Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752418AbaKAWlB (ORCPT ); Sat, 1 Nov 2014 18:41:01 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:60344 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751838AbaKAWjd (ORCPT ); Sat, 1 Nov 2014 18:39:33 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Benjamin LaHaise" , "Jeff Moyer" Date: Sat, 01 Nov 2014 22:28:03 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 022/102] aio: add missing smp_rmb() in read_events_ring In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.249 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2.64-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Jeff Moyer commit 2ff396be602f10b5eab8e73b24f20348fa2de159 upstream. We ran into a case on ppc64 running mariadb where io_getevents would return zeroed out I/O events. After adding instrumentation, it became clear that there was some missing synchronization between reading the tail pointer and the events themselves. This small patch fixes the problem in testing. Thanks to Zach for helping to look into this, and suggesting the fix. Signed-off-by: Jeff Moyer Signed-off-by: Benjamin LaHaise [bwh: Backported to 3.2: adjust context, indentation] Signed-off-by: Ben Hutchings --- fs/aio.c | 6 ++++++ 1 file changed, 6 insertions(+) --- a/fs/aio.c +++ b/fs/aio.c @@ -1102,6 +1102,13 @@ static int aio_read_evt(struct kioctx *i head = ring->head % info->nr; if (head != ring->tail) { struct io_event *evp = aio_ring_event(info, head, KM_USER1); + + /* + * Ensure that once we've read the current tail pointer, that + * we also see the events that were stored up to the tail. + */ + smp_rmb(); + *ent = *evp; head = (head + 1) % info->nr; smp_mb(); /* finish reading the event before updatng the head */ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/