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Commit ad462769 authored by Jiri Olsa's avatar Jiri Olsa Committed by David S. Miller
Browse files

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: default avatarJiri Olsa <jolsa@redhat.com>
Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent a57de0b4

arch/x86/include/asm/spinlock.h

+4 −0
Original line number Diff line number Diff line
@@ -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 */

include/linux/spinlock.h

+5 −0
Original line number Diff line number Diff line
@@ -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.

include/net/sock.h

+4 −1
Original line number Diff line number Diff line
@@ -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);

}