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 <normalper...@yhbt.net> Cc: Hans Verkuil <hans.verk...@cisco.com> Cc: Jiri Olsa <jo...@redhat.com> Cc: Jonathan Corbet <cor...@lwn.net> Cc: Al Viro <v...@zeniv.linux.org.uk> Cc: Davide Libenzi <davi...@xmailserver.org> Cc: Hans de Goede <hdego...@redhat.com> Cc: Mauro Carvalho Chehab <mche...@infradead.org> Cc: David Miller <da...@davemloft.net> Cc: Eric Dumazet <eric.duma...@gmail.com> Cc: Andrew Morton <a...@linux-foundation.org> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Andreas Voellmy <andreas.voel...@yale.edu> Cc: "Junchang(Jason) Wang" <junchang.w...@yale.edu> Cc: net...@vger.kernel.org Cc: linux-fsde...@vger.kernel.org --- 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-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
