/* * 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> * 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_semncnt() and * count_semzcnt() * - 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(), * wake_up_sem_queue_do()) * - 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). * - The synchronizations between wake-ups due to a timeout/signal and a * wake-up due to a completed semaphore operation is achieved by using an * intermediate state (IN_WAKEUP). * - 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 <asm/uaccess.h>#include "util.h" #define sem_ids(ns) ((ns)->ids[IPC_SEM_IDS]) #define sem_unlock(sma) ipc_unlock(&(sma)->sem_perm)#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_FSstatic 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 */ /* * linked list protection: * sem_undo.id_next, * sem_array.sem_pending{,last}, * sem_array.sem_undo: sem_lock() for read/write * sem_undo.proc_next: only "current" is allowed to read/write that field. * */ #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]);} #ifdef CONFIG_IPC_NSvoid sem_exit_ns(struct ipc_namespace *ns){ free_ipcs(ns, &sem_ids(ns), freeary); idr_destroy(&ns->ids[IPC_SEM_IDS].ipcs_idr);}#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);} /* * sem_lock_(check_) routines are called in the paths where the rw_mutex * is not held. */static inline struct sem_array *sem_lock(struct ipc_namespace *ns, int id){ struct kern_ipc_perm *ipcp = ipc_lock(&sem_ids(ns), id); if (IS_ERR(ipcp)) return (struct sem_array *)ipcp; return container_of(ipcp, struct sem_array, sem_perm);} static inline struct sem_array *sem_lock_check(struct ipc_namespace *ns, int id){ struct kern_ipc_perm *ipcp = ipc_lock_check(&sem_ids(ns), id); if (IS_ERR(ipcp)) return (struct sem_array *)ipcp; return container_of(ipcp, struct sem_array, sem_perm);} static inline void sem_lock_and_putref(struct sem_array *sma){ ipc_lock_by_ptr(&sma->sem_perm); ipc_rcu_putref(sma);} static inline void sem_getref_and_unlock(struct sem_array *sma){ ipc_rcu_getref(sma); ipc_unlock(&(sma)->sem_perm);} static inline void sem_putref(struct sem_array *sma){ ipc_lock_by_ptr(&sma->sem_perm); ipc_rcu_putref(sma); ipc_unlock(&(sma)->sem_perm);} static inline void sem_rmid(struct ipc_namespace *ns, struct sem_array *s){ ipc_rmid(&sem_ids(ns), &s->sem_perm);} /* * Lockless wakeup algorithm: * Without the check/retry algorithm a lockless wakeup is possible: * - queue.status is initialized to -EINTR before blocking. * - wakeup is performed by * * unlinking the queue entry from sma->sem_pending * * setting queue.status to IN_WAKEUP * This is the notification for the blocked thread that a * result value is imminent. * * call wake_up_process * * set queue.status to the final value. * - the previously blocked thread checks queue.status: * * if it's IN_WAKEUP, then it must wait until the value changes * * if it's not -EINTR, then the operation was completed by * update_queue. semtimedop can return queue.status without * performing any operation on the sem array. * * otherwise it must acquire the spinlock and check what's up. * * The two-stage algorithm is necessary to protect against the following * races: * - if queue.status is set after wake_up_process, then the woken up idle * thread could race forward and try (and fail) to acquire sma->lock * before update_queue had a chance to set queue.status * - if queue.status is written before wake_up_process and if the * blocked process is woken up by a signal between writing * queue.status and the wake_up_process, then the woken up * process could return from semtimedop and die by calling * sys_exit before wake_up_process is called. Then wake_up_process * will oops, because the task structure is already invalid. * (yes, this happened on s390 with sysv msg). * */#define IN_WAKEUP 1 /** * newary - Create a new semaphore set * @ns: namespace * @params: ptr to the structure that contains key, semflg and nsems * * Called with sem_ids.rw_mutex 