/* * linux/ipc/sem.c * Copyright (C) 1992 Krishna Balasubramanian * Copyright (C) 1995 Eric Schenk, Bruno Haible * * IMPLEMENTATION NOTES ON CODE REWRITE (Eric Schenk, January 1995): * This code underwent a massive rewrite in order to solve some problems * with the original code. In particular the original code failed to * wake up processes that were waiting for semval to go to 0 if the * value went to 0 and was then incremented rapidly enough. In solving * this problem I have also modified the implementation so that it * processes pending operations in a FIFO manner, thus give a guarantee * that processes waiting for a lock on the semaphore won't starve * unless another locking process fails to unlock. * In addition the following two changes in behavior have been introduced: * - The original implementation of semop returned the value * last semaphore element examined on success. This does not * match the manual page specifications, and effectively * allows the user to read the semaphore even if they do not * have read permissions. The implementation now returns 0 * on success as stated in the manual page. * - There is some confusion over whether the set of undo adjustments * to be performed at exit should be done in an atomic manner. * That is, if we are attempting to decrement the semval should we queue * up and wait until we can do so legally? * The original implementation attempted to do this. * The current implementation does not do so. This is because I don't * think it is the right thing (TM) to do, and because I couldn't * see a clean way to get the old behavior with the new design. * The POSIX standard and SVID should be consulted to determine * what behavior is mandated. * * Further notes on refinement (Christoph Rohland, December 1998): * - The POSIX standard says, that the undo adjustments simply should * redo. So the current implementation is o.K. * - The previous code had two flaws: * 1) It actively gave the semaphore to the next waiting process * sleeping on the semaphore. Since this process did not have the * cpu this led to many unnecessary context switches and bad * performance. Now we only check which process should be able to * get the semaphore and if this process wants to reduce some * semaphore value we simply wake it up without doing the * operation. So it has to try to get it later. Thus e.g. the * running process may reacquire the semaphore during the current * time slice. If it only waits for zero or increases the semaphore, * we do the operation in advance and wake it up. * 2) It did not wake up all zero waiting processes. We try to do * better but only get the semops right which only wait for zero or * increase. If there are decrement operations in the operations * array we do the same as before. * * With the incarnation of O(1) scheduler, it becomes unnecessary to perform * check/retry algorithm for waking up blocked processes as the new scheduler * is better at handling thread switch than the old one. * * /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 <alan@redhat.com> * Lockless wakeup * (c) 2003 Manfred Spraul <manfred@colorfullife.com> */ #include <linux/config.h> #include <linux/slab.h> #include <linux/spinlock.h> #include <linux/init.h> #include <linux/proc_fs.h> #include <linux/time.h> #include <linux/smp_lock.h> #include <linux/security.h> #include <linux/syscalls.h> #include <linux/audit.h> #include <linux/capability.h> #include <linux/seq_file.h> #include <linux/mutex.h> #include <asm/uaccess.h> #include "util.h" #define sem_lock(id) ((struct sem_array*)ipc_lock(&sem_ids,id)) #define sem_unlock(sma) ipc_unlock(&(sma)->sem_perm) #define sem_rmid(id) ((struct sem_array*)ipc_rmid(&sem_ids,id)) #define sem_checkid(sma, semid) \ ipc_checkid(&sem_ids,&sma->sem_perm,semid) #define sem_buildid(id, seq) \ ipc_buildid(&sem_ids, id, seq) static struct ipc_ids sem_ids; static int newary (key_t, int, int); static void freeary (struct sem_array *sma, int id); #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. * */ int sem_ctls[4] = {SEMMSL, SEMMNS, SEMOPM, SEMMNI}; #define sc_semmsl (sem_ctls[0]) #define sc_semmns (sem_ctls[1]) #define sc_semopm (sem_ctls[2]) #define sc_semmni (sem_ctls[3]) static int used_sems; void __init sem_init (void) { used_sems = 0; ipc_init_ids(&sem_ids,sc_semmni); ipc_init_proc_interface("sysvipc/sem", " key semid perms nsems uid gid cuid cgid otime ctime\n", &sem_ids, sysvipc_sem_proc_show); } /* * 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 static int newary (key_t key, int nsems, int semflg) { int id; int retval; struct sem_array *sma; int size; if (!nsems) return -EINVAL; if (used_sems + nsems > 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, &sma->sem_perm, sc_semmni); if(id == -1) { security_sem_free(sma); ipc_rcu_putref(sma); return -ENOSPC; } used_sems += nsems; sma->sem_id = sem_buildid(id, sma->sem_perm.seq); sma->sem_base = (struct sem *) &sma[1]; /* sma->sem_pending = NULL; */ sma->sem_pending_last = &sma->sem_pending; /* sma->undo = NULL; */ sma->sem_nsems = nsems; sma->sem_ctime = get_seconds(); sem_unlock(sma); return sma->sem_id; } asmlinkage long sys_semget (key_t key, int nsems, int semflg) { int id, err = -EINVAL; struct sem_array *sma; if (nsems < 0 || nsems > sc_semmsl) return -EINVAL; mutex_lock(&sem_ids.mutex); if (key == IPC_PRIVATE) { err = newary(key, nsems, semflg); } else if ((id = ipc_findkey(&sem_ids, key)) == -1) { /* key not used */ if (!(semflg & IPC_CREAT)) err = -ENOENT; else err = newary(key, nsems, semflg); } else if (semflg & IPC_CREAT && semflg & IPC_EXCL) { err = -EEXIST; } else { sma = sem_lock(id); BUG_ON(sma==NULL); if (nsems > sma->sem_nsems) err = -EINVAL; else if (ipcperms(&sma->sem_perm, semflg)) err = -EACCES; else { int semid = sem_buildid(id, sma->sem_perm.seq); err = security_sem_associate(sma, semflg); if (!err) err = semid; } sem_unlock(sma); } mutex_unlock(&sem_ids.mutex); return err; } /* Manage the doubly linked list sma->sem_pending as a FIFO: * insert new queue elements at the tail sma->sem_pending_last. */ static inline void append_to_queue (struct sem_array * sma, struct sem_queue * q) { *(q->prev = sma->sem_pending_last) = q; *(sma->sem_pending_last = &q->next) = NULL; } static inline void prepend_to_queue (struct sem_array * sma, struct sem_queue * q) { q->next = sma->sem_pending; *(q->prev = &sma->sem_pending) = q; if (q->next) q->next->prev = &q->next; else /* sma->sem_pending_last == &sma->sem_pending */ sma->sem_pending_last = &q->next; } static inline void remove_from_queue (struct sem_array * sma, struct sem_queue * q) { *(q->prev) = q->next; if (q->next) q->next->prev = q->prev; else /* sma->sem_pending_last == &q->next */ sma->sem_pending_last = q->prev; q->prev = NULL; /* mark as removed */ } /* * 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--; } sma->sem_otime = get_seconds(); 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; } /* Go through the pending queue for the indicated semaphore * looking for tasks that can be completed. */ static void