Release 4.13 ipc/sem.c
/*
* linux/ipc/sem.c
* Copyright (C) 1992 Krishna Balasubramanian
* Copyright (C) 1995 Eric Schenk, Bruno Haible
*
* /proc/sysvipc/sem support (c) 1999 Dragos Acostachioaie <dragos@iname.com>
*
* SMP-threaded, sysctl's added
* (c) 1999 Manfred Spraul <manfred@colorfullife.com>
* Enforced range limit on SEM_UNDO
* (c) 2001 Red Hat Inc
* Lockless wakeup
* (c) 2003 Manfred Spraul <manfred@colorfullife.com>
* (c) 2016 Davidlohr Bueso <dave@stgolabs.net>
* Further wakeup optimizations, documentation
* (c) 2010 Manfred Spraul <manfred@colorfullife.com>
*
* support for audit of ipc object properties and permission changes
* Dustin Kirkland <dustin.kirkland@us.ibm.com>
*
* namespaces support
* OpenVZ, SWsoft Inc.
* Pavel Emelianov <xemul@openvz.org>
*
* Implementation notes: (May 2010)
* This file implements System V semaphores.
*
* User space visible behavior:
* - FIFO ordering for semop() operations (just FIFO, not starvation
* protection)
* - multiple semaphore operations that alter the same semaphore in
* one semop() are handled.
* - sem_ctime (time of last semctl()) is updated in the IPC_SET, SETVAL and
* SETALL calls.
* - two Linux specific semctl() commands: SEM_STAT, SEM_INFO.
* - undo adjustments at process exit are limited to 0..SEMVMX.
* - namespace are supported.
* - SEMMSL, SEMMNS, SEMOPM and SEMMNI can be configured at runtine by writing
* to /proc/sys/kernel/sem.
* - statistics about the usage are reported in /proc/sysvipc/sem.
*
* Internals:
* - scalability:
* - all global variables are read-mostly.
* - semop() calls and semctl(RMID) are synchronized by RCU.
* - most operations do write operations (actually: spin_lock calls) to
* the per-semaphore array structure.
* Thus: Perfect SMP scaling between independent semaphore arrays.
* If multiple semaphores in one array are used, then cache line
* trashing on the semaphore array spinlock will limit the scaling.
* - semncnt and semzcnt are calculated on demand in count_semcnt()
* - the task that performs a successful semop() scans the list of all
* sleeping tasks and completes any pending operations that can be fulfilled.
* Semaphores are actively given to waiting tasks (necessary for FIFO).
* (see update_queue())
* - To improve the scalability, the actual wake-up calls are performed after
* dropping all locks. (see wake_up_sem_queue_prepare())
* - All work is done by the waker, the woken up task does not have to do
* anything - not even acquiring a lock or dropping a refcount.
* - A woken up task may not even touch the semaphore array anymore, it may
* have been destroyed already by a semctl(RMID).
* - UNDO values are stored in an array (one per process and per
* semaphore array, lazily allocated). For backwards compatibility, multiple
* modes for the UNDO variables are supported (per process, per thread)
* (see copy_semundo, CLONE_SYSVSEM)
* - There are two lists of the pending operations: a per-array list
* and per-semaphore list (stored in the array). This allows to achieve FIFO
* ordering without always scanning all pending operations.
* The worst-case behavior is nevertheless O(N^2) for N wakeups.
*/
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/init.h>
#include <linux/proc_fs.h>
#include <linux/time.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/audit.h>
#include <linux/capability.h>
#include <linux/seq_file.h>
#include <linux/rwsem.h>
#include <linux/nsproxy.h>
#include <linux/ipc_namespace.h>
#include <linux/sched/wake_q.h>
#include <linux/uaccess.h>
#include "util.h"
/* One queue for each sleeping process in the system. */
struct sem_queue {
struct list_head list; /* queue of pending operations */
struct task_struct *sleeper; /* this process */
struct sem_undo *undo; /* undo structure */
int pid; /* process id of requesting process */
int status; /* completion status of operation */
struct sembuf *sops; /* array of pending operations */
struct sembuf *blocking; /* the operation that blocked */
int nsops; /* number of operations */
bool alter; /* does *sops alter the array? */
bool dupsop; /* sops on more than one sem_num */
};
/* Each task has a list of undo requests. They are executed automatically
* when the process exits.
