diff options
| -rw-r--r-- | include/linux/sem.h | 12 | ||||
| -rw-r--r-- | ipc/sem.c | 92 |
2 files changed, 40 insertions, 64 deletions
diff --git a/include/linux/sem.h b/include/linux/sem.h index 87756ef..d425993 100644 --- a/include/linux/sem.h +++ b/include/linux/sem.h @@ -93,21 +93,19 @@ struct sem_array { time_t sem_otime; /* last semop time */ time_t sem_ctime; /* last change time */ struct sem *sem_base; /* ptr to first semaphore in array */ - struct sem_queue *sem_pending; /* pending operations to be processed */ - struct sem_queue **sem_pending_last; /* last pending operation */ + struct list_head sem_pending; /* pending operations to be processed */ struct list_head list_id; /* undo requests on this array */ unsigned long sem_nsems; /* no. of semaphores in array */ }; /* One queue for each sleeping process in the system. */ struct sem_queue { - struct sem_queue * next; /* next entry in the queue */ - struct sem_queue ** prev; /* previous entry in the queue, *(q->prev) == q */ - struct task_struct* sleeper; /* this process */ - struct sem_undo * undo; /* undo structure */ + 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 *sops; /* array of pending operations */ int nsops; /* number of operations */ int alter; /* does the operation alter the array? */ }; @@ -272,8 +272,7 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params) ns->used_sems += nsems; sma->sem_base = (struct sem *) &sma[1]; - /* sma->sem_pending = NULL; */ - sma->sem_pending_last = &sma->sem_pending; + INIT_LIST_HEAD(&sma->sem_pending); INIT_LIST_HEAD(&sma->list_id); sma->sem_nsems = nsems; sma->sem_ctime = get_seconds(); @@ -331,38 +330,6 @@ asmlinkage long sys_semget(key_t key, int nsems, int semflg) return ipcget(ns, &sem_ids(ns), &sem_ops, &sem_params); } -/* 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. @@ -438,16 +405,15 @@ static void update_queue (struct sem_array * sma) int error; struct sem_queue * q; - q = sma->sem_pending; - while(q) { + q = list_entry(sma->sem_pending.next, struct sem_queue, list); + while (&q->list != &sma->sem_pending) { 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 @@ -458,11 +424,26 @@ static void update_queue (struct sem_array * sma) * for semaphore values to become 0. * - if the operation didn't modify the array, * then just continue. + * The order of list_del() and reading ->next + * is crucial: In the former case, the list_del() + * must be done first [because we might be the + * first entry in ->sem_pending], in the latter + * case the list_del() must be done last + * [because the list is invalid after the list_del()] */ - if (q->alter) - n = sma->sem_pending; - else - n = q->next; + if (q->alter) { + list_del(&q->list); + n = list_entry(sma->sem_pending.next, + struct sem_queue, list); + } else { + n = list_entry(q->list.next, struct sem_queue, + list); + list_del(&q->list); + } + + /* wake up the waiting thread */ + q->status = IN_WAKEUP; + wake_up_process(q->sleeper); /* hands-off: q will disappear immediately after * writing q->status. @@ -471,7 +452,7 @@ static void update_queue (struct sem_array * sma) q->status = error; q = n; } else { - q = q->next; + q = list_entry(q->list.next, struct sem_queue, list); } } } @@ -491,7 +472,7 @@ static int count_semncnt (struct sem_array * sma, ushort semnum) struct sem_queue * q; semncnt = 0; - for (q = sma->sem_pending; q; q = q->next) { + list_for_each_entry(q, &sma->sem_pending, list) { struct sembuf * sops = q->sops; int nsops = q->nsops; int i; @@ -503,13 +484,14 @@ static int count_semncnt (struct sem_array * sma, ushort semnum) } 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) { + list_for_each_entry(q, &sma->sem_pending, list) { struct sembuf * sops = q->sops; int nsops = q->nsops; int i; @@ -529,7 +511,7 @@ static int count_semzcnt (struct sem_array * sma, ushort semnum) static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp) { struct sem_undo *un; - struct sem_queue *q; + struct sem_queue *q, *t; struct sem_array *sma = container_of(ipcp, struct sem_array, sem_perm); /* Invalidate the existing undo structures for this semaphore set. @@ -541,17 +523,14 @@ static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp) 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; + + list_for_each_entry_safe(q, t, &sma->sem_pending, list) { + list_del(&q->list); + 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 IDR */ @@ -1166,9 +1145,9 @@ asmlinkage long sys_semtimedop(int semid, struct sembuf __user *tsops, queue.pid = task_tgid_vnr(current); queue.alter = alter; if (alter) - append_to_queue(sma ,&queue); + list_add_tail(&queue.list, &sma->sem_pending); else - prepend_to_queue(sma ,&queue); + list_add(&queue.list, &sma->sem_pending); queue.status = -EINTR; queue.sleeper = current; @@ -1194,7 +1173,6 @@ asmlinkage long sys_semtimedop(int semid, struct sembuf __user *tsops, sma = sem_lock(ns, semid); if (IS_ERR(sma)) { - BUG_ON(queue.prev != NULL); error = -EIDRM; goto out_free; } @@ -1212,7 +1190,7 @@ asmlinkage long sys_semtimedop(int semid, struct sembuf __user *tsops, */ if (timeout && jiffies_left == 0) error = -EAGAIN; - remove_from_queue(sma,&queue); + list_del(&queue.list); goto out_unlock_free; out_unlock_free: |
