@@ -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 */
@@ -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.
@@ -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);
}
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@redhat.com> --- arch/x86/include/asm/spinlock.h | 4 ++++ include/linux/spinlock.h | 5 +++++ include/net/sock.h | 5 ++++- 3 files changed, 13 insertions(+), 1 deletions(-)