This is a note to let you know that I've just added the patch titled
aio: add missing smp_rmb() in read_events_ring
to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
aio-add-missing-smp_rmb-in-read_events_ring.patch
and it can be found in the queue-3.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 2ff396be602f10b5eab8e73b24f20348fa2de159 Mon Sep 17 00:00:00 2001
From: Jeff Moyer <jmoyer@xxxxxxxxxx>
Date: Tue, 2 Sep 2014 13:17:00 -0400
Subject: aio: add missing smp_rmb() in read_events_ring
From: Jeff Moyer <jmoyer@xxxxxxxxxx>
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 <jmoyer@xxxxxxxxxx>
Signed-off-by: Benjamin LaHaise <bcrl@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/aio.c | 6 ++++++
1 file changed, 6 insertions(+)
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1134,6 +1134,12 @@ static long aio_read_events_ring(struct
tail = ring->tail;
kunmap_atomic(ring);
+ /*
+ * 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();
+
pr_debug("h%u t%u m%u\n", head, tail, ctx->nr_events);
if (head == tail)
Patches currently in stable-queue which might be from jmoyer@xxxxxxxxxx are
queue-3.14/aio-add-missing-smp_rmb-in-read_events_ring.patch
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