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authorPeter Zijlstra <peterz@infradead.org>2016-05-24 13:17:12 +0200
committerIngo Molnar <mingo@kernel.org>2016-06-14 11:55:14 +0200
commit33ac279677dcc2441cb93d8cb9cf7a74df62814d (patch)
treebcf918587b2425d1294b780b31ab67761e068e26 /ipc
parent1f03e8d2919270bd6ef64f39a45ce8df8a9f012a (diff)
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locking/barriers: Introduce smp_acquire__after_ctrl_dep()
Introduce smp_acquire__after_ctrl_dep(), this construct is not uncommon, but the lack of this barrier is. Use it to better express smp_rmb() uses in WRITE_ONCE(), the IPC semaphore code and the qspinlock code. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'ipc')
-rw-r--r--ipc/sem.c14
1 files changed, 2 insertions, 12 deletions
diff --git a/ipc/sem.c b/ipc/sem.c
index b3757ea0694b..84dff3df11a4 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -260,16 +260,6 @@ static void sem_rcu_free(struct rcu_head *head)
}
/*
- * spin_unlock_wait() and !spin_is_locked() are not memory barriers, they
- * are only control barriers.
- * The code must pair with spin_unlock(&sem->lock) or
- * spin_unlock(&sem_perm.lock), thus just the control barrier is insufficient.
- *
- * smp_rmb() is sufficient, as writes cannot pass the control barrier.
- */
-#define ipc_smp_acquire__after_spin_is_unlocked() smp_rmb()
-
-/*
* Wait until all currently ongoing simple ops have completed.
* Caller must own sem_perm.lock.
* New simple ops cannot start, because simple ops first check
@@ -292,7 +282,7 @@ static void sem_wait_array(struct sem_array *sma)
sem = sma->sem_base + i;
spin_unlock_wait(&sem->lock);
}
- ipc_smp_acquire__after_spin_is_unlocked();
+ smp_acquire__after_ctrl_dep();
}
/*
@@ -350,7 +340,7 @@ static inline int sem_lock(struct sem_array *sma, struct sembuf *sops,
* complex_count++;
* spin_unlock(sem_perm.lock);
*/
- ipc_smp_acquire__after_spin_is_unlocked();
+ smp_acquire__after_ctrl_dep();
/*
* Now repeat the test of complex_count: