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-rw-r--r--ipc/sem.c46
1 files changed, 39 insertions, 7 deletions
diff --git a/ipc/sem.c b/ipc/sem.c
index 506c8491a8d..40a8f462a82 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -1256,6 +1256,33 @@ out:
return un;
}
+
+/**
+ * get_queue_result - Retrieve the result code from sem_queue
+ * @q: Pointer to queue structure
+ *
+ * Retrieve the return code from the pending queue. If IN_WAKEUP is found in
+ * q->status, then we must loop until the value is replaced with the final
+ * value: This may happen if a task is woken up by an unrelated event (e.g.
+ * signal) and in parallel the task is woken up by another task because it got
+ * the requested semaphores.
+ *
+ * The function can be called with or without holding the semaphore spinlock.
+ */
+static int get_queue_result(struct sem_queue *q)
+{
+ int error;
+
+ error = q->status;
+ while (unlikely(error == IN_WAKEUP)) {
+ cpu_relax();
+ error = q->status;
+ }
+
+ return error;
+}
+
+
SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
unsigned, nsops, const struct timespec __user *, timeout)
{
@@ -1409,15 +1436,18 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
else
schedule();
- error = queue.status;
- while(unlikely(error == IN_WAKEUP)) {
- cpu_relax();
- error = queue.status;
- }
+ error = get_queue_result(&queue);
if (error != -EINTR) {
/* fast path: update_queue already obtained all requested
- * resources */
+ * resources.
+ * Perform a smp_mb(): User space could assume that semop()
+ * is a memory barrier: Without the mb(), the cpu could
+ * speculatively read in user space stale data that was
+ * overwritten by the previous owner of the semaphore.
+ */
+ smp_mb();
+
goto out_free;
}
@@ -1427,10 +1457,12 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
goto out_free;
}
+ error = get_queue_result(&queue);
+
/*
* If queue.status != -EINTR we are woken up by another process
*/
- error = queue.status;
+
if (error != -EINTR) {
goto out_unlock_free;
}