pthread_cond_broadcast: Fix waiters-after-spinning case [BZ #23538]

diff --git a/ChangeLog b/ChangeLog
index f97c55108a85c0439d4a68f7202a33cdc54453c6..9fc0060be2ac26e12204894106dce11d44198d27 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2018-08-27 Martin Kuchta  <martin.kuchta@netapp.com>
+          Torvald Riegel  <triegel@redhat.com>
+
+       [BZ #23538]
+       * nptl/pthread_cond_common.c (__condvar_quiesce_and_switch_g1):
+       Update r to include the set wake-request flag if waiters are
+       remaining after spinning.
+
 2018-08-27  Joseph Myers  <joseph@codesourcery.com>
 
        * sysdeps/gnu/netinet/udp.h (UDP_SEGMENT): New macro.

diff --git a/nptl/pthread_cond_common.c b/nptl/pthread_cond_common.c
index 8e425eb01eceabec64e2bad3cfeb2ec51b6f6d72..479e54febb41767596c85c3312716b6c52c8700a 100644 (file)
--- a/nptl/pthread_cond_common.c
+++ b/nptl/pthread_cond_common.c
@@ -405,8 +405,12 @@ __condvar_quiesce_and_switch_g1 (pthread_cond_t *cond, uint64_t wseq,
        {
          /* There is still a waiter after spinning.  Set the wake-request
             flag and block.  Relaxed MO is fine because this is just about
-            this futex word.  */
-         r = atomic_fetch_or_relaxed (cond->__data.__g_refs + g1, 1);
+            this futex word.
+
+            Update r to include the set wake-request flag so that the upcoming
+            futex_wait only blocks if the flag is still set (otherwise, we'd
+            violate the basic client-side futex protocol).  */
+         r = atomic_fetch_or_relaxed (cond->__data.__g_refs + g1, 1) | 1;
 
          if ((r >> 1) > 0)
            futex_wait_simple (cond->__data.__g_refs + g1, r, private);