This is a note to let you know that I've just added the patch titled
ipc/sem.c: optimize sem_lock()
to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
ipc-sem.c-optimize-sem_lock.patch
and it can be found in the queue-3.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 6d07b68ce16ae9535955ba2059dedba5309c3ca1 Mon Sep 17 00:00:00 2001
From: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Date: Mon, 30 Sep 2013 13:45:06 -0700
Subject: ipc/sem.c: optimize sem_lock()
From: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
commit 6d07b68ce16ae9535955ba2059dedba5309c3ca1 upstream.
Operations that need access to the whole array must guarantee that there
are no simple operations ongoing. Right now this is achieved by
spin_unlock_wait(sem->lock) on all semaphores.
If complex_count is nonzero, then this spin_unlock_wait() is not
necessary, because it was already performed in the past by the thread
that increased complex_count and even though sem_perm.lock was dropped
inbetween, no simple operation could have started, because simple
operations cannot start when complex_count is non-zero.
Signed-off-by: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Cc: Mike Galbraith <bitbucket@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Reviewed-by: Davidlohr Bueso <davidlohr@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
ipc/sem.c | 8 ++++++++
1 file changed, 8 insertions(+)
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -257,12 +257,20 @@ static void sem_rcu_free(struct rcu_head
* Caller must own sem_perm.lock.
* New simple ops cannot start, because simple ops first check
* that sem_perm.lock is free.
+ * that a) sem_perm.lock is free and b) complex_count is 0.
*/
static void sem_wait_array(struct sem_array *sma)
{
int i;
struct sem *sem;
+ if (sma->complex_count) {
+ /* The thread that increased sma->complex_count waited on
+ * all sem->lock locks. Thus we don't need to wait again.
+ */
+ return;
+ }
+
for (i = 0; i < sma->sem_nsems; i++) {
sem = sma->sem_base + i;
spin_unlock_wait(&sem->lock);
Patches currently in stable-queue which might be from manfred@xxxxxxxxxxxxxxxx are
queue-3.10/ipc-drop-ipc_lock_by_ptr.patch
queue-3.10/ipc-sem.c-synchronize-the-proc-interface.patch
queue-3.10/ipc-msg-drop-msg_unlock.patch
queue-3.10/ipc-fix-race-with-lsms.patch
queue-3.10/ipc-shm-shorten-critical-region-in-shmctl_down.patch
queue-3.10/ipc-rename-ids-rw_mutex.patch
queue-3.10/ipc-msg.c-fix-lost-wakeup-in-msgsnd.patch
queue-3.10/ipc-shm-introduce-lockless-functions-to-obtain-the-ipc-object.patch
queue-3.10/ipc-sem.c-optimize-sem_lock.patch
queue-3.10/ipc-shm-shorten-critical-region-for-shmat.patch
queue-3.10/ipc-sem.c-fix-race-in-sem_lock.patch
queue-3.10/ipc-sem-separate-wait-for-zero-and-alter-tasks-into-seperate-queues.patch
queue-3.10/ipc-shm-shorten-critical-region-for-shmctl.patch
queue-3.10/ipc-shm-introduce-shmctl_nolock.patch
queue-3.10/ipc-drop-ipcctl_pre_down.patch
queue-3.10/ipc-document-general-ipc-locking-scheme.patch
queue-3.10/ipc-util.c-ipc_rcu_alloc-cacheline-align-allocation.patch
queue-3.10/ipc-shm-drop-shm_lock_check.patch
queue-3.10/ipc-sem.c-cacheline-align-the-semaphore-structures.patch
queue-3.10/ipc-msg-prevent-race-with-rmid-in-msgsnd-msgrcv.patch
queue-3.10/ipc-shm-guard-against-non-existant-vma-in-shmdt-2.patch
queue-3.10/ipc-sem.c-always-use-only-one-queue-for-alter-operations.patch
queue-3.10/ipc-shm-cleanup-do_shmat-pasta.patch
queue-3.10/ipc-drop-ipc_lock_check.patch
queue-3.10/ipc-sem.c-update-sem_otime-for-all-operations.patch
queue-3.10/ipc-sem.c-rename-try_atomic_semop-to-perform_atomic_semop-docu-update.patch
queue-3.10/ipc-shm-make-shmctl_nolock-lockless.patch
queue-3.10/ipc-sem.c-replace-shared-sem_otime-with-per-semaphore-value.patch
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