mutex: Fix robust mutex lock acquire (Bug 21778)

65810f0ef05e8c9e333f17a44e77808b163ca298 fixed a robust mutex bug but
introduced BZ 21778: if the CAS used to try to acquire a lock fails, the
expected value is not updated, which breaks other cases in the loce
acquisition loop.  The fix is to simply update the expected value with
the value returned by the CAS, which ensures that behavior is as if the
first case with the CAS never happened (if the CAS fails).

This is a regression introduced in the last release.

Tested on x86_64, i686, ppc64, ppc64le, s390x, aarch64, armv7hl.

1 files changed, 7 insertions, 0 deletions

diff --git a/nptl/tst-mutex7robust.c b/nptl/tst-mutex7robust.c
new file mode 100644
index 0000000000..8221a61d29
--- /dev/null
+++ b/nptl/tst-mutex7robust.c
@@ -0,0 +1,7 @@
+/* Bug 21778: Fix oversight in robust mutex lock acquisition.  */
+#define TYPE PTHREAD_MUTEX_NORMAL
+#define ROBUST PTHREAD_MUTEX_ROBUST
+#define DELAY_NSEC 0
+#define ROUNDS 1000
+#define N 32
+#include "tst-mutex7.c"