch the list head (which was registered earlier, via * sys_set_robust_list()): */ if (fetch_robust_entry(&entry, &head->list.next, &pi)) return; /* * Fetch the relative futex offset: */ if (get_user(futex_offset, &head->futex_offset)) return; /* * Fetch any possibly pending lock-add first, and handle it * if it exists: */ if (fetch_robust_entry(&pending, &head->list_op_pending, &pip)) return; next_entry = NULL; /* avoid warning with gcc */ while (entry != &head->list) { /* * Fetch the next entry in the list before calling * handle_futex_death: */ rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi); /* * A pending lock might already be on the list, so * don't process it twice: */ if (entry != pending) if (handle_futex_death((void __user *)entry + futex_offset, curr, pi)) return; if (rc) return; entry = next_entry; pi = next_pi; /* * Avoid excessively long or circular lists: */ if (!--limit) break; cond_resched(); } if (pending) handle_futex_death((void __user *)pending + futex_offset, curr, pip); } long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout, u32 __user *uaddr2, u32 val2, u32 val3) { int cmd = op & FUTEX_CMD_MASK; unsigned int flags = 0; if (!(op & FUTEX_PRIVATE_FLAG)) flags |= FLAGS_SHARED; if (op & FUTEX_CLOCK_REALTIME) { flags |= FLAGS_CLOCKRT; if (cmd != FUTEX_WAIT && cmd != FUTEX_WAIT_BITSET && \ cmd != FUTEX_WAIT_REQUEUE_PI) return -ENOSYS; } switch (cmd) { case FUTEX_LOCK_PI: case FUTEX_UNLOCK_PI: case FUTEX_TRYLOCK_PI: case FUTEX_WAIT_REQUEUE_PI: case FUTEX_CMP_REQUEUE_PI: if (!futex_cmpxchg_enabled) return -ENOSYS; } switch (cmd) { case FUTEX_WAIT: val3 = FUTEX_BITSET_MATCH_ANY; /* fall through */ case FUTEX_WAIT_BITSET: return futex_wait(uaddr, flags, val, timeout, val3); case FUTEX_WAKE: val3 = FUTEX_BITSET_MATCH_ANY; /* fall through */ case FUTEX_WAKE_BITSET: return futex_wake(uaddr, flags, val, val3); case FUTEX_REQUEUE: return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0); case FUTEX_CMP_REQUEUE: return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0); case FUTEX_WAKE_OP: return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3); case FUTEX_LOCK_PI: return futex_lock_pi(uaddr, flags, timeout, 0); case FUTEX_UNLOCK_PI: return futex_unlock_pi(uaddr, flags); case FUTEX_TRYLOCK_PI: return futex_lock_pi(uaddr, flags, NULL, 1); case FUTEX_WAIT_REQUEUE_PI: val3 = FUTEX_BITSET_MATCH_ANY; return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3, uaddr2); case FUTEX_CMP_REQUEUE_PI: return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1); } return -ENOSYS; } SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val, struct __kernel_timespec __user *, utime, u32 __user *, uaddr2, u32, val3) { struct timespec64 ts; ktime_t t, *tp = NULL; u32 val2 = 0; int cmd = op & FUTEX_CMD_MASK; if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI || cmd == FUTEX_WAIT_BITSET || cmd == FUTEX_WAIT_REQUEUE_PI)) { if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG)))) return -EFAULT; if (get_timespec64(&ts, utime)) return -EFAULT; if (!timespec64_valid(&ts)) return -EINVAL; t = timespec64_to_ktime(ts); if (cmd == FUTEX_WAIT) t = ktime_add_safe(ktime_get(), t); tp = &t; } /* * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*. * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP. */ if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE || cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP) val2 = (u32) (unsigned long) utime; return do_futex(uaddr, op, val, tp, uaddr2, val2, val3); } #ifdef CONFIG_COMPAT /* * Fetch a robust-list pointer. Bit 0 signals PI futexes: */ static inline int compat_fetch_robust_entry(compat_uptr_t *uentry, struct robust_list __user **entry, compat_uptr_t __user *head, unsigned int *pi) { if (get_user(*uentry, head)) return -EFAULT; *entry = compat_ptr((*uentry) & ~1); *pi = (unsigned int)(*uentry) & 1; return 0; } static void __user *futex_uaddr(struct robust_list __user *entry, compat_long_t futex_offset) { compat_uptr_t base = ptr_to_compat(entry); void __user *uaddr = compat_ptr(base + futex_offset); return uaddr; } /* * Walk curr->robust_list (very carefully, it's a userspace list!) * and mark any locks found there dead, and notify any waiters. * * We silently return on any sign of list-walking problem. */ void compat_exit_robust_list(struct task_struct *curr) { struct compat_robust_list_head __user *head = curr->compat_robust_list; struct robust_list __user *entry, *next_entry, *pending; unsigned int