This patch seems to fix my issue with ppoll() being stuck on my SMP machine: http://article.gmane.org/gmane.linux.file-systems/70414 The change to sock_poll_wait() in commit 626cf236608505d376e4799adb4f7eb00a8594af (poll: add poll_requested_events() and poll_does_not_wait() functions) seems to have allowed additional cases where the SMP memory barrier is not issued before checking for readiness. In my case, this affects the select()-family of functions which register descriptors once and set _qproc to NULL before checking events again (after poll_schedule_timeout() returns). The set_mb() barrier in poll_schedule_timeout() appears to be insufficient on my SMP x86-64 machine (as it's only an xchg()). This may also be related to the epoll issue described by Andreas Voellmy in http://thread.gmane.org/gmane.linux.kernel/1408782/ Signed-off-by: Eric Wong <normalperson@xxxxxxxx> Cc: Hans Verkuil <hans.verkuil@xxxxxxxxx> Cc: Jiri Olsa <jolsa@xxxxxxxxxx> Cc: Jonathan Corbet <corbet@xxxxxxx> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Davide Libenzi <davidel@xxxxxxxxxxxxxxx> Cc: Hans de Goede <hdegoede@xxxxxxxxxx> Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxx> Cc: David Miller <davem@xxxxxxxxxxxxx> Cc: Eric Dumazet <eric.dumazet@xxxxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Andreas Voellmy <andreas.voellmy@xxxxxxxx> Cc: "Junchang(Jason) Wang" <junchang.wang@xxxxxxxx> Cc: netdev@xxxxxxxxxxxxxxx Cc: linux-fsdevel@xxxxxxxxxxxxxxx --- If this patch is correct, I think we can just drop the poll_does_not_wait() function entirely since poll_wait() does the same check anyways... include/net/sock.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/include/net/sock.h b/include/net/sock.h index c945fba..1923e48 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -1925,8 +1925,9 @@ 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 (!poll_does_not_wait(p) && wait_address) { - poll_wait(filp, wait_address, p); + if (wait_address) { + if (!poll_does_not_wait(p)) + poll_wait(filp, wait_address, p); /* We need to be sure we are in sync with the * socket flags modification. * -- Eric Wong -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
