cregit-Linux how code gets into the kernel

Release 4.11 ipc/sem.c

Directory: ipc
/*
 * 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 semaphore structure for each semaphore in the system. */

struct sem {
	
int	semval;		/* current value */
	/*
         * PID of the process that last modified the semaphore. For
         * Linux, specifically these are:
         *  - semop
         *  - semctl, via SETVAL and SETALL.
         *  - at task exit when performing undo adjustments (see exit_sem).
         */
	
int	sempid;
	
spinlock_t	lock;	/* spinlock for fine-grained semtimedop */
	
struct list_head pending_alter; /* pending single-sop operations */
					/* that alter the semaphore */
	
struct list_head pending_const; /* pending single-sop operations */
					/* that do not alter the semaphore*/
	
time_t	sem_otime;	/* candidate for sem_otime */
} 
____cacheline_aligned_in_smp;

/* 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.sem_base[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]); }

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Kirill Korotaev4384.31%133.33%
Pierre Peiffer713.73%133.33%
Linus Torvalds (pre-git)11.96%133.33%
Total51100.00%3100.00%

#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); }

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Kirill Korotaev1438.89%116.67%
Serge E. Hallyn1336.11%116.67%
Linus Torvalds (pre-git)411.11%233.33%
Nadia Derbey38.33%116.67%
Pierre Peiffer25.56%116.67%
Total36100.00%6100.00%

#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); }

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Kirill Korotaev1144.00%114.29%
Linus Torvalds (pre-git)1040.00%457.14%
Mike Waychison312.00%114.29%
Pierre Peiffer14.00%114.29%
Total25100.00%7100.00%

/** * 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->sem_base[q->sops[0].sem_num]; list_add_tail(&q->list, &curr->pending_alter); } INIT_LIST_HEAD(&sma->pending_alter); }

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Manfred Spraul83100.00%1100.00%
Total83100.00%1100.00%

/** * 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->sem_base + i; list_splice_init(&sem->pending_alter, &sma->pending_alter); } }

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Manfred Spraul55100.00%1100.00%
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static void sem_rcu_free(struct rcu_head *head) { struct ipc_rcu *p = container_of(head, struct ipc_rcu, rcu); struct sem_array *sma = ipc_rcu_to_struct(p); security_sem_free(sma); ipc_rcu_free(head); }

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Davidlohr Bueso A46100.00%1100.00%
Total46100.00%1100.00%

/* * 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->sem_base + i; spin_lock(&sem->lock); spin_unlock(&sem->lock); } }

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Manfred Spraul84100.00%5100.00%
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/* * 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--; } }

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Manfred Spraul50100.00%2100.00%
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#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->sem_base + 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; } }

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Manfred Spraul7245.86%342.86%
Rik Van Riel6943.95%228.57%
Nadia Derbey138.28%114.29%
Pierre Peiffer31.91%114.29%
Total157100.00%7100.00%


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->sem_base + locknum; spin_unlock(&sem->lock); } }

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Rik Van Riel5079.37%233.33%
Manfred Spraul1117.46%233.33%
Nadia Derbey11.59%116.67%
Davidlohr Bueso A11.59%116.67%
Total63100.00%6100.00%

/* * 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); }

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Nadia Derbey3052.63%233.33%
Davidlohr Bueso A1628.07%233.33%
Pierre Peiffer1017.54%116.67%
Rik Van Riel11.75%116.67%
Total57100.00%6100.00%


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); }

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Davidlohr Bueso A4375.44%125.00%
Nadia Derbey1221.05%250.00%
Pierre Peiffer23.51%125.00%
Total57100.00%4100.00%


static inline void sem_lock_and_putref(struct sem_array *sma) { sem_lock(sma, NULL, -1); ipc_rcu_putref(sma, sem_rcu_free); }

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Pierre Peiffer2172.41%125.00%
Rik Van Riel620.69%125.00%
Fabian Frederick13.45%125.00%
Davidlohr Bueso A13.45%125.00%
Total29100.00%4100.00%


static inline void sem_rmid(struct ipc_namespace *ns, struct sem_array *s) { ipc_rmid(&sem_ids(ns), &s->sem_perm); }

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Nadia Derbey31100.00%1100.00%
Total31100.00%1100.00%

/** * 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 id; int retval; struct sem_array *sma; int size; 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; size = sizeof(*sma) + nsems * sizeof(struct sem); sma = ipc_rcu_alloc(size); if (!sma) return -ENOMEM; memset(sma, 0, size); sma->sem_perm.mode = (semflg & S_IRWXUGO); sma->sem_perm.key = key; sma->sem_perm.security = NULL; retval = security_sem_alloc(sma); if (retval) { ipc_rcu_putref(sma, ipc_rcu_free); return retval; } sma->sem_base = (struct sem *) &sma[1]; for (i = 0; i < nsems; i++) { INIT_LIST_HEAD(&sma->sem_base[i].pending_alter); INIT_LIST_HEAD(&sma->sem_base[i].pending_const); spin_lock_init(&sma->sem_base[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(); id = ipc_addid(&sem_ids(ns), &sma->sem_perm, ns->sc_semmni); if (id < 0) { ipc_rcu_putref(sma, sem_rcu_free); return id; } ns->used_sems += nsems; sem_unlock(sma, -1); rcu_read_unlock(); return sma->sem_perm.id; }

