[PATCH] [BZ #16892] Check value of futex before updating in __lll_timedlock

[Bernard Ogden]

Retrying with git send-email. Patch unchanged other than whitespace fix.

2014-08-07  Bernard Ogden  <bernie.ogden@linaro.org>
	[BZ #16892]
	* sysdeps/nptl/lowlevellock.h (__lll_timedlock): Use
	atomic_compare_and_exchange_bool_acq rather than atomic_exchange_acq.

---

diff --git a/sysdeps/nptl/lowlevellock.h b/sysdeps/nptl/lowlevellock.h
index 548a9c8..28f4ba3 100644
--- a/sysdeps/nptl/lowlevellock.h
+++ b/sysdeps/nptl/lowlevellock.h
@@ -88,12 +88,15 @@ extern int __lll_timedlock_wait (int *futex, const struct timespec *,
 extern int __lll_robust_timedlock_wait (int *futex, const struct timespec *,
 					int private) attribute_hidden;
 
+/* Take futex if it is untaken.
+   Otherwise block until either we get the futex or abstime runs out.  */
 #define __lll_timedlock(futex, abstime, private)                \
   ({                                                            \
     int *__futex = (futex);                                     \
     int __val = 0;                                              \
                                                                 \
-    if (__glibc_unlikely (atomic_exchange_acq (__futex, 1)))    \
+    if (__glibc_unlikely                                        \
+        (atomic_compare_and_exchange_bool_acq (__futex, 1, 0))) \
       __val = __lll_timedlock_wait (__futex, abstime, private); \
     __val;                                                      \
   })