*/
struct sem_undo {
struct list_head list_proc; /* per-process list: *
* all undos from one process
* rcu protected */
struct rcu_head rcu; /* rcu struct for sem_undo */
struct sem_undo_list *ulp; /* back ptr to sem_undo_list */
struct list_head list_id; /* per semaphore array list:
* all undos for one array */
int semid; /* semaphore set identifier */
short *semadj; /* array of adjustments */
/* one per semaphore */
};
/* sem_undo_list controls shared access to the list of sem_undo structures
* that may be shared among all a CLONE_SYSVSEM task group.
*/
struct sem_undo_list {
atomic_t refcnt;
spinlock_t lock;
struct list_head list_proc;
};
#define sem_ids(ns) ((ns)->ids[IPC_SEM_IDS])
#define sem_checkid(sma, semid) ipc_checkid(&sma->sem_perm, semid)
static int newary(struct ipc_namespace *, struct ipc_params *);
static void freeary(struct ipc_namespace *, struct kern_ipc_perm *);
#ifdef CONFIG_PROC_FS
static int sysvipc_sem_proc_show(struct seq_file *s, void *it);
#endif
#define SEMMSL_FAST 256
/* 512 bytes on stack */
#define SEMOPM_FAST 64
/* ~ 372 bytes on stack */
/*
* Switching from the mode suitable for simple ops
* to the mode for complex ops is costly. Therefore:
* use some hysteresis
*/
#define USE_GLOBAL_LOCK_HYSTERESIS 10
/*
* Locking:
* a) global sem_lock() for read/write
* sem_undo.id_next,
* sem_array.complex_count,
* sem_array.pending{_alter,_const},
* sem_array.sem_undo
*
* b) global or semaphore sem_lock() for read/write:
* sem_array.sems[i].pending_{const,alter}:
*
* c) special:
* sem_undo_list.list_proc:
* * undo_list->lock for write
* * rcu for read
* use_global_lock:
* * global sem_lock() for write
* * either local or global sem_lock() for read.
*
* Memory ordering:
* Most ordering is enforced by using spin_lock() and spin_unlock().
* The special case is use_global_lock:
* Setting it from non-zero to 0 is a RELEASE, this is ensured by
* using smp_store_release().
* Testing if it is non-zero is an ACQUIRE, this is ensured by using
* smp_load_acquire().
* Setting it from 0 to non-zero must be ordered with regards to
* this smp_load_acquire(), this is guaranteed because the smp_load_acquire()
* is inside a spin_lock() and after a write from 0 to non-zero a
* spin_lock()+spin_unlock() is done.
*/
#define sc_semmsl sem_ctls[0]
#define sc_semmns sem_ctls[1]
#define sc_semopm sem_ctls[2]
#define sc_semmni sem_ctls[3]
void sem_init_ns(struct ipc_namespace *ns)
{
ns->sc_semmsl = SEMMSL;
ns->sc_semmns = SEMMNS;
ns->sc_semopm = SEMOPM;
ns->sc_semmni = SEMMNI;
ns->used_sems = 0;
ipc_init_ids(&ns->ids[IPC_SEM_IDS]);
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Kirill Korotaev | 43 | 84.31% | 1 | 33.33% |
| Pierre Peiffer | 7 | 13.73% | 1 | 33.33% |
| Linus Torvalds (pre-git) | 1 | 1.96% | 1 | 33.33% |
| Total | 51 | 100.00% | 3 | 100.00% |
#ifdef CONFIG_IPC_NS
void sem_exit_ns(struct ipc_namespace *ns)
{
free_ipcs(ns, &sem_ids(ns), freeary);
idr_destroy(&ns->ids[IPC_SEM_IDS].ipcs_idr);
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Kirill Korotaev | 14 | 38.89% | 1 | 16.67% |
| Serge E. Hallyn | 13 | 36.11% | 1 | 16.67% |
| Linus Torvalds (pre-git) | 4 | 11.11% | 2 | 33.33% |
| Nadia Derbey | 3 | 8.33% | 1 | 16.67% |
| Pierre Peiffer | 2 | 5.56% | 1 | 16.67% |
| Total | 36 | 100.00% | 6 | 100.00% |
#endif
void __init sem_init(void)
{
sem_init_ns(&init_ipc_ns);
ipc_init_proc_interface("sysvipc/sem",
" key semid perms nsems uid gid cuid cgid otime ctime\n",
IPC_SEM_IDS, sysvipc_sem_proc_show);
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Kirill Korotaev | 11 | 44.00% | 1 | 14.29% |
| Linus Torvalds (pre-git) | 10 | 40.00% | 4 | 57.14% |
| Mike Waychison | 3 | 12.00% | 1 | 14.29% |
| Pierre Peiffer | 1 | 4.00% | 1 | 14.29% |
| Total | 25 | 100.00% | 7 | 100.00% |
/**
* unmerge_queues - unmerge queues, if possible.