update_queue (struct sem_array * sma) { int error; struct sem_queue * q; q = sma->sem_pending; while(q) { error = try_atomic_semop(sma, q->sops, q->nsops, q->undo, q->pid); /* Does q->sleeper still need to sleep? */ if (error <= 0) { struct sem_queue *n; remove_from_queue(sma,q); q->status = IN_WAKEUP; /* * Continue scanning. The next operation * that must be checked depends on the type of the * completed operation: * - if the operation modified the array, then * restart from the head of the queue and * check for threads that might be waiting * for semaphore values to become 0. * - if the operation didn't modify the array, * then just continue. */ if (q->alter) n = sma->sem_pending; else n = q->next; wake_up_process(q->sleeper); /* hands-off: q will disappear immediately after * writing q->status. */ smp_wmb(); q->status = error; q = n; } else { q = q->next; } } } /* The following counts are associated to each semaphore: * semncnt number of tasks waiting on semval being nonzero * semzcnt number of tasks waiting on semval being zero * This model assumes that a task waits on exactly one semaphore. * Since semaphore operations are to be performed atomically, tasks actually * wait on a whole sequence of semaphores simultaneously. * The counts we return here are a rough approximation, but still * warrant that semncnt+semzcnt>0 if the task is on the pending queue. */ static int count_semncnt (struct sem_array * sma, ushort semnum) { int semncnt; struct sem_queue * q; semncnt = 0; for (q = sma->sem_pending; q; q = q->next) { struct sembuf * sops = q->sops; int nsops = q->nsops; int i; for (i = 0; i < nsops; i++) if (sops[i].sem_num == semnum && (sops[i].sem_op < 0) && !(sops[i].sem_flg & IPC_NOWAIT)) semncnt++; } return semncnt; } static int count_semzcnt (struct sem_array * sma, ushort semnum) { int semzcnt; struct sem_queue * q; semzcnt = 0; for (q = sma->sem_pending; q; q = q->next) { struct sembuf * sops = q->sops; int nsops = q->nsops; int i; for (i = 0; i < nsops; i++) if (sops[i].sem_num == semnum && (sops[i].sem_op == 0) && !(sops[i].sem_flg & IPC_NOWAIT)) semzcnt++; } return semzcnt; } /* Free a semaphore set. freeary() is called with sem_ids.mutex locked and * the spinlock for this semaphore set hold. sem_ids.mutex remains locked * on exit. */ static void freeary (struct sem_array *sma, int id) { struct sem_undo *un; struct sem_queue *q; int size; /* Invalidate the existing undo structures for this semaphore set. * (They will be freed without any further action in exit_sem() * or during the next semop.) */ for (un = sma->undo; un; un = un->id_next) un->semid = -1; /* Wake up all pending processes and let them fail with EIDRM. */ q = sma->sem_pending; while(q) { struct sem_queue *n; /* lazy remove_from_queue: we are killing the whole queue */ q->prev = NULL; n = q->next; q->status = IN_WAKEUP; wake_up_process(q->sleeper); /* doesn't sleep */ smp_wmb(); q->status = -EIDRM; /* hands-off q */ q = n; } /* Remove the semaphore set from the ID array*/ sma = sem_rmid(id); sem_unlock(sma); used_sems -= sma->sem_nsems; size = sizeof (*sma) + sma->sem_nsems * sizeof (struct sem); security_sem_free(sma); ipc_rcu_putref(sma); } static unsigned long copy_semid_to_user(void __user *buf, struct semid64_ds *in, int version) { switch(version) { case IPC_64: return copy_to_user(buf, in, sizeof(*in)); case IPC_OLD: { struct semid_ds out; ipc64_perm_to_ipc_perm(&in->sem_perm, &out.sem_perm); out.sem_otime = in->sem_otime; out.sem_ctime = in->sem_ctime; out.sem_nsems = in->sem_nsems; return copy_to_user(buf, &out, sizeof(out)); } default: return -EINVAL; } } static int semctl_nolock(int semid, int semnum, int cmd, int version, union semun arg) { int err = -EINVAL; struct sem_array *sma; switch(cmd) { case IPC_INFO: case SEM_INFO: { struct seminfo seminfo; int max_id; err = security_sem_semctl(NULL, cmd); if (err) return err; memset(&seminfo,0,sizeof(seminfo)); seminfo.semmni = sc_semmni; seminfo.semmns = sc_semmns; seminfo.semmsl = sc_semmsl; seminfo.semopm = sc_semopm; seminfo.semvmx = SEMVMX; seminfo.semmnu = SEMMNU; seminfo.semmap = SEMMAP; seminfo.semume = SEMUME; mutex_lock(&sem_ids.mutex); if (cmd == SEM_INFO) { seminfo.semusz = sem_ids.in_use; seminfo.semaem = used_sems; } else { seminfo.semusz = SEMUSZ; seminfo.semaem = SEMAEM; } max_id = sem_ids.max_id; mutex_unlock(&sem_ids.mutex); if (copy_to_user (arg.__buf, &seminfo, sizeof(struct seminfo))) return -EFAULT; return (max_id < 0) ? 0: max_id; } case SEM_STAT: { struct semid64_ds tbuf; int id; if(semid >= sem_ids.entries->size) return -EINVAL; memset(&tbuf,0,sizeof(tbuf)); sma = sem_lock(semid); if(sma == NULL) return -EINVAL; err = -EACCES; if (ipcperms (&sma->sem_perm, S_IRUGO)) goto out_unlock; err = security_sem_semctl(sma, cmd); if (err) goto out_unlock; id = sem_buildid(semid, sma->sem_perm.seq); kernel_to_ipc64_perm(&sma->sem_perm, &tbuf.sem_perm); tbuf.sem_otime = sma->sem_otime; tbuf.sem_ctime = sma->sem_ctime; tbuf.sem_nsems = sma->sem_nsems; sem_unlock(sma); if (copy_semid_to_user (arg.buf, &tbuf, version)) return -EFAULT; return id; } default: return -EINVAL; } return err; out_unlock: sem_unlock(sma); return err; } static int semctl_main(int semid, int semnum, int cmd, int version, union semun arg) { struct sem_array *sma; struct sem* curr; int err; ushort fast_sem_io[SEMMSL_FAST]; ushort* sem_io = fast_sem_io; int nsems; sma = sem_lock(semid); if(sma==NULL) return -EINVAL; nsems = sma->sem_nsems; err=-EIDRM; if (sem_checkid(sma,semid)) goto out_unlock; err = -EACCES; if (ipcperms (&sma->sem_perm, (cmd==SETVAL||cmd==SETALL)?S_IWUGO:S_IRUGO)) goto out_unlock; err = security_sem_semctl(sma, cmd); if (err) goto out_unlock; err = -EACCES; switch (cmd) { case GETALL: { ushort __user *array = arg.array; int i; if(nsems > SEMMSL_FAST) { ipc_rcu_getref(sma); sem_unlock(sma); sem_io = ipc_alloc(sizeof(ushort)*nsems); if(sem_io == NULL) { ipc_lock_by_ptr(&sma->sem_perm); ipc_rcu_putref(sma); sem_unlock(sma); return -ENOMEM; } ipc_lock_by_ptr(&sma->sem_perm); ipc_rcu_putref(sma); if (sma->sem_perm.deleted) { sem_unlock(sma); err = -EIDRM; goto out_free; } } for (i = 0; i < sma->sem_nsems; i++) sem_io[i] = sma->sem_base[i].semval; sem_unlock(sma); err = 0; if(copy_to_user(array, sem_io, nsems*sizeof(ushort))) err = -EFAULT; goto out_free; } case SETALL: { int i; struct sem_undo *un; ipc_rcu_getref(sma); sem_unlock(sma); if(nsems > SEMMSL_FAST) { sem_io = ipc_alloc(sizeof(ushort)*nsems); if(sem_io == NULL) { ipc_lock_by_ptr(&sma->sem_perm); ipc_rcu_putref(sma); sem_unlock(sma); return -ENOMEM; } } if (copy_from_user (sem_io, arg.array, nsems*sizeof(ushort))) { ipc_lock_by_ptr(&sma->sem_perm); ipc_rcu_putref(sma); sem_unlock(sma); err = -EFAULT; goto out_free; } for (i = 0; i < nsems; i++) { if (sem_io[i] > SEMVMX) { ipc_lock_by_ptr(&sma->sem_perm); ipc_rcu_putref(sma); sem_unlock(sma); err = -ERANGE; goto out_free; } } ipc_lock_by_ptr(&sma->sem_perm); ipc_rcu_putref(sma); if (sma->sem_perm.deleted) { sem_unlock(sma); err = -EIDRM; goto out_free; } for (i = 0; i < nsems; i++) sma->sem_base[i].semval = sem_io[i]; for (un = sma->undo; un; un = un->id_next) for (i = 0; i < nsems; i++) un->semadj[i] = 0; sma->sem_ctime = get_seconds(); /* maybe some queued-up processes were waiting for this */ update_queue(sma); err = 0; goto out_unlock; } case IPC_STAT: { struct semid64_ds tbuf; memset(&tbuf,0,sizeof(tbuf)); kernel_to_ipc64_perm(&sma->sem_perm, &tbuf.sem_perm); tbuf.sem_otime = sma->sem_otime; tbuf.sem_ctime = sma->sem_ctime; tbuf.sem_nsems = sma->sem_nsems; sem_unlock(sma); if (copy_semid_to_user (arg.buf, &tbuf, version)) return -EFAULT; return 0; } /* GETVAL, GETPID, GETNCTN, GETZCNT, SETVAL: fall-through */ } err = -EINVAL; if(semnum < 0 || semnum >= nsems) goto out_unlock; curr = &sma->sem_base[semnum]; switch (cmd) { case GETVAL: err = curr->semval; goto out_unlock; case GETPID: err = curr->sempid; goto out_unlock; case GETNCNT: err = count_semncnt(sma,semnum); goto out_unlock; case GETZCNT: err = count_semzcnt(sma,semnum); goto out_unlock; case SETVAL: { int val = arg.val; struct sem_undo *un; err = -ERANGE; if (val > SEMVMX || val < 0) goto out_unlock; for (un = sma->undo; un; un = un->id_next) un->semadj[semnum] = 0; curr->semval = val; curr->sempid = current->tgid; sma->sem_ctime = get_seconds(); /* maybe some queued-up processes were waiting for this */ update_queue(sma); err = 0; goto out_unlock; } } out_unlock: sem_unlock(sma); out_free: if(sem_io != fast_sem_io) ipc_free(sem_io, sizeof(ushort)*nsems); return err; } struct sem_setbuf { uid_t uid; gid_t gid; mode_t mode; }; static inline unsigned long copy_semid_from_user(struct sem_setbuf *out, void __user *buf, int version) { switch(version) { case IPC_64: { struct semid64_ds tbuf; if(copy_from_user(&tbuf, buf, sizeof(tbuf))) return -EFAULT; out->uid = tbuf.sem_perm.uid; out->gid = tbuf.sem_perm.gid; out->mode = tbuf.sem_perm.mode; return 0; } case IPC_OLD: { struct semid_ds tbuf_old; if(copy_from_user(&tbuf_old, buf, sizeof(tbuf_old))) return -EFAULT; out->uid = tbuf_old.sem_perm.uid; out->gid = tbuf_old.sem_perm.gid; out->mode = tbuf_old.sem_perm.mode; return 0; } default: return -EINVAL; } } static int semctl_down(int semid, int semnum, int cmd, int version, union semun arg) { struct sem_array *sma; int err; struct sem_setbuf setbuf; struct kern_ipc_perm *ipcp; if(cmd == IPC_SET) { if(copy_semid_from_user (&setbuf, arg.buf, version)) return -EFAULT; } sma = sem_lock(semid); if(sma==NULL) return -EINVAL; if (sem_checkid(sma,semid)) { err=-EIDRM; goto out_unlock; } ipcp = &sma->sem_perm; if (current->euid != ipcp->cuid && current->euid != ipcp->uid && !capable(CAP_SYS_ADMIN)) { err=-EPERM; goto out_unlock; } err = security_sem_semctl(sma, cmd); if (err) goto out_unlock; switch(cmd){ case IPC_RMID: freeary(sma, semid); err = 0; break; case IPC_SET: if ((err = audit_ipc_perms(0, setbuf.uid, setbuf.gid, setbuf.mode, ipcp))) goto out_unlock; ipcp->uid = setbuf.uid; ipcp->gid = setbuf.gid; ipcp->mode = (ipcp->mode & ~S_IRWXUGO) | (setbuf.mode & S_IRWXUGO); sma->sem_ctime = get_seconds(); sem_unlock(sma); err = 0; break; default: sem_unlock(sma); err = -EINVAL; break; } return err; out_unlock: sem_unlock(sma); return err; } asmlinkage long sys_semctl (int semid, int semnum, int cmd, union semun arg) { int err = -EINVAL; int version; if (semid < 0) return -EINVAL; version = ipc_parse_version(&cmd); switch(cmd) { case IPC_INFO: case SEM_INFO: case SEM_STAT: err = semctl_nolock(semid,semnum,cmd,version,arg); return err; case GETALL: case GETVAL: case GETPID: case GETNCNT: