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authorDavidlohr Bueso <dave@stgolabs.net>2016-12-14 15:06:46 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2016-12-14 16:04:08 -0800
commitb5fa01a22e4ba9e3ca6de7cb94c3d21e42da449c (patch)
tree2fcea15a5c609e51abf25e6cff6e1630627ed068 /ipc
parentf150f02cfbc7b6b980e260856555abd73235a6b0 (diff)
ipc/sem: simplify wait-wake loop
Instead of using the reverse goto, we can simplify the flow and make it more language natural by just doing do-while instead. One would hope this is the standard way (or obviously just with a while bucle) that we do wait/wakeup handling in the kernel. The exact same logic is kept, just more indented. [akpm@linux-foundation.org: coding-style fixes] Link: http://lkml.kernel.org/r/1478708774-28826-2-git-send-email-dave@stgolabs.net Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Cc: Manfred Spraul <manfred@colorfullife.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'ipc')
-rw-r--r--ipc/sem.c108
1 files changed, 52 insertions, 56 deletions
diff --git a/ipc/sem.c b/ipc/sem.c
index 4f5af6e7d630..a82c88d0900f 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -1963,71 +1963,67 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
sma->complex_count++;
}
-sleep_again:
- queue.status = -EINTR;
- queue.sleeper = current;
+ do {
+ queue.status = -EINTR;
+ queue.sleeper = current;
- __set_current_state(TASK_INTERRUPTIBLE);
- sem_unlock(sma, locknum);
- rcu_read_unlock();
+ __set_current_state(TASK_INTERRUPTIBLE);
+ sem_unlock(sma, locknum);
+ rcu_read_unlock();
- if (timeout)
- jiffies_left = schedule_timeout(jiffies_left);
- else
- schedule();
+ if (timeout)
+ jiffies_left = schedule_timeout(jiffies_left);
+ else
+ schedule();
- /*
- * fastpath: the semop has completed, either successfully or not, from
- * the syscall pov, is quite irrelevant to us at this point; we're done.
- *
- * We _do_ care, nonetheless, about being awoken by a signal or
- * spuriously. The queue.status is checked again in the slowpath (aka
- * after taking sem_lock), such that we can detect scenarios where we
- * were awakened externally, during the window between wake_q_add() and
- * wake_up_q().
- */
- error = READ_ONCE(queue.status);
- if (error != -EINTR) {
/*
- * 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.
+ * fastpath: the semop has completed, either successfully or
+ * not, from the syscall pov, is quite irrelevant to us at this
+ * point; we're done.
+ *
+ * We _do_ care, nonetheless, about being awoken by a signal or
+ * spuriously. The queue.status is checked again in the
+ * slowpath (aka after taking sem_lock), such that we can detect
+ * scenarios where we were awakened externally, during the
+ * window between wake_q_add() and wake_up_q().
*/
- smp_mb();
- goto out_free;
- }
-
- rcu_read_lock();
- sma = sem_obtain_lock(ns, semid, sops, nsops, &locknum);
- error = READ_ONCE(queue.status);
+ error = READ_ONCE(queue.status);
+ if (error != -EINTR) {
+ /*
+ * User space could assume that semop() is a memory
+ * barrier: Without the mb(), the cpu could
+ * speculatively read in userspace stale data that was
+ * overwritten by the previous owner of the semaphore.
+ */
+ smp_mb();
+ goto out_free;
+ }
- /*
- * Array removed? If yes, leave without sem_unlock().
- */
- if (IS_ERR(sma)) {
- rcu_read_unlock();
- goto out_free;
- }
+ rcu_read_lock();
+ sma = sem_obtain_lock(ns, semid, sops, nsops, &locknum);
+ error = READ_ONCE(queue.status);
- /*
- * If queue.status != -EINTR we are woken up by another process.
- * Leave without unlink_queue(), but with sem_unlock().
- */
- if (error != -EINTR)
- goto out_unlock_free;
+ /*
+ * Array removed? If yes, leave without sem_unlock().
+ */
+ if (IS_ERR(sma)) {
+ rcu_read_unlock();
+ goto out_free;
+ }
- /*
- * If an interrupt occurred we have to clean up the queue.
- */
- if (timeout && jiffies_left == 0)
- error = -EAGAIN;
+ /*
+ * If queue.status != -EINTR we are woken up by another process.
+ * Leave without unlink_queue(), but with sem_unlock().
+ */
+ if (error != -EINTR)
+ goto out_unlock_free;
- /*
- * If the wakeup was spurious, just retry.
- */
- if (error == -EINTR && !signal_pending(current))
- goto sleep_again;
+ /*
+ * If an interrupt occurred we have to clean up the queue.
+ */
+ if (timeout && jiffies_left == 0)
+ error = -EAGAIN;
+ } while (error == -EINTR && !signal_pending(current)); /* spurious */
unlink_queue(sma, &queue);

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