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); return retval; } id = ipc_addid(&sem_ids(ns), &sma->sem_perm, ns->sc_semmni); if (id < 0) { security_sem_free(sma); ipc_rcu_putref(sma); return id; } ns->used_sems += nsems; sma->sem_base = (struct sem *) &sma[1]; for (i = 0; i < nsems; i++) INIT_LIST_HEAD(&sma->sem_base[i].sem_pending); sma->complex_count = 0; INIT_LIST_HEAD(&sma->sem_pending); INIT_LIST_HEAD(&sma->list_id); sma->sem_nsems = nsems; sma->sem_ctime = get_seconds(); sem_unlock(sma); return sma->sem_perm.id;} /* * Called with sem_ids.rw_mutex 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);} /* * Called with sem_ids.rw_mutex 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;} SYSCALL_DEFINE3(semget, key_t, key, int, nsems, int, semflg){ struct ipc_namespace *ns; struct ipc_ops sem_ops; struct ipc_params sem_params; ns = current->nsproxy->ipc_ns; if (nsems < 0 || nsems > ns->sc_semmsl) return -EINVAL; sem_ops.getnew = newary; sem_ops.associate = sem_security; sem_ops.more_checks = sem_more_checks; sem_params.key = key; sem_params.flg = semflg; sem_params.u.nsems = nsems; return ipcget(ns, &sem_ids(ns), &sem_ops, &sem_params);} /* * Determine whether a sequence of semaphore operations would succeed * all at once. Return 0 if yes, 1 if need to sleep, else return error code. */ static int try_atomic_semop (struct sem_array * sma, struct sembuf * sops, int nsops, struct sem_undo *un, int pid){ int result, sem_op; struct sembuf *sop; struct sem * curr; 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; } curr->semval = result; } sop--; while (sop >= sops) { sma->sem_base[sop->sem_num].sempid = pid; if (sop->sem_flg & SEM_UNDO) un->semadj[sop->sem_num] -= sop->sem_op; sop--; } return 0; out_of_range: result = -ERANGE; goto undo; would_block: if (sop->sem_flg & IPC_NOWAIT) result = -EAGAIN; else result = 1; undo: sop--; while (sop >= sops) { sma->sem_base[sop->sem_num].semval -= sop->sem_op; sop--; } return result;} /** wake_up_sem_queue_prepare(q, error): Prepare wake-up * @q: queue entry that must be signaled * @error: Error value for the signal * * Prepare the wake-up of the queue entry q. */static void wake_up_sem_queue_prepare(struct list_head *pt, struct sem_queue *q, int error){ if (list_empty(pt)) { /* * Hold preempt off so that we don't get preempted and have the * wakee busy-wait until we're scheduled back on. */ preempt_disable(); } q->status = IN_WAKEUP; q->pid = error; list_add_tail(&q->simple_list, pt);} /** * wake_up_sem_queue_do(pt) - do the actual wake-up * @pt: list of tasks to be woken up * * Do the actual wake-up. * The function is called without any locks held, thus the semaphore array * could be destroyed already and the tasks can disappear as soon as the * status is set to the actual return code. */static void wake_up_sem_queue_do(struct list_head *pt){ struct sem_queue *q, *t; int did_something; did_something = !list_empty(pt); list_for_each_entry_safe(q, t, pt, simple_list) { wake_up_process(q->sleeper); /* q can disappear immediately after writing q->status. */ smp_wmb(); q->status = q->pid; } if (did_something) preempt_enable();} static void unlink_queue(struct sem_array *sma, struct sem_queue *q){ list_del(&q->list); if (q->nsops == 1) list_del(&q->simple_list); else sma->complex_count--;} /** 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 * was completed. */static int check_restart(struct sem_array *sma, struct sem_queue *q){ struct sem *curr; struct sem_queue *h; /* if the operation didn't modify the array, then no restart */ if (q->alter == 0) return 0; /* pending complex operations are too difficult to analyse */ if (sma->complex_count) return 1; /* we were a sleeping complex operation. Too difficult */ if (q->nsops > 1) return 1; curr = sma->sem_base + q->sops[0].sem_num; /* No-one waits on this queue */ if (list_empty(&curr->sem_pending)) return 0; /* the new semaphore value */ if (curr->semval) { /* It is impossible that someone waits for the new value: * - q is a previously sleeping simple operation thatLines 1–500 of 1641. Load more