* @sma: semaphore array
*
* The function unmerges the wait queues if complex_count is 0.
* It must be called prior to dropping the global semaphore array lock.
*/
static void unmerge_queues(struct sem_array *sma)
{
struct sem_queue *q, *tq;
/* complex operations still around? */
if (sma->complex_count)
return;
/*
* We will switch back to simple mode.
* Move all pending operation back into the per-semaphore
* queues.
*/
list_for_each_entry_safe(q, tq, &sma->pending_alter, list) {
struct sem *curr;
curr = &sma->sems[q->sops[0].sem_num];
list_add_tail(&q->list, &curr->pending_alter);
}
INIT_LIST_HEAD(&sma->pending_alter);
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Manfred Spraul | 83 | 100.00% | 2 | 100.00% |
| Total | 83 | 100.00% | 2 | 100.00% |
/**
* merge_queues - merge single semop queues into global queue
* @sma: semaphore array
*
* This function merges all per-semaphore queues into the global queue.
* It is necessary to achieve FIFO ordering for the pending single-sop
* operations when a multi-semop operation must sleep.
* Only the alter operations must be moved, the const operations can stay.
*/
static void merge_queues(struct sem_array *sma)
{
int i;
for (i = 0; i < sma->sem_nsems; i++) {
struct sem *sem = &sma->sems[i];
list_splice_init(&sem->pending_alter, &sma->pending_alter);
}
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Manfred Spraul | 57 | 100.00% | 2 | 100.00% |
| Total | 57 | 100.00% | 2 | 100.00% |
static void sem_rcu_free(struct rcu_head *head)
{
struct kern_ipc_perm *p = container_of(head, struct kern_ipc_perm, rcu);
struct sem_array *sma = container_of(p, struct sem_array, sem_perm);
security_sem_free(sma);
kvfree(sma);
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Davidlohr Bueso A | 41 | 80.39% | 1 | 25.00% |
| Manfred Spraul | 8 | 15.69% | 1 | 25.00% |
| Kees Cook | 2 | 3.92% | 2 | 50.00% |
| Total | 51 | 100.00% | 4 | 100.00% |
/*
* Enter the mode suitable for non-simple operations:
* Caller must own sem_perm.lock.
*/
static void complexmode_enter(struct sem_array *sma)
{
int i;
struct sem *sem;
if (sma->use_global_lock > 0) {
/*
* We are already in global lock mode.
* Nothing to do, just reset the
* counter until we return to simple mode.
*/
sma->use_global_lock = USE_GLOBAL_LOCK_HYSTERESIS;
return;
}
sma->use_global_lock = USE_GLOBAL_LOCK_HYSTERESIS;
for (i = 0; i < sma->sem_nsems; i++) {
sem = &sma->sems[i];
spin_lock(&sem->lock);
spin_unlock(&sem->lock);
}
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Manfred Spraul | 86 | 100.00% | 6 | 100.00% |
| Total | 86 | 100.00% | 6 | 100.00% |
/*
* Try to leave the mode that disallows simple operations:
* Caller must own sem_perm.lock.
*/
static void complexmode_tryleave(struct sem_array *sma)
{
if (sma->complex_count) {
/* Complex ops are sleeping.
* We must stay in complex mode
*/
return;
}
if (sma->use_global_lock == 1) {
/*
* Immediately after setting use_global_lock to 0,
* a simple op can start. Thus: all memory writes
* performed by the current operation must be visible
* before we set use_global_lock to 0.
*/
smp_store_release(&sma->use_global_lock, 0);
} else {
sma->use_global_lock--;
}
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Manfred Spraul | 50 | 100.00% | 2 | 100.00% |
| Total | 50 | 100.00% | 2 | 100.00% |
#define SEM_GLOBAL_LOCK (-1)
/*
* If the request contains only one semaphore operation, and there are
* no complex transactions pending, lock only the semaphore involved.
* Otherwise, lock the entire semaphore array, since we either have
* multiple semaphores in our own semops, or we need to look at
* semaphores from other pending complex operations.
*/
static inline int sem_lock(struct sem_array *sma, struct sembuf *sops,
int nsops)
{
struct sem *sem;
if (nsops != 1) {
/* Complex operation - acquire a full lock */
ipc_lock_object(&sma->sem_perm);
/* Prevent parallel simple ops */
complexmode_enter(sma);
return SEM_GLOBAL_LOCK;
}
/*
* Only one semaphore affected - try to optimize locking.
* Optimized locking is possible if no complex operation
* is either enqueued or processed right now.
*
* Both facts are tracked by use_global_mode.
*/
sem = &sma->sems[sops->sem_num];
/*
* Initial check for use_global_lock. Just an optimization,
* no locking, no memory barrier.
*/
if (!sma->use_global_lock) {
/*
* It appears that no complex operation is around.
* Acquire the per-semaphore lock.
*/
spin_lock(&sem->lock);
/* pairs with smp_store_release() */
if (!smp_load_acquire(&sma->use_global_lock)) {
/* fast path successful! */
return sops->sem_num;
}
spin_unlock(&sem->lock);
}
/* slow path: acquire the full lock */
ipc_lock_object(&sma->sem_perm);
if (sma->use_global_lock == 0) {
/*
* The use_global_lock mode ended while we waited for
* sma->sem_perm.lock. Thus we must switch to locking
* with sem->lock.
* Unlike in the fast path, there is no need to recheck
* sma->use_global_lock after we have acquired sem->lock:
* We own sma->sem_perm.lock, thus use_global_lock cannot
* change.
*/
spin_lock(&sem->lock);
ipc_unlock_object(&sma->sem_perm);
return sops->sem_num;
} else {
/*
* Not a false alarm, thus continue to use the global lock
* mode. No need for complexmode_enter(), this was done by
* the caller that has set use_global_mode to non-zero.
*/
return SEM_GLOBAL_LOCK;
}
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Manfred Spraul | 76 | 47.80% | 4 | 50.00% |
| Rik Van Riel | 67 | 42.14% | 2 | 25.00% |
| Nadia Derbey | 13 | 8.18% | 1 | 12.50% |
| Pierre Peiffer | 3 | 1.89% | 1 | 12.50% |
| Total | 159 | 100.00% | 8 | 100.00% |
static inline void sem_unlock(struct sem_array *sma, int locknum)
{
if (locknum == SEM_GLOBAL_LOCK) {
unmerge_queues(sma);
complexmode_tryleave(sma);
ipc_unlock_object(&sma->sem_perm);
} else {
struct sem *sem = &sma->sems[locknum];
spin_unlock(&sem->lock);
}
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Rik Van Riel | 48 | 73.85% | 2 | 28.57% |
| Manfred Spraul | 15 | 23.08% | 3 | 42.86% |
| Nadia Derbey | 1 | 1.54% | 1 | 14.29% |
| Davidlohr Bueso A | 1 | 1.54% | 1 | 14.29% |
| Total | 65 | 100.00% | 7 | 100.00% |
/*
* sem_lock_(check_) routines are called in the paths where the rwsem
* is not held.
*
* The caller holds the RCU read lock.
