linux-kernel - [PATCH] percpu-rwsem: use barrier in unlock path

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Date:	Tue, 16 Oct 2012 19:30:49 -0400 (EDT)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org
Subject: [PATCH] percpu-rwsem: use barrier in unlock path

Hi

When I read my patch 62ac665ff9fc07497ca524bd20d6a96893d11071 again, it 
turns out that it is missing a barrier in percpu_up_write. Please apply 
this.

Mikulas

---

percpu-rwsem: use barrier in unlock path

Fix missing barrier in patch 62ac665ff9fc07497ca524bd20d6a96893d11071.

The lock is considered unlocked when p->locked is set to false.
Use barrier prevent reordering of operations around p->locked.

Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>

---
 include/linux/percpu-rwsem.h |    9 +++++++++
 1 file changed, 9 insertions(+)

Index: linux-3.6.2-fast/include/linux/percpu-rwsem.h
===================================================================
--- linux-3.6.2-fast.orig/include/linux/percpu-rwsem.h	2012-10-17 01:17:55.000000000 +0200
+++ linux-3.6.2-fast/include/linux/percpu-rwsem.h	2012-10-17 01:21:46.000000000 +0200
@@ -66,6 +66,15 @@ static inline void percpu_down_write(str
 
 static inline void percpu_up_write(struct percpu_rw_semaphore *p)
 {
+	/*
+	 * The lock is considered unlocked when p->locked is set to false.
+	 * Use barrier prevent reordering of operations around p->locked.
+	 */
+#if defined(CONFIG_X86) && (!defined(CONFIG_X86_PPRO_FENCE) && !defined(CONFIG_X86_OOSTORE))
+	barrier();
+#else
+	smp_mb();
+#endif
 	p->locked = false;
 	mutex_unlock(&p->mtx);
 }

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