[RFCv7 PATCH 3/4] net/sock.h: use poll_does_not_wait() in sock_poll_wait()

From: Hans Verkuil
Date: Thu Feb 02 2012 - 05:35:26 EST

From: Hans Verkuil <hans.verkuil@xxxxxxxxx>

In order to determine whether poll_wait() might actually wait the
poll_table pointer was tested in sock_poll_wait(). This is no longer
sufficient, instead poll_does_not_wait() should be called. That function
also tests whether pt->pq_proc is non-NULL.

Without this change smp_mb() could be called unnecessarily in some
circumstances, causing a performance hit.

Signed-off-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
include/net/sock.h | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index 91c1c8b..da7f2ec 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1824,7 +1824,7 @@ static inline bool wq_has_sleeper(struct socket_wq *wq)
static inline void sock_poll_wait(struct file *filp,
wait_queue_head_t *wait_address, poll_table *p)
- if (p && wait_address) {
+ if (!poll_does_not_wait(p) && wait_address) {
poll_wait(filp, wait_address, p);
* We need to be sure we are in sync with the

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