*/
static inline struct sem_array *sem_obtain_object(struct ipc_namespace *ns, int id)
{
struct kern_ipc_perm *ipcp = ipc_obtain_object_idr(&sem_ids(ns), id);
if (IS_ERR(ipcp))
return ERR_CAST(ipcp);
return container_of(ipcp, struct sem_array, sem_perm);
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Nadia Derbey | 30 | 52.63% | 2 | 33.33% |
| Davidlohr Bueso A | 16 | 28.07% | 2 | 33.33% |
| Pierre Peiffer | 10 | 17.54% | 1 | 16.67% |
| Rik Van Riel | 1 | 1.75% | 1 | 16.67% |
| Total | 57 | 100.00% | 6 | 100.00% |
static inline struct sem_array *sem_obtain_object_check(struct ipc_namespace *ns,
int id)
{
struct kern_ipc_perm *ipcp = ipc_obtain_object_check(&sem_ids(ns), id);
if (IS_ERR(ipcp))
return ERR_CAST(ipcp);
return container_of(ipcp, struct sem_array, sem_perm);
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Davidlohr Bueso A | 43 | 75.44% | 1 | 25.00% |
| Nadia Derbey | 12 | 21.05% | 2 | 50.00% |
| Pierre Peiffer | 2 | 3.51% | 1 | 25.00% |
| Total | 57 | 100.00% | 4 | 100.00% |
static inline void sem_lock_and_putref(struct sem_array *sma)
{
sem_lock(sma, NULL, -1);
ipc_rcu_putref(&sma->sem_perm, sem_rcu_free);
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Pierre Peiffer | 21 | 65.62% | 1 | 20.00% |
| Rik Van Riel | 6 | 18.75% | 1 | 20.00% |
| Manfred Spraul | 3 | 9.38% | 1 | 20.00% |
| Fabian Frederick | 1 | 3.12% | 1 | 20.00% |
| Davidlohr Bueso A | 1 | 3.12% | 1 | 20.00% |
| Total | 32 | 100.00% | 5 | 100.00% |
static inline void sem_rmid(struct ipc_namespace *ns, struct sem_array *s)
{
ipc_rmid(&sem_ids(ns), &s->sem_perm);
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Nadia Derbey | 31 | 100.00% | 1 | 100.00% |
| Total | 31 | 100.00% | 1 | 100.00% |
static struct sem_array *sem_alloc(size_t nsems)
{
struct sem_array *sma;
size_t size;
if (nsems > (INT_MAX - sizeof(*sma)) / sizeof(sma->sems[0]))
return NULL;
size = sizeof(*sma) + nsems * sizeof(sma->sems[0]);
sma = kvmalloc(size, GFP_KERNEL);
if (unlikely(!sma))
return NULL;
memset(sma, 0, size);
return sma;
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Kees Cook | 98 | 100.00% | 1 | 100.00% |
| Total | 98 | 100.00% | 1 | 100.00% |
/**
* newary - Create a new semaphore set
* @ns: namespace
* @params: ptr to the structure that contains key, semflg and nsems
*
* Called with sem_ids.rwsem held (as a writer)
*/
static int newary(struct ipc_namespace *ns, struct ipc_params *params)
{
int retval;
struct sem_array *sma;
key_t key = params->key;
int nsems = params->u.nsems;
int semflg = params->flg;
int i;
if (!nsems)
return -EINVAL;
if (ns->used_sems + nsems > ns->sc_semmns)
return -ENOSPC;
sma = sem_alloc(nsems);
if (!sma)
return -ENOMEM;
sma->sem_perm.mode = (semflg & S_IRWXUGO);
sma->sem_perm.key = key;
sma->sem_perm.security = NULL;
retval = security_sem_alloc(sma);
if (retval) {
kvfree(sma);
return retval;
}
for (i = 0; i < nsems; i++) {
INIT_LIST_HEAD(&sma->sems[i].pending_alter);
INIT_LIST_HEAD(&sma->sems[i].pending_const);
spin_lock_init(&sma->sems[i].lock);
}
sma->complex_count = 0;
sma->use_global_lock = USE_GLOBAL_LOCK_HYSTERESIS;
INIT_LIST_HEAD(&sma->pending_alter);
INIT_LIST_HEAD(&sma->pending_const);
INIT_LIST_HEAD(&sma->list_id);
sma->sem_nsems = nsems;
sma->sem_ctime = get_seconds();
retval = ipc_addid(&sem_ids(ns), &sma->sem_perm, ns->sc_semmni);
if (retval < 0) {
call_rcu(&sma->sem_perm.rcu, sem_rcu_free);
return retval;
}
ns->used_sems += nsems;
sem_unlock(sma, -1);
rcu_read_unlock();
return sma->sem_perm.id;
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Manfred Spraul | 126 | 40.65% | 10 | 34.48% |
| Linus Torvalds (pre-git) | 69 | 22.26% | 6 | 20.69% |
| Nadia Derbey | 30 | 9.68% | 2 | 6.90% |
| Stephen D. Smalley | 25 | 8.06% | 1 | 3.45% |
| Greg Kroah-Hartman | 25 | 8.06% | 3 | 10.34% |
| Rik Van Riel | 17 | 5.48% | 1 | 3.45% |
| Kirill Korotaev | 9 | 2.90% | 1 | 3.45% |
| Kees Cook | 3 | 0.97% | 2 | 6.90% |
| Linus Torvalds | 3 | 0.97% | 1 | 3.45% |
| Andi Kleen | 2 | 0.65% | 1 | 3.45% |
| Andrew Morton | 1 | 0.32% | 1 | 3.45% |
| Total | 310 | 100.00% | 29 | 100.00% |
/*
* Called with sem_ids.rwsem and ipcp locked.