limit = ROBUST_LIST_LIMIT, pi, pip; unsigned int uninitialized_var(next_pi); compat_uptr_t uentry, next_uentry, upending; compat_long_t futex_offset; int rc; if (!futex_cmpxchg_enabled) return; /* * Fetch the list head (which was registered earlier, via * sys_set_robust_list()): */ if (compat_fetch_robust_entry(&uentry, &entry, &head->list.next, &pi)) return; /* * Fetch the relative futex offset: */ if (get_user(futex_offset, &head->futex_offset)) return; /* * Fetch any possibly pending lock-add first, and handle it * if it exists: */ if (compat_fetch_robust_entry(&upending, &pending, &head->list_op_pending, &pip)) return; next_entry = NULL; /* avoid warning with gcc */ while (entry != (struct robust_list __user *) &head->list) { /* * Fetch the next entry in the list before calling * handle_futex_death: */ rc = compat_fetch_robust_entry(&next_uentry, &next_entry, (compat_uptr_t __user *)&entry->next, &next_pi); /* * A pending lock might already be on the list, so * dont process it twice: */ if (entry != pending) { void __user *uaddr = futex_uaddr(entry, futex_offset); if (handle_futex_death(uaddr, curr, pi)) return; } if (rc) return; uentry = next_uentry; entry = next_entry; pi = next_pi; /* * Avoid excessively long or circular lists: */ if (!--limit) break; cond_resched(); } if (pending) { void __user *uaddr = futex_uaddr(pending, futex_offset); handle_futex_death(uaddr, curr, pip); } } COMPAT_SYSCALL_DEFINE2(set_robust_list, struct compat_robust_list_head __user *, head, compat_size_t, len) { if (!futex_cmpxchg_enabled) return -ENOSYS; if (unlikely(len != sizeof(*head))) return -EINVAL; current->compat_robust_list = head; return 0; } COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid, compat_uptr_t __user *, head_ptr, compat_size_t __user *, len_ptr) { struct compat_robust_list_head __user *head; unsigned long ret; struct task_struct *p; if (!futex_cmpxchg_enabled) return -ENOSYS; rcu_read_lock(); ret = -ESRCH; if (!pid) p = current; else { p = find_task_by_vpid(pid); if (!p) goto err_unlock; } ret = -EPERM; if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS)) goto err_unlock; head = p->compat_robust_list; rcu_read_unlock(); if (put_user(sizeof(*head), len_ptr)) return -EFAULT; return put_user(ptr_to_compat(head), head_ptr); err_unlock: rcu_read_unlock(); return ret; } #endif /* CONFIG_COMPAT */ #ifdef CONFIG_COMPAT_32BIT_TIME COMPAT_SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val, struct old_timespec32 __user *, utime, u32 __user *, uaddr2, u32, val3) { struct timespec64 ts; ktime_t t, *tp = NULL; int val2 = 0; int cmd = op & FUTEX_CMD_MASK; if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI || cmd == FUTEX_WAIT_BITSET || cmd == FUTEX_WAIT_REQUEUE_PI)) { if (get_old_timespec32(&ts, utime)) return -EFAULT; if (!timespec64_valid(&ts)) return -EINVAL; t = timespec64_to_ktime(ts); if (cmd == FUTEX_WAIT) t = ktime_add_safe(ktime_get(), t); tp = &t; } if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE || cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP) val2 = (int) (unsigned long) utime; return do_futex(uaddr, op, val, tp, uaddr2, val2, val3); } #endif /* CONFIG_COMPAT_32BIT_TIME */ static void __init futex_detect_cmpxchg(void) { #ifndef CONFIG_HAVE_FUTEX_CMPXCHG u32 curval; /* * This will fail and we want it. Some arch implementations do * runtime detection of the futex_atomic_cmpxchg_inatomic() * functionality. We want to know that before we call in any * of the complex code paths. Also we want to prevent * registration of robust lists in that case. NULL is * guaranteed to fault and we get -EFAULT on functional * implementation, the non-functional ones will return * -ENOSYS. */ if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT) futex_cmpxchg_enabled = 1; #endif } static int __init futex_init(void) { unsigned int futex_shift; unsigned long i; #if CONFIG_BASE_SMALL futex_hashsize = 16; #else futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus()); #endif futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues), futex_hashsize, 0, futex_hashsize < 256 ? HASH_SMALL : 0, &futex_shift, NULL, futex_hashsize, futex_hashsize); futex_hashsize = 1UL << futex_shift; futex_detect_cmpxchg(); for (i = 0; i < futex_hashsize; i++) { atomic_set(&futex_queues[i].waiters, 0); plist_head_init(&futex_queues[i].chain); spin_lock_init(&futex_queues[i].lock); } return 0; } core_initcall(futex_init);
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