[ 47/48] futex: Unlock hb->lock in futex_wait_requeue_pi()

From: Willy Tarreau
Date: Sun Nov 16 2014 - 17:09:43 EST

2.6.32-longterm review patch. If anyone has any objections, please let me know.

error path

From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

futex_wait_requeue_pi() calls futex_wait_setup(). If
futex_wait_setup() succeeds it returns with hb->lock held and
preemption disabled. Now the sanity check after this does:

if (match_futex(&q.key, &key2)) {
ret = -EINVAL;
goto out_put_keys;

which releases the keys but does not release hb->lock.

So we happily return to user space with hb->lock held and therefor
preemption disabled.

Unlock hb->lock before taking the exit route.

Reported-by: Dave "Trinity" Jones <davej@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Darren Hart <dvhart@xxxxxxxxxxxxxxx>
Reviewed-by: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1409112318500.4178@nanos
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
(cherry picked from commit 13c42c2f43b19aab3195f2d357db00d1e885eaa8)
[wt: 2.6.32 needs &q as first argument of queue_unlock()]
Signed-off-by: Willy Tarreau <w@xxxxxx>
kernel/futex.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/kernel/futex.c b/kernel/futex.c
index 55dd3d2..1e092d3 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2414,6 +2414,7 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared,
* shared futexes. We need to compare the keys:
if (match_futex(&q.key, &key2)) {
+ queue_unlock(&q, hb);
ret = -EINVAL;
goto out_put_keys;

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