*/
static inline int sem_security(struct kern_ipc_perm *ipcp, int semflg)
{
struct sem_array *sma;
sma = container_of(ipcp, struct sem_array, sem_perm);
return security_sem_associate(sma, semflg);
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Nadia Derbey | 40 | 100.00% | 2 | 100.00% |
| Total | 40 | 100.00% | 2 | 100.00% |
/*
* Called with sem_ids.rwsem and ipcp locked.
*/
static inline int sem_more_checks(struct kern_ipc_perm *ipcp,
struct ipc_params *params)
{
struct sem_array *sma;
sma = container_of(ipcp, struct sem_array, sem_perm);
if (params->u.nsems > sma->sem_nsems)
return -EINVAL;
return 0;
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Nadia Derbey | 53 | 100.00% | 2 | 100.00% |
| Total | 53 | 100.00% | 2 | 100.00% |
SYSCALL_DEFINE3(semget, key_t, key, int, nsems, int, semflg)
{
struct ipc_namespace *ns;
static const struct ipc_ops sem_ops = {
.getnew = newary,
.associate = sem_security,
.more_checks = sem_more_checks,
};
struct ipc_params sem_params;
ns = current->nsproxy->ipc_ns;
if (nsems < 0 || nsems > ns->sc_semmsl)
return -EINVAL;
sem_params.key = key;
sem_params.flg = semflg;
sem_params.u.nsems = nsems;
return ipcget(ns, &sem_ids(ns), &sem_ops, &sem_params);
}
/**
* perform_atomic_semop[_slow] - Attempt to perform semaphore
* operations on a given array.
* @sma: semaphore array
* @q: struct sem_queue that describes the operation
*
* Caller blocking are as follows, based the value
* indicated by the semaphore operation (sem_op):
*
* (1) >0 never blocks.
* (2) 0 (wait-for-zero operation): semval is non-zero.
* (3) <0 attempting to decrement semval to a value smaller than zero.
*
* Returns 0 if the operation was possible.
* Returns 1 if the operation is impossible, the caller must sleep.
* Returns <0 for error codes.
