From 0e8c665699e953fa58dc1b0b0d09e5dce7343cc7 Mon Sep 17 00:00:00 2001 From: Manfred Spraul Date: Mon, 30 Sep 2013 13:45:25 -0700 Subject: [PATCH] ipc/sem.c: update sem_otime for all operations In commit 0a2b9d4c7967 ("ipc/sem.c: move wake_up_process out of the spinlock section"), the update of semaphore's sem_otime(last semop time) was moved to one central position (do_smart_update). But since do_smart_update() is only called for operations that modify the array, this means that wait-for-zero semops do not update sem_otime anymore. The fix is simple: Non-alter operations must update sem_otime. [akpm@linux-foundation.org: coding-style fixes] Signed-off-by: Manfred Spraul Reported-by: Jia He Tested-by: Jia He Cc: Davidlohr Bueso Cc: Mike Galbraith Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- ipc/sem.c | 42 +++++++++++++++++++++++++++++------------- 1 file changed, 29 insertions(+), 13 deletions(-) diff --git a/ipc/sem.c b/ipc/sem.c index cd6a733011a2..8c4f59b0204a 100644 --- a/ipc/sem.c +++ b/ipc/sem.c @@ -917,6 +917,24 @@ again: return semop_completed; } +/** + * set_semotime(sma, sops) - set sem_otime + * @sma: semaphore array + * @sops: operations that modified the array, may be NULL + * + * sem_otime is replicated to avoid cache line trashing. + * This function sets one instance to the current time. + */ +static void set_semotime(struct sem_array *sma, struct sembuf *sops) +{ + if (sops == NULL) { + sma->sem_base[0].sem_otime = get_seconds(); + } else { + sma->sem_base[sops[0].sem_num].sem_otime = + get_seconds(); + } +} + /** * do_smart_update(sma, sops, nsops, otime, pt) - optimized update_queue * @sma: semaphore array @@ -967,17 +985,10 @@ static void do_smart_update(struct sem_array *sma, struct sembuf *sops, int nsop } } } - if (otime) { - if (sops == NULL) { - sma->sem_base[0].sem_otime = get_seconds(); - } else { - sma->sem_base[sops[0].sem_num].sem_otime = - get_seconds(); - } - } + if (otime) + set_semotime(sma, sops); } - /* 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 @@ -1839,12 +1850,17 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops, error = perform_atomic_semop(sma, sops, nsops, un, task_tgid_vnr(current)); - if (error <= 0) { - if (alter && error == 0) + if (error == 0) { + /* If the operation was successful, then do + * the required updates. + */ + if (alter) do_smart_update(sma, sops, nsops, 1, &tasks); - - goto out_unlock_free; + else + set_semotime(sma, sops); } + if (error <= 0) + goto out_unlock_free; /* We need to sleep on this operation, so we put the current * task into the pending queue and go to sleep. -- 2.20.1