From 42dd6eb155777748a1c8637614f9a03c9ebc69b6 Mon Sep 17 00:00:00 2001 From: Jeff Moyer Date: Tue, 2 Sep 2014 13:17:00 -0400 Subject: aio: add missing smp_rmb() in read_events_ring 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 Signed-off-by: Greg Kroah-Hartman --- fs/aio.c | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'fs') diff --git a/fs/aio.c b/fs/aio.c index c6c6845c7d1..c4b6b828825 100644 --- a/fs/aio.c +++ b/fs/aio.c @@ -1134,6 +1134,12 @@ static long aio_read_events_ring(struct kioctx *ctx, 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) -- cgit v1.2.3