*/
static int perform_atomic_semop_slow(struct sem_array *sma, struct sem_queue *q)
{
int result, sem_op, nsops, pid;
struct sembuf *sop;
struct sem *curr;
struct sembuf *sops;
struct sem_undo *un;
sops = q->sops;
nsops = q->nsops;
un = q->undo;
for (sop = sops; sop < sops + nsops; sop++) {
curr = &sma->sems[sop->sem_num];
sem_op = sop->sem_op;
result = curr->semval;
if (!sem_op && result)
goto would_block;
result += sem_op;
if (result < 0)
goto would_block;
if (result > SEMVMX)
goto out_of_range;
if (sop->sem_flg & SEM_UNDO) {
int undo = un->semadj[sop->sem_num] - sem_op;
/* Exceeding the undo range is an error. */
if (undo < (-SEMAEM - 1) || undo > SEMAEM)
goto out_of_range;
un->semadj[sop->sem_num] = undo;
}
curr->semval = result;
}
sop--;
pid = q->pid;
while (sop >= sops) {
sma->sems[sop->sem_num].sempid = pid;
sop--;
}
return 0;
out_of_range:
result = -ERANGE;
goto undo;
would_block:
q->blocking = sop;
if (sop->sem_flg & IPC_NOWAIT)
result = -EAGAIN;
else
result = 1;
undo:
sop--;
while (sop >= sops) {
sem_op = sop->sem_op;
sma->sems[sop->sem_num].semval -= sem_op;
if (sop->sem_flg & SEM_UNDO)
un->semadj[sop->sem_num] += sem_op;
sop--;
}
return result;
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Linus Torvalds (pre-git) | 152 | 46.77% | 4 | 36.36% |
| Andrew Morton | 57 | 17.54% | 1 | 9.09% |
| Manfred Spraul | 52 | 16.00% | 3 | 27.27% |
| Petr Mladek | 35 | 10.77% | 1 | 9.09% |
| Linus Torvalds | 28 | 8.62% | 1 | 9.09% |
| Davidlohr Bueso A | 1 | 0.31% | 1 | 9.09% |
| Total | 325 | 100.00% | 11 | 100.00% |
static int perform_atomic_semop(struct sem_array *sma, struct sem_queue *q)
{
int result, sem_op, nsops;
struct sembuf *sop;
struct sem *curr;
struct sembuf *sops;
struct sem_undo *un;
sops = q->sops;
nsops = q->nsops;
un = q->undo;
if (unlikely(q->dupsop))
return perform_atomic_semop_slow(sma, q);
/*
* We scan the semaphore set twice, first to ensure that the entire
* operation can succeed, therefore avoiding any pointless writes
* to shared memory and having to undo such changes in order to block
* until the operations can go through.
*/
for (sop = sops; sop < sops + nsops; sop++) {
curr = &sma->sems[sop->sem_num];
sem_op = sop->sem_op;
result = curr->semval;
if (!sem_op && result)
goto would_block; /* wait-for-zero */
result += sem_op;
if (result < 0)
goto would_block;
if (result > SEMVMX)
return -ERANGE;
if (sop->sem_flg & SEM_UNDO) {
int undo = un->semadj[sop->sem_num] - sem_op;
/* Exceeding the undo range is an error. */
if (undo < (-SEMAEM - 1) || undo > SEMAEM)
return -ERANGE;
}
}
for (sop = sops; sop < sops + nsops; sop++) {
curr = &sma->sems[sop->sem_num];
sem_op = sop->sem_op;
result = curr->semval;
if (sop->sem_flg & SEM_UNDO) {
int undo = un->semadj[sop->sem_num] - sem_op;
un->semadj[sop->sem_num] = undo;
}
curr->semval += sem_op;
curr->sempid = q->pid;
}
return 0;
would_block:
q->blocking = sop;
return sop->sem_flg & IPC_NOWAIT ? -EAGAIN : 1;
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Davidlohr Bueso A | 303 | 97.43% | 1 | 50.00% |
| Manfred Spraul | 8 | 2.57% | 1 | 50.00% |
| Total | 311 | 100.00% | 2 | 100.00% |
static inline void wake_up_sem_queue_prepare(struct sem_queue *q, int error,
struct wake_q_head *wake_q)
{
wake_q_add(wake_q, q->sleeper);
/*
* Rely on the above implicit barrier, such that we can
* ensure that we hold reference to the task before setting
* q->status. Otherwise we could race with do_exit if the
* task is awoken by an external event before calling
* wake_up_process().
*/
WRITE_ONCE(q->status, error);
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Nicholas Piggin | 20 | 51.28% | 1 | 33.33% |
| Davidlohr Bueso A | 12 | 30.77% | 1 | 33.33% |
| Manfred Spraul | 7 | 17.95% | 1 | 33.33% |
| Total | 39 | 100.00% | 3 | 100.00% |
static void unlink_queue(struct sem_array *sma, struct sem_queue *q)
{
list_del(&q->list);
if (q->nsops > 1)
sma->complex_count--;
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Manfred Spraul | 36 | 97.30% | 1 | 50.00% |
| Rik Van Riel | 1 | 2.70% | 1 | 50.00% |
| Total | 37 | 100.00% | 2 | 100.00% |
/** check_restart(sma, q)
* @sma: semaphore array
* @q: the operation that just completed
*
* update_queue is O(N^2) when it restarts scanning the whole queue of
* waiting operations. Therefore this function checks if the restart is
* really necessary. It is called after a previously waiting operation
* modified the array.
