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 */
int alter; /* does *sops alter the array? */
};
/**
* perform_atomic_semop - Perform (if possible) a semaphore operation
* @sma: semaphore array
- * @sops: array with operations that should be checked
- * @nsops: number of operations
- * @un: undo array
- * @pid: pid that did the change
+ * @q: struct sem_queue that describes the operation
*
* Returns 0 if the operation was possible.
* Returns 1 if the operation is impossible, the caller must sleep.
* Negative values are error codes.
*/
-static int perform_atomic_semop(struct sem_array *sma, struct sembuf *sops,
- int nsops, struct sem_undo *un, int pid)
+static int perform_atomic_semop(struct sem_array *sma, struct sem_queue *q)
{
- int result, sem_op;
+ 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;
}
sop--;
+ pid = q->pid;
while (sop >= sops) {
sma->sem_base[sop->sem_num].sempid = pid;
sop--;
goto undo;
would_block:
+ q->blocking = sop;
+
if (sop->sem_flg & IPC_NOWAIT)
result = -EAGAIN;
else
q = container_of(walk, struct sem_queue, list);
walk = walk->next;
- error = perform_atomic_semop(sma, q->sops, q->nsops,
- q->undo, q->pid);
+ error = perform_atomic_semop(sma, q);
if (error <= 0) {
/* operation completed, remove from queue & wakeup */
if (semnum != -1 && sma->sem_base[semnum].semval == 0)
break;
- error = perform_atomic_semop(sma, q->sops, q->nsops,
- q->undo, q->pid);
+ error = perform_atomic_semop(sma, q);
/* Does q->sleeper still need to sleep? */
if (error > 0)
}
/*
- * check_qop: Test how often a queued operation sleeps on the semaphore semnum
+ * check_qop: Test if a queued operation sleeps on the semaphore semnum
*/
static int check_qop(struct sem_array *sma, int semnum, struct sem_queue *q,
bool count_zero)
{
- struct sembuf *sops = q->sops;
- int nsops = q->nsops;
- int i, semcnt;
+ struct sembuf *sop = q->blocking;
- semcnt = 0;
+ /*
+ * Linux always (since 0.99.10) reported a task as sleeping on all
+ * semaphores. This violates SUS, therefore it was changed to the
+ * standard compliant behavior.
+ * Give the administrators a chance to notice that an application
+ * might misbehave because it relies on the Linux behavior.
+ */
+ pr_info_once("semctl(GETNCNT/GETZCNT) is since 3.16 Single Unix Specification compliant.\n"
+ "The task %s (%d) triggered the difference, watch for misbehavior.\n",
+ current->comm, task_pid_nr(current));
- for (i = 0; i < nsops; i++) {
- if (sops[i].sem_num != semnum)
- continue;
- if (sops[i].sem_flg & IPC_NOWAIT)
- continue;
- if (count_zero && sops[i].sem_op == 0)
- semcnt++;
- if (!count_zero && sops[i].sem_op < 0)
- semcnt++;
- }
- return semcnt;
+ if (sop->sem_num != semnum)
+ return 0;
+
+ if (count_zero && sop->sem_op == 0)
+ return 1;
+ if (!count_zero && sop->sem_op < 0)
+ return 1;
+
+ return 0;
}
/* 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.
+ *
+ * Per definition, a task waits only on the semaphore of the first semop
+ * that cannot proceed, even if additional operation would block, too.
*/
static int count_semcnt(struct sem_array *sma, ushort semnum,
bool count_zero)
if (un && un->semid == -1)
goto out_unlock_free;
- error = perform_atomic_semop(sma, sops, nsops, un,
- task_tgid_vnr(current));
+ queue.sops = sops;
+ queue.nsops = nsops;
+ queue.undo = un;
+ queue.pid = task_tgid_vnr(current);
+ queue.alter = alter;
+
+ error = perform_atomic_semop(sma, &queue);
if (error == 0) {
/* If the operation was successful, then do
* the required updates.
* task into the pending queue and go to sleep.
*/
- queue.sops = sops;
- queue.nsops = nsops;
- queue.undo = un;
- queue.pid = task_tgid_vnr(current);
- queue.alter = alter;
-
if (nsops == 1) {
struct sem *curr;
curr = &sma->sem_base[sops->sem_num];
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