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Manfred Spraul11933.71%830.77%
Linus Torvalds (pre-git)11733.14%623.08%
Nadia Derbey308.50%27.69%
Stephen D. Smalley267.37%13.85%
Greg Kroah-Hartman257.08%311.54%
Rik Van Riel185.10%13.85%
Kirill Korotaev92.55%13.85%
Linus Torvalds30.85%13.85%
Andi Kleen20.57%13.85%
Andrew Morton20.57%13.85%
Davidlohr Bueso A20.57%13.85%
Total353100.00%26100.00%

/* * 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); }

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Nadia Derbey40100.00%2100.00%
Total40100.00%2100.00%

/* * 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; }

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Nadia Derbey53100.00%2100.00%
Total53100.00%2100.00%

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->sem_base + 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->sem_base[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->sem_base[sop->sem_num].semval -= sem_op; if (sop->sem_flg & SEM_UNDO) un->semadj[sop->sem_num] += sem_op; sop--; } return result; }

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Linus Torvalds (pre-git)15547.99%440.00%
Andrew Morton5817.96%110.00%
Manfred Spraul4614.24%220.00%
Petr Mladek3510.84%110.00%
Linus Torvalds288.67%110.00%
Davidlohr Bueso A10.31%110.00%
Total323100.00%10100.00%


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->sem_base + 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->sem_base + 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; }

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PersonTokensPropCommitsCommitProp
Davidlohr Bueso A307100.00%1100.00%
Total307100.00%1100.00%


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

PersonTokensPropCommitsCommitProp
Nicholas Piggin2051.28%133.33%
Davidlohr Bueso A1230.77%133.33%
Manfred Spraul717.95%133.33%
Total39100.00%3100.00%


static void unlink_queue(struct sem_array *sma, struct sem_queue *q) { list_del(&q->list); if (q->nsops > 1) sma->complex_count--; }

Contributors

PersonTokensPropCommitsCommitProp
Manfred Spraul3697.30%150.00%
Rik Van Riel12.70%150.00%
Total37100.00%2100.00%

/** 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

PersonTokensPropCommitsCommitProp
Manfred Spraul4797.92%266.67%
Davidlohr Bueso A12.08%133.33%
Total48100.00%3100.00%

/** * 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->sem_base[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

PersonTokensPropCommitsCommitProp
Manfred Spraul10585.37%360.00%
Davidlohr Bueso A1814.63%240.00%
Total123100.00%5100.00%

/** * 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->sem_base[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->sem_base[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) semop_completed |= wake_const_ops(sma, -1, wake_q); return semop_completed; }

Contributors

PersonTokensPropCommitsCommitProp
Manfred Spraul16597.06%266.67%
Davidlohr Bueso A52.94%133.33%
Total170100.00%3100.00%

/** * update_queue - look for tasks that can be completed. * @sma: semaphore array. * @semnum: semaphore that was modified. * @wake_q: lockless wake-queue head. * * update_queue must be called after a semaphore in a semaphore array * was modified. If multiple semaphores were modified, update_queue 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 internally checks if const operations can now succeed. * * The function return 1 if at least one semop was completed successfully. */
static int update_queue(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_alter; else pending_list = &sma->sem_base[semnum].pending_alter; again: list_for_each_entry_safe(q, tmp, pending_list, list) { int error, restart; /* If we are scanning the single sop, per-semaphore list of * one semaphore and that semaphore is 0, then it is not * necessary to scan further: simple increments * that affect only one entry succeed immediately and cannot * be in the per semaphore pending queue, and decrements * cannot be successful if the value is already 0. */ if (semnum != -1 && sma->sem_base[semnum].semval == 0) break; error = perform_atomic_semop(sma, q); /* Does q->sleeper still need to sleep? */ if (error > 0) continue; unlink_queue(sma, q); if (error) { restart = 0; } else { semop_completed = 1; do_smart_wakeup_zero(sma, q->sops, q->nsops, wake_q); restart = check_restart(sma, q); } wake_up_sem_queue_prepare(q, error, wake_q); if (restart) goto again; } return semop_completed; }

Contributors

PersonTokensPropCommitsCommitProp
Manfred Spraul12164.71%947.37%
Linus Torvalds (pre-git)3116.58%421.05%
Davidlohr Bueso A179.09%210.53%
Nicholas Piggin147.49%210.53%
Andrew Morton42.14%210.53%
Total187100.00%19100.00%

/** * set_semotime - set sem_otime * @sma: semaphore array * @sops: operations that modified the array, may be NULL * * sem_otime is replicated to avoid cache line trashing. * This function sets one instance to the current time. */
static void set_semotime(struct sem_array *sma, struct sembuf *sops) {