* Note that wait-for-zero operations are handled without restart.
*/
static inline int check_restart(struct sem_array *sma, struct sem_queue *q)
{
/* pending complex alter operations are too difficult to analyse */
if (!list_empty(&sma->pending_alter))
return 1;
/* we were a sleeping complex operation. Too difficult */
if (q->nsops > 1)
return 1;
/* It is impossible that someone waits for the new value:
* - complex operations always restart.
* - wait-for-zero are handled seperately.
* - q is a previously sleeping simple operation that
* altered the array. It must be a decrement, because
* simple increments never sleep.
* - If there are older (higher priority) decrements
* in the queue, then they have observed the original
* semval value and couldn't proceed. The operation
* decremented to value - thus they won't proceed either.
*/
return 0;
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Manfred Spraul | 47 | 97.92% | 2 | 66.67% |
| Davidlohr Bueso A | 1 | 2.08% | 1 | 33.33% |
| Total | 48 | 100.00% | 3 | 100.00% |
/**
* wake_const_ops - wake up non-alter tasks
* @sma: semaphore array.
* @semnum: semaphore that was modified.
* @wake_q: lockless wake-queue head.
*
* wake_const_ops must be called after a semaphore in a semaphore array
* was set to 0. If complex const operations are pending, wake_const_ops must
* be called with semnum = -1, as well as with the number of each modified
* semaphore.
* The tasks that must be woken up are added to @wake_q. The return code
* is stored in q->pid.
* The function returns 1 if at least one operation was completed successfully.
*/
static int wake_const_ops(struct sem_array *sma, int semnum,
struct wake_q_head *wake_q)
{
struct sem_queue *q, *tmp;
struct list_head *pending_list;
int semop_completed = 0;
if (semnum == -1)
pending_list = &sma->pending_const;
else
pending_list = &sma->sems[semnum].pending_const;
list_for_each_entry_safe(q, tmp, pending_list, list) {
int error = perform_atomic_semop(sma, q);
if (error > 0)
continue;
/* operation completed, remove from queue & wakeup */
unlink_queue(sma, q);
wake_up_sem_queue_prepare(q, error, wake_q);
if (error == 0)
semop_completed = 1;
}
return semop_completed;
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Manfred Spraul | 105 | 85.37% | 4 | 66.67% |
| Davidlohr Bueso A | 18 | 14.63% | 2 | 33.33% |
| Total | 123 | 100.00% | 6 | 100.00% |
/**
* do_smart_wakeup_zero - wakeup all wait for zero tasks
* @sma: semaphore array
* @sops: operations that were performed
* @nsops: number of operations
* @wake_q: lockless wake-queue head
*
* Checks all required queue for wait-for-zero operations, based
* on the actual changes that were performed on the semaphore array.
* The function returns 1 if at least one operation was completed successfully.
*/
static int do_smart_wakeup_zero(struct sem_array *sma, struct sembuf *sops,
int nsops, struct wake_q_head *wake_q)
{
int i;
int semop_completed = 0;
int got_zero = 0;
/* first: the per-semaphore queues, if known */
if (sops) {
for (i = 0; i < nsops; i++) {
int num = sops[i].sem_num;
if (sma->sems[num].semval == 0) {
got_zero = 1;
semop_completed |= wake_const_ops(sma, num, wake_q);
}
}
} else {
/*
* No sops means modified semaphores not known.
* Assume all were changed.
*/
for (i = 0; i < sma->sem_nsems; i++) {
if (sma->sems[i].semval == 0) {
got_zero = 1;
semop_completed |= wake_const_ops(sma, i, wake_q);
}
}
}
/*
* If one of the modified semaphores got 0,
* then check the global queue, too.
*/
if (got_zero