The patch titled
Subject: ipc/sem: do not call wake_sem_queue_do() prematurely
has been added to the -mm tree. Its filename is
ipc-sem-do-not-call-wake_sem_queue_do-prematurely.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/ipc-sem-do-not-call-wake_sem_queue_do-prematurely.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/ipc-sem-do-not-call-wake_sem_queue_do-prematurely.patch
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From: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Subject: ipc/sem: do not call wake_sem_queue_do() prematurely
... as this call should obviously be paired with its _prepare()
counterpart. At least whenever possible, as there is no harm in
calling it bogusly as we do now in a few places. Immediate error
semop(2) paths that are far from ever having the task block can
be simplified and avoid a few unnecessary loads on their way out
of the call as it is not deeply nested.
Link: http://lkml.kernel.org/r/1474225896-10066-2-git-send-email-dave@xxxxxxxxxxxx
Signed-off-by: Davidlohr Bueso <dbueso@xxxxxxx>
Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
ipc/sem.c | 19 ++++++++++++-------
1 file changed, 12 insertions(+), 7 deletions(-)
diff -puN ipc/sem.c~ipc-sem-do-not-call-wake_sem_queue_do-prematurely ipc/sem.c
--- a/ipc/sem.c~ipc-sem-do-not-call-wake_sem_queue_do-prematurely
+++ a/ipc/sem.c
@@ -1904,16 +1904,22 @@ SYSCALL_DEFINE4(semtimedop, int, semid,
}
error = -EFBIG;
- if (max >= sma->sem_nsems)
- goto out_rcu_wakeup;
+ if (max >= sma->sem_nsems) {
+ rcu_read_unlock();
+ goto out_free;
+ }
error = -EACCES;
- if (ipcperms(ns, &sma->sem_perm, alter ? S_IWUGO : S_IRUGO))
- goto out_rcu_wakeup;
+ if (ipcperms(ns, &sma->sem_perm, alter ? S_IWUGO : S_IRUGO)) {
+ rcu_read_unlock();
+ goto out_free;
+ }
error = security_sem_semop(sma, sops, nsops, alter);
- if (error)
- goto out_rcu_wakeup;
+ if (error) {
+ rcu_read_unlock();
+ goto out_free;
+ }
error = -EIDRM;
locknum = sem_lock(sma, sops, nsops);
@@ -2056,7 +2062,6 @@ sleep_again:
out_unlock_free:
sem_unlock(sma, locknum);
-out_rcu_wakeup:
rcu_read_unlock();
wake_up_sem_queue_do(&tasks);
out_free:
_
Patches currently in -mm which might be from dave@xxxxxxxxxxxx are
ipc-sem-do-not-call-wake_sem_queue_do-prematurely.patch
ipc-sem-rework-task-wakeups.patch
ipc-sem-optimize-perform_atomic_semop.patch
ipc-sem-explicitly-inline-check_restart.patch
ipc-sem-use-proper-list-api-for-pending_list-wakeups.patch
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