linux-kernel - [PATCH 2/2] memory barrier: adding smp_mb__after

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Message-ID: <20090629141559.GG3845@jolsa.lab.eng.brq.redhat.com>
Date:	Mon, 29 Jun 2009 16:15:59 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	netdev@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, fbl@...hat.com, nhorman@...hat.com,
	davem@...hat.com, htejun@...il.com, jarkao2@...il.com,
	oleg@...hat.com, davidel@...ilserver.org, eric.dumazet@...il.com
Subject: [PATCH 2/2] memory barrier: adding smp_mb__after_lock


Adding smp_mb__after_lock define to be used as a smp_mb call after
a lock.  

Making it nop for x86, since {read|write|spin}_lock() on x86 are 
full memory barriers.

wbr,
jirka


Signed-off-by: Jiri Olsa <jolsa@...hat.com>

---
 arch/x86/include/asm/spinlock.h |    3 +++
 include/linux/spinlock.h        |    5 +++++
 include/net/sock.h              |    2 +-
 3 files changed, 9 insertions(+), 1 deletions(-)

diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index b7e5db8..39ecc5f 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -302,4 +302,7 @@ static inline void __raw_write_unlock(raw_rwlock_t *rw)
 #define _raw_read_relax(lock)	cpu_relax()
 #define _raw_write_relax(lock)	cpu_relax()
 
+/* The {read|write|spin}_lock() on x86 are full memory barriers. */
+#define smp_mb__after_lock() do { } while (0)
+
 #endif /* _ASM_X86_SPINLOCK_H */
diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h
index 252b245..ae053bd 100644
--- a/include/linux/spinlock.h
+++ b/include/linux/spinlock.h
@@ -132,6 +132,11 @@ do {								\
 #endif /*__raw_spin_is_contended*/
 #endif
 
+/* The lock does not imply full memory barrier. */
+#ifndef smp_mb__after_lock
+#define smp_mb__after_lock() smp_mb()
+#endif
+
 /**
  * spin_unlock_wait - wait until the spinlock gets unlocked
  * @lock: the spinlock in question.
diff --git a/include/net/sock.h b/include/net/sock.h
index e9137ed..05fbf8b 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1277,7 +1277,7 @@ static inline void sock_poll_wait(struct file *filp, struct sock *sk,
 		 *
 		 * This memory barrier is paired in the sk_has_sleeper.
 		*/
-		smp_mb();
+		smp_mb__after_lock();
 	}
 }
 
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