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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.

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jiri Olsa 2009-07-08 12:10:31 +00:00 committed by David S. Miller
parent a57de0b433
commit ad46276952
3 changed files with 13 additions and 1 deletions
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4
arch/x86/include/asm/spinlock.h
View File

@ -302,4 +302,8 @@ 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. */
static inline void smp_mb__after_lock(void) { }
#define ARCH_HAS_SMP_MB_AFTER_LOCK
#endif /* _ASM_X86_SPINLOCK_H */

5
include/linux/spinlock.h
View File

@ -132,6 +132,11 @@ do { \
#endif /*__raw_spin_is_contended*/
#endif
/* The lock does not imply full memory barrier. */
#ifndef ARCH_HAS_SMP_MB_AFTER_LOCK
static inline void smp_mb__after_lock(void) { smp_mb(); }
#endif
/**
* spin_unlock_wait - wait until the spinlock gets unlocked
* @lock: the spinlock in question.

5
include/net/sock.h
View File

@ -1271,6 +1271,9 @@ static inline int sk_has_allocations(const struct sock *sk)
* in its cache, and so does the tp->rcv_nxt update on CPU2 side. The CPU1
* could then endup calling schedule and sleep forever if there are no more
* data on the socket.
*
* The sk_has_sleeper is always called right after a call to read_lock, so we
* can use smp_mb__after_lock barrier.
*/
static inline int sk_has_sleeper(struct sock *sk)
{
@ -1280,7 +1283,7 @@ static inline int sk_has_sleeper(struct sock *sk)
*
* This memory barrier is paired in the sock_poll_wait.
*/
smp_mb();
smp_mb__after_lock();
return sk->sk_sleep && waitqueue_active(sk->sk_sleep);
}