+ ipc-semc-fix-complex_count-vs-simple-op-race-update.patch added to -mm tree

+ ipc-semc-fix-complex_count-vs-simple-op-race-update.patch added to -mm tree

[akpm]

The patch titled
     Subject: ipc-semc-fix-complex_count-vs-simple-op-race-update
has been added to the -mm tree.  Its filename is
     ipc-semc-fix-complex_count-vs-simple-op-race-update.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/ipc-semc-fix-complex_count-vs-simple-op-race-update.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/ipc-semc-fix-complex_count-vs-simple-op-race-update.patch

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------------------------------------------------------
From: Manfred Spraul <manfred@colorfullife.com>
Subject: ipc-semc-fix-complex_count-vs-simple-op-race-update

Link: http://lkml.kernel.org/r/1468386412-3608-2-git-send-email-manfred@colorfullife.com
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 ipc/sem.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff -puN ipc/sem.c~ipc-semc-fix-complex_count-vs-simple-op-race-update ipc/sem.c
--- a/ipc/sem.c~ipc-semc-fix-complex_count-vs-simple-op-race-update
+++ a/ipc/sem.c
@@ -291,6 +291,14 @@ static void complexmode_enter(struct sem
 		sem = sma->sem_base + i;
 		spin_unlock_wait(&sem->lock);
 	}
+	/*
+	 * spin_unlock_wait() is not a memory barriers, it is only a
+	 * control barrier. The code must pair with spin_unlock(&sem->lock),
+	 * thus just the control barrier is insufficient.
+	 *
+	 * smp_rmb() is sufficient, as writes cannot pass the control barrier.
+	 */
+	smp_rmb();
 }
 
 /*
@@ -346,7 +354,7 @@ static inline int sem_lock(struct sem_ar
 
 	/*
 	 * Initial check for complex_mode. Just an optimization,
-	 * no locking.
+	 * no locking, no memory barrier.
 	 */
 	if (!READ_ONCE(sma->complex_mode)) {
 		/*
@@ -361,7 +369,7 @@ static inline int sem_lock(struct sem_ar
 		 */
 		smp_mb();
 
-		if (!READ_ONCE(sma->complex_mode)) {
+		if (!smp_load_acquire(&sma->complex_mode)) {
 			/* fast path successful! */
 			return sops->sem_num;
 		}
_

Patches currently in -mm which might be from manfred@colorfullife.com are

ipc-semc-fix-complex_count-vs-simple-op-race.patch
ipc-semc-fix-complex_count-vs-simple-op-race-update.patch
ipc-semc-remove-duplicated-memory-barriers.patch
ipc-sem-sem_lock-with-hysteresis.patch