Messages in this thread | | | Date | Thu, 09 Jul 2009 06:25:55 +0200 | From | Eric Dumazet <> | Subject | Re: [PATCHv7 2/2] memory barrier: adding smp_mb__after_lock |
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Jiri Olsa a écrit : > 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>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.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(-) > > diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h > index b7e5db8..4e77853 100644 > --- a/arch/x86/include/asm/spinlock.h > +++ b/arch/x86/include/asm/spinlock.h > @@ -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 */ > diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h > index 252b245..4be57ab 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 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. > diff --git a/include/net/sock.h b/include/net/sock.h > index 4eb8409..2c0da92 100644 > --- a/include/net/sock.h > +++ b/include/net/sock.h > @@ -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); > } >
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