From: Jeff Moyer Date: Tue, 2 Sep 2014 17:17:00 +0000 (-0400) Subject: aio: add missing smp_rmb() in read_events_ring X-Git-Tag: v3.17-rc4~21^2~1 X-Git-Url: https://asedeno.scripts.mit.edu/gitweb/?a=commitdiff_plain;h=2ff396be602f10b5eab8e73b24f20348fa2de159;p=linux.git aio: add missing smp_rmb() in read_events_ring 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 Cc: stable@vger.kernel.org --- diff --git a/fs/aio.c b/fs/aio.c index 97bc62cbe2da..5f2e9c6c328e 100644 --- a/fs/aio.c +++ b/fs/aio.c @@ -1111,6 +1111,12 @@ 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)