1 files changed, 10 insertions, 3 deletions

diff --git a/ipc/sem.c b/ipc/sem.c
index 53c3310f41c6..6115146563f9 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -326,10 +326,17 @@ static inline int sem_lock(struct sem_array *sma, struct sembuf *sops,
 
                 /* Then check that the global lock is free */
                 if (!spin_is_locked(&sma->sem_perm.lock)) {
-                        /* spin_is_locked() is not a memory barrier */
-                        smp_mb();
+                        /*
+                         * The ipc object lock check must be visible on all
+                         * cores before rechecking the complex count.  Otherwise
+                         * we can race with  another thread that does:
+                         *      complex_count++;
+                         *      spin_unlock(sem_perm.lock);
+                         */
+                        smp_rmb();
 
-                        /* Now repeat the test of complex_count:
+                        /*
+                         * Now repeat the test of complex_count:
                          * It can't change anymore until we drop sem->lock.
                          * Thus: if is now 0, then it will stay 0.
                          */