/* * 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> * 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_semncnt() and * count_semzcnt() * - 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(), * wake_up_sem_queue_do()) * - 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). * - The synchronizations between wake-ups due to a timeout/signal and a * wake-up due to a completed semaphore operation is achieved by using an * intermediate state (IN_WAKEUP). * - 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 <asm/uaccess.h> #include "util.h" #define sem_ids(ns) ((ns)->ids[IPC_SEM_IDS]) #define sem_unlock(sma) ipc_unlock(&(sma)->sem_perm) #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 */ /* * linked list protection: * sem_undo.id_next, * sem_array.sem_pending{,last}, * sem_array.sem_undo: sem_lock() for read/write * sem_undo.proc_next: only "current" is allowed to read/write that field. * */ #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]); } #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); } #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); } /* * sem_lock_(check_) routines are called in the paths where the rw_mutex * is not held. */ static inline struct sem_array *sem_lock(struct ipc_namespace *ns, int id) { struct kern_ipc_perm *ipcp = ipc_lock(&sem_ids(ns), id); if (IS_ERR(ipcp)) return (struct sem_array *)ipcp; return container_of(ipcp, struct sem_array, sem_perm); } static inline struct sem_array *sem_lock_check(struct ipc_namespace *ns, int id) { struct kern_ipc_perm *ipcp = ipc_lock_check(&sem_ids(ns), id); if (IS_ERR(ipcp)) return (struct sem_array *)ipcp; return container_of(ipcp, struct sem_array, sem_perm); } static inline void sem_lock_and_putref(struct sem_array *sma) { ipc_lock_by_ptr(&sma->sem_perm); ipc_rcu_putref(sma); } static inline void sem_getref_and_unlock(struct sem_array *sma) { ipc_rcu_getref(sma); ipc_unlock(&(sma)->sem_perm); } static inline void sem_putref(struct sem_array *sma) { ipc_lock_by_ptr(&sma->sem_perm); ipc_rcu_putref(sma); ipc_unlock(&(sma)->sem_perm); } static inline void sem_rmid(struct ipc_namespace *ns, struct sem_array *s) { ipc_rmid(&sem_ids(ns), &s->sem_perm); } /* * Lockless wakeup algorithm: * Without the check/retry algorithm a lockless wakeup is possible: * - queue.status is initialized to -EINTR before blocking. * - wakeup is performed by * * unlinking the queue entry from sma->sem_pending * * setting queue.status to IN_WAKEUP * This is the notification for the blocked thread that a * result value is imminent. * * call wake_up_process * * set queue.status to the final value. * - the previously blocked thread checks queue.status: * * if it's IN_WAKEUP, then it must wait until the value changes * * if it's not -EINTR, then the operation was completed by * update_queue. semtimedop can return queue.status without * performing any operation on the sem array. * * otherwise it must acquire the spinlock and check what's up. * * The two-stage algorithm is necessary to protect against the following * races: * - if queue.status is set after wake_up_process, then the woken up idle * thread could race forward and try (and fail) to acquire sma->lock * before update_queue had a chance to set queue.status * - if queue.status is written before wake_up_process and if the * blocked process is woken up by a signal between writing * queue.status and the wake_up_process, then the woken up * process could return from semtimedop and die by calling * sys_exit before wake_up_process is called. Then wake_up_process * will oops, because the task structure is already invalid. * (yes, this happened on s390 with sysv msg). * */ #define IN_WAKEUP 1 /** * newary - Create a new semaphore set * @ns: namespace * @params: ptr to the structure that contains key, semflg and nsems * * Called with sem_ids.rw_mutex 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); return retval; } id = ipc_addid(&sem_ids(ns), &sma->sem_perm, ns->sc_semmni); if (id < 0) { security_sem_free(sma); ipc_rcu_putref(sma); return id; } ns->used_sems += nsems; sma->sem_base = (struct sem *) &sma[1]; for (i = 0; i < nsems; i++) INIT_LIST_HEAD(&sma->sem_base[i].sem_pending); sma->complex_count = 0; INIT_LIST_HEAD(&sma->sem_pending); INIT_LIST_HEAD(&sma->list_id); sma->sem_nsems = nsems; sma->sem_ctime = get_seconds(); sem_unlock(sma); return sma->sem_perm.id; } /* * Called with sem_ids.rw_mutex 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); } /* * Called with sem_ids.rw_mutex 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; } SYSCALL_DEFINE3(semget, key_t, key, int, nsems, int, semflg) { struct ipc_namespace *ns; struct ipc_ops sem_ops; struct ipc_params sem_params; ns = current->nsproxy->ipc_ns; if (nsems < 0 || nsems > ns->sc_semmsl) return -EINVAL; sem_ops.getnew = newary; sem_ops.associate = sem_security; sem_ops.more_checks = sem_more_checks; sem_params.key = key; sem_params.flg = semflg; sem_params.u.nsems = nsems; return ipcget(ns, &sem_ids(ns), &sem_ops, &sem_params); } /* * Determine whether a sequence of semaphore operations would succeed * all at once. Return 0 if yes, 1 if need to sleep, else return error code. */ static int try_atomic_semop (struct sem_array * sma, struct sembuf * sops, int nsops, struct sem_undo *un, int pid) { int result, sem_op; struct sembuf *sop; struct sem * curr; 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; } curr->semval = result; } sop--; while (sop >= sops) { sma->sem_base[sop->sem_num].sempid = pid; if (sop->sem_flg & SEM_UNDO) un->semadj[sop->sem_num] -= sop->sem_op; sop--; } return 0; out_of_range: result = -ERANGE; goto undo; would_block: if (sop->sem_flg & IPC_NOWAIT) result = -EAGAIN; else result = 1; undo: sop--; while (sop >= sops) { sma->sem_base[sop->sem_num].semval -= sop->sem_op; sop--; } return result; } /** wake_up_sem_queue_prepare(q, error): Prepare wake-up * @q: queue entry that must be signaled * @error: Error value for the signal * * Prepare the wake-up of the queue entry q. */ static void wake_up_sem_queue_prepare(struct list_head *pt, struct sem_queue *q, int error) { if (list_empty(pt)) { /* * Hold preempt off so that we don't get preempted and have the * wakee busy-wait until we're scheduled back on. */ preempt_disable(); } q->status = IN_WAKEUP; q->pid = error; list_add_tail(&q->simple_list, pt); } /** * wake_up_sem_queue_do(pt) - do the actual wake-up * @pt: list of tasks to be woken up * * Do the actual wake-up. * The function is called without any locks held, thus the semaphore array * could be destroyed already and the tasks can disappear as soon as the * status is set to the actual return code. */ static void wake_up_sem_queue_do(struct list_head *pt) { struct sem_queue *q, *t; int did_something; did_something = !list_empty(pt); list_for_each_entry_safe(q, t, pt, simple_list) { wake_up_process(q->sleeper); /* q can disappear immediately after writing q->status. */ smp_wmb(); q->status = q->pid; } if (did_something) preempt_enable(); } static void unlink_queue(struct sem_array *sma, struct sem_queue *q) { list_del(&q->list); if (q->nsops == 1) list_del(&q->simple_list); else sma->complex_count--; } /** 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 * was completed. */ static int check_restart(struct sem_array *sma, struct sem_queue *q) { struct sem *curr; struct sem_queue *h; /* if the operation didn't modify the array, then no restart */ if (q->alter == 0) return 0; /* pending complex operations are too difficult to analyse */ if (sma->complex_count) return 1; /* we were a sleeping complex operation. Too difficult */ if (q->nsops > 1) return 1; curr = sma->sem_base + q->sops[0].sem_num; /* No-one waits on this queue */ if (list_empty(&curr->sem_pending)) return 0; /* the new semaphore value */ if (curr->semval) { /* It is impossible that someone waits for the new value: * - q is a previously sleeping simple operation that