case GETZCNT: case IPC_STAT: case SETVAL: case SETALL: err = semctl_main(semid,semnum,cmd,version,arg); return err; case IPC_RMID: case IPC_SET: mutex_lock(&sem_ids.mutex); err = semctl_down(semid,semnum,cmd,version,arg); mutex_unlock(&sem_ids.mutex); return err; default: return -EINVAL; } } static inline void lock_semundo(void) { struct sem_undo_list *undo_list; undo_list = current->sysvsem.undo_list; if (undo_list) spin_lock(&undo_list->lock); } /* This code has an interaction with copy_semundo(). * Consider; two tasks are sharing the undo_list. task1 * acquires the undo_list lock in lock_semundo(). If task2 now * exits before task1 releases the lock (by calling * unlock_semundo()), then task1 will never call spin_unlock(). * This leave the sem_undo_list in a locked state. If task1 now creats task3 * and once again shares the sem_undo_list, the sem_undo_list will still be * locked, and future SEM_UNDO operations will deadlock. This case is * dealt with in copy_semundo() by having it reinitialize the spin lock when * the refcnt goes from 1 to 2. */ static inline void unlock_semundo(void) { struct sem_undo_list *undo_list; undo_list = current->sysvsem.undo_list; if (undo_list) spin_unlock(&undo_list->lock); } /* If the task doesn't already have a undo_list, then allocate one * here. We guarantee there is only one thread using this undo list, * and current is THE ONE * * If this allocation and assignment succeeds, but later * portions of this code fail, there is no need to free the sem_undo_list. * Just let it stay associated with the task, and it'll be freed later * at exit time. * * This can block, so callers must hold no locks. */ static inline int get_undo_list(struct sem_undo_list **undo_listp) { struct sem_undo_list *undo_list; int size; undo_list = current->sysvsem.undo_list; if (!undo_list) { size = sizeof(struct sem_undo_list); undo_list = (struct sem_undo_list *) kmalloc(size, GFP_KERNEL); if (undo_list == NULL) return -ENOMEM; memset(undo_list, 0, size); spin_lock_init(&undo_list->lock); atomic_set(&undo_list->refcnt, 1); current->sysvsem.undo_list = undo_list; } *undo_listp = undo_list; return 0; } static struct sem_undo *lookup_undo(struct sem_undo_list *ulp, int semid) { struct sem_undo **last, *un; last = &ulp->proc_list; un = *last; while(un != NULL) { if(un->semid==semid) break; if(un->semid==-1) { *last=un->proc_next; kfree(un); } else { last=&un->proc_next; } un=*last; } return un; } static struct sem_undo *find_undo(int semid) { struct sem_array *sma; struct sem_undo_list *ulp; struct sem_undo *un, *new; int nsems; int error; error = get_undo_list(&ulp); if (error) return ERR_PTR(error); lock_semundo(); un = lookup_undo(ulp, semid); unlock_semundo(); if (likely(un!=NULL)) goto out; /* no undo structure around - allocate one. */ sma = sem_lock(semid); un = ERR_PTR(-EINVAL); if(sma==NULL) goto out; un = ERR_PTR(-EIDRM); if (sem_checkid(sma,semid)) { sem_unlock(sma); goto out; } nsems = sma->sem_nsems; ipc_rcu_getref(sma); sem_unlock(sma); new = (struct sem_undo *) kmalloc(sizeof(struct sem_undo) + sizeof(short)*nsems, GFP_KERNEL); if (!new) { ipc_lock_by_ptr(&sma->sem_perm); ipc_rcu_putref(sma); sem_unlock(sma); return ERR_PTR(-ENOMEM); } memset(new, 0, sizeof(struct sem_undo) + sizeof(short)*nsems); new->semadj = (short *) &new[1]; new->semid = semid; lock_semundo(); un = lookup_undo(ulp, semid); if (un) { unlock_semundo(); kfree(new); ipc_lock_by_ptr(&sma->sem_perm); ipc_rcu_putref(sma); sem_unlock(sma); goto