|
 |
958e1b |
From 068000dc97228f85b878634e3d49d3354f5cbafe Mon Sep 17 00:00:00 2001
|
|
|
958e1b |
From: John Snow <jsnow@redhat.com>
|
|
|
958e1b |
Date: Fri, 11 Jul 2014 19:07:24 -0500
|
|
|
958e1b |
Subject: [CHANGE 20/29] aio: fix qemu_bh_schedule() bh->ctx race condition
|
|
|
958e1b |
To: rhvirt-patches@redhat.com,
|
|
|
958e1b |
jen@redhat.com
|
|
|
958e1b |
|
|
|
958e1b |
RH-Author: John Snow <jsnow@redhat.com>
|
|
|
958e1b |
Message-id: <1405105644-21039-1-git-send-email-jsnow@redhat.com>
|
|
|
958e1b |
Patchwork-id: 59866
|
|
|
958e1b |
O-Subject: [RHEL-7.1 qemu-kvm PATCH] aio: fix qemu_bh_schedule() bh->ctx race condition
|
|
|
958e1b |
Bugzilla: 1116728
|
|
|
958e1b |
RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>
|
|
|
958e1b |
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
|
|
|
958e1b |
RH-Acked-by: Fam Zheng <famz@redhat.com>
|
|
|
958e1b |
|
|
|
958e1b |
From: Stefan Hajnoczi <stefanha@redhat.com>
|
|
|
958e1b |
|
|
|
958e1b |
bz: https://bugzilla.redhat.com/show_bug.cgi?id=1116728
|
|
|
958e1b |
brew: https://brewweb.devel.redhat.com/taskinfo?taskID=7690195
|
|
|
958e1b |
upstream: 924fe1293c3e7a3c787bbdfb351e7f168caee3e9
|
|
|
958e1b |
|
|
|
958e1b |
qemu_bh_schedule() is supposed to be thread-safe at least the first time
|
|
|
958e1b |
it is called. Unfortunately this is not quite true:
|
|
|
958e1b |
|
|
|
958e1b |
bh->scheduled = 1;
|
|
|
958e1b |
aio_notify(bh->ctx);
|
|
|
958e1b |
|
|
|
958e1b |
Since another thread may run the BH callback once it has been scheduled,
|
|
|
958e1b |
there is a race condition if the callback frees the BH before
|
|
|
958e1b |
aio_notify(bh->ctx) has a chance to run.
|
|
|
958e1b |
|
|
|
958e1b |
Reported-by: Stefan Priebe <s.priebe@profihost.ag>
|
|
|
958e1b |
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
|
|
|
958e1b |
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
|
|
|
958e1b |
Tested-by: Stefan Priebe <s.priebe@profihost.ag>
|
|
|
958e1b |
(cherry picked from commit 924fe1293c3e7a3c787bbdfb351e7f168caee3e9)
|
|
|
958e1b |
Signed-off-by: John Snow <jsnow@redhat.com>
|
|
|
958e1b |
---
|
|
|
958e1b |
async.c | 14 ++++++++++----
|
|
|
958e1b |
1 file changed, 10 insertions(+), 4 deletions(-)
|
|
|
958e1b |
|
|
|
958e1b |
Signed-off-by: jen <jen@redhat.com>
|
|
|
958e1b |
---
|
|
|
958e1b |
async.c | 14 ++++++++++----
|
|
|
958e1b |
1 file changed, 10 insertions(+), 4 deletions(-)
|
|
|
958e1b |
|
|
|
958e1b |
diff --git a/async.c b/async.c
|
|
|
958e1b |
index 5ce3633..d7ec1ea 100644
|
|
|
958e1b |
--- a/async.c
|
|
|
958e1b |
+++ b/async.c
|
|
|
958e1b |
@@ -117,15 +117,21 @@ void qemu_bh_schedule_idle(QEMUBH *bh)
|
|
|
958e1b |
|
|
|
958e1b |
void qemu_bh_schedule(QEMUBH *bh)
|
|
|
958e1b |
{
|
|
|
958e1b |
+ AioContext *ctx;
|
|
|
958e1b |
+
|
|
|
958e1b |
if (bh->scheduled)
|
|
|
958e1b |
return;
|
|
|
958e1b |
+ ctx = bh->ctx;
|
|
|
958e1b |
bh->idle = 0;
|
|
|
958e1b |
- /* Make sure that idle & any writes needed by the callback are done
|
|
|
958e1b |
- * before the locations are read in the aio_bh_poll.
|
|
|
958e1b |
+ /* Make sure that:
|
|
|
958e1b |
+ * 1. idle & any writes needed by the callback are done before the
|
|
|
958e1b |
+ * locations are read in the aio_bh_poll.
|
|
|
958e1b |
+ * 2. ctx is loaded before scheduled is set and the callback has a chance
|
|
|
958e1b |
+ * to execute.
|
|
|
958e1b |
*/
|
|
|
958e1b |
- smp_wmb();
|
|
|
958e1b |
+ smp_mb();
|
|
|
958e1b |
bh->scheduled = 1;
|
|
|
958e1b |
- aio_notify(bh->ctx);
|
|
|
958e1b |
+ aio_notify(ctx);
|
|
|
958e1b |
}
|
|
|
958e1b |
|
|
|
958e1b |
|
|
|
958e1b |
--
|
|
|
958e1b |
1.9.3
|
|
|
958e1b |
|