[patch 03/26] rt-mutex: Fix stale return value


-stable review patch. If anyone has any objections, please let us know.

------------------

Alexey Kuznetsov found some problems in the pi-futex code.

The major problem is a stale return value in rt_mutex_slowlock():

When the pi chain walk returns -EDEADLK, but the waiter was woken up
during the phases where the locks were dropped, the rtmutex could be
acquired, but due to the stale return value -EDEADLK returned to the
caller.

Reset the return value in the woken up path.

Cc: Alexey Kuznetsov <kuznet@xxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Chris Wright <chrisw@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
kernel/rtmutex.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

--- linux-2.6.21.6.orig/kernel/rtmutex.c
+++ linux-2.6.21.6/kernel/rtmutex.c
@@ -659,9 +659,16 @@ rt_mutex_slowlock(struct rt_mutex *lock,
* all over without going into schedule to try
* to get the lock now:
*/
- if (unlikely(!waiter.task))
+ if (unlikely(!waiter.task)) {
+ /*
+ * Reset the return value. We might
+ * have returned with -EDEADLK and the
+ * owner released the lock while we
+ * were walking the pi chain.
+ */
+ ret = 0;
continue;
-
+ }
if (unlikely(ret))
break;
}

--
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

Relevant Pages

  • [2.6.20.16 review 10/28] rt-mutex: Fix stale return value
    ... The major problem is a stale return value in rt_mutex_slowlock: ... When the pi chain walk returns -EDEADLK, but the waiter was woken up ... during the phases where the locks were dropped, ...
    (Linux-Kernel)
  • [patch-stable 1/3] rt-mutex: Fix stale return value
    ... The major problem is a stale return value in rt_mutex_slowlock: ... When the pi chain walk returns -EDEADLK, but the waiter was woken up ... during the phases where the locks were dropped, ...
    (Linux-Kernel)
  • [patch 1/4] rt-mutex: Fix stale return value
    ... The major problem is a stale return value in rt_mutex_slowlock: ... When the pi chain walk returns -EDEADLK, but the waiter was woken up ... during the phases where the locks were dropped, ...
    (Linux-Kernel)