out; } ipc_lock_by_ptr(&sma->sem_perm); ipc_rcu_putref(sma); if (sma->sem_perm.deleted) { sem_unlock(sma); unlock_semundo(); kfree(new); un = ERR_PTR(-EIDRM); goto out; } new->proc_next = ulp->proc_list; ulp->proc_list = new; new->id_next = sma->undo; sma->undo = new; sem_unlock(sma); un = new; unlock_semundo(); out: return un; } asmlinkage long sys_semtimedop(int semid, struct sembuf __user *tsops, unsigned nsops, const struct timespec __user *timeout) { int error = -EINVAL; struct sem_array *sma; struct sembuf fast_sops[SEMOPM_FAST]; struct sembuf* sops = fast_sops, *sop; struct sem_undo *un; int undos = 0, alter = 0, max; struct sem_queue queue; unsigned long jiffies_left = 0; if (nsops < 1 || semid < 0) return -EINVAL; if (nsops > sc_semopm) return -E2BIG; if(nsops > SEMOPM_FAST) { sops = kmalloc(sizeof(*sops)*nsops,GFP_KERNEL); if(sops==NULL) return -ENOMEM; } if (copy_from_user (sops, tsops, nsops * sizeof(*tsops))) { error=-EFAULT; goto out_free; } if (timeout) { struct timespec _timeout; if (copy_from_user(&_timeout, timeout, sizeof(*timeout))) { error = -EFAULT; goto out_free; } if (_timeout.tv_sec < 0 || _timeout.tv_nsec < 0 || _timeout.tv_nsec >= 1000000000L) { error = -EINVAL; goto out_free; } jiffies_left = timespec_to_jiffies(&_timeout); } max = 0; for (sop = sops; sop < sops + nsops; sop++) { if (sop->sem_num >= max) max = sop->sem_num; if (sop->sem_flg & SEM_UNDO) undos = 1; if (sop->sem_op != 0) alter = 1; } retry_undos: if (undos) { un = find_undo(semid); if (IS_ERR(un)) { error = PTR_ERR(un); goto out_free; } } else un = NULL; sma = sem_lock(semid); error=-EINVAL; if(sma==NULL) goto out_free; error = -EIDRM; if (sem_checkid(sma,semid)) goto out_unlock_free; /* * semid identifies are not unique - find_undo may have * allocated an undo structure, it was invalidated by an RMID * and now a new array with received the same id. Check and retry. */ if (un && un->semid == -1) { sem_unlock(sma); goto retry_undos; } error = -EFBIG; if (max >= sma->sem_nsems) goto out_unlock_free; error = -EACCES; if (ipcperms(&sma->sem_perm, alter ? S_IWUGO : S_IRUGO)) goto out_unlock_free; error = security_sem_semop(sma, sops, nsops, alter); if (error) goto out_unlock_free; error = try_atomic_semop (sma, sops, nsops, un, current->tgid); if (error <= 0) { if (alter && error == 0) update_queue (sma); goto out_unlock_free; } /* We need to sleep on this operation, so we put the current * task into the pending queue and go to sleep. */ queue.sma = sma; queue.sops = sops; queue.nsops = nsops; queue.undo = un; queue.pid = current->tgid; queue.id = semid; queue.alter = alter; if (alter) append_to_queue(sma ,&queue); else prepend_to_queue(sma ,&queue); queue.status = -EINTR; queue.sleeper = current; current->state = TASK_INTERRUPTIBLE; sem_unlock(sma); if (timeout) jiffies_left = schedule_timeout(jiffies_left); else schedule(); error = queue.status; while(unlikely(error == IN_WAKEUP)) { cpu_relax(); error = queue.status; } if (error != -EINTR) { /* fast path: update_queue already obtained all requested * resources */ goto out_free; } sma = sem_lock(semid); if(sma==NULL) { BUG_ON(queue.prev != NULL); error = -EIDRM; goto out_free; } /* * If queue.status != -EINTR we are woken up by another process */ error = queue.status; if (error != -EINTR) { goto out_unlock_free; } /* * If an interrupt occurred we have to clean up the queue */ if (timeout && jiffies_left == 0) error = -EAGAIN; remove_from_queue(sma,&queue); goto out_unlock_free; out_unlock_free: sem_unlock(sma); out_free: if(sops != fast_sops) kfree(sops); return error; } asmlinkage long sys_semop (int semid, struct sembuf __user *tsops, unsigned nsops) { return sys_semtimedop(semid, tsops, nsops, NULL); } /* If CLONE_SYSVSEM is set, establish sharing of SEM_UNDO state between * parent and child tasks. * * See the notes above unlock_semundo() regarding the spin_lock_init() * in this code. Initialize the undo_list->lock here instead of get_undo_list() * because of the reasoning in the comment above unlock_semundo. */ int copy_semundo(unsigned long clone_flags, struct task_struct *tsk) { struct sem_undo_list *undo_list; int error; if (clone_flags & CLONE_SYSVSEM) { error = get_undo_list(&undo_list); if (error) return error; atomic_inc(&undo_list->refcnt); tsk->sysvsem.undo_list = undo_list; } else tsk->sysvsem.undo_list = NULL; return 0; } /* * add semadj values to semaphores, free undo structures. * undo structures are not freed when semaphore arrays are destroyed * so some of them may be out of date. * IMPLEMENTATION NOTE: There is some confusion over whether the * set of adjustments that needs to be done should be done in an atomic * manner or not. That is, if we are attempting to decrement the semval * should we queue up and wait until we can do so legally? * The original implementation attempted to do this (queue and wait). * The current implementation does not do so. The POSIX standard * and SVID should be consulted to determine what behavior is mandated. */ void exit_sem(struct task_struct *tsk) { struct sem_undo_list *undo_list; struct sem_undo *u, **up; undo_list = tsk->sysvsem.undo_list; if (!undo_list) return; if (!atomic_dec_and_test(&undo_list->refcnt)) return; /* There's no need to hold the semundo list lock, as current * is the last task exiting for this undo list. */ for (up = &undo_list->proc_list; (u = *up); *up = u->proc_next, kfree(u)) { struct sem_array *sma; int nsems, i; struct sem_undo *un, **unp; int semid; semid = u->semid; if(semid == -1) continue; sma = sem_lock(semid); if (sma == NULL) continue; if (u->semid == -1) goto next_entry; BUG_ON(sem_checkid(sma,u->semid)); /* remove u from the sma->undo list */ for (unp = &sma->undo; (un = *unp); unp = &un->id_next) { if (u == un) goto found; } printk ("exit_sem undo list error id=%d\n", u->semid); goto next_entry; found: *unp = un->id_next; /* perform adjustments registered in u */ nsems = sma->sem_nsems; for (i = 0; i < nsems; i++) { struct sem * semaphore = &sma->sem_base[i]; if (u->semadj[i]) { semaphore->semval += u->semadj[i]; /* * Range checks of the new semaphore value, * not defined by sus: * - Some unices ignore the undo entirely * (e.g. HP UX 11i 11.22, Tru64 V5.1) * - some cap the value (e.g. FreeBSD caps * at 0, but doesn't enforce SEMVMX) * * Linux caps the semaphore value, both at 0 * and at SEMVMX. * * Manfred <manfred@colorfullife.com> */ if (semaphore->semval < 0) semaphore->semval = 0; if (semaphore->semval > SEMVMX) semaphore->semval = SEMVMX; semaphore->sempid = current->tgid; } } sma->sem_otime = get_seconds(); /* maybe some queued-up processes were waiting for this */ update_queue(sma); next_entry: sem_unlock(sma); } kfree(undo_list); } #ifdef CONFIG_PROC_FS static int sysvipc_sem_proc_show(struct seq_file *s, void *it) { struct sem_array *sma = it; return seq_printf(s, "%10d %10d %4o %10lu %5u %5u %5u %5u %10lu %10lu\n", sma->sem_perm.key, sma->sem_id, sma->sem_perm.mode, sma->sem_nsems, sma->sem_perm.uid, sma->sem_perm.gid, sma->sem_perm.cuid, sma->sem_perm.cgid, sma->sem_otime, sma->sem_ctime); } #endif