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

(cherry picked from commit 99ea93ca31795469d2a1f1570f17a5c39c2eb7e2)

diff --git a/ChangeLog b/ChangeLog
index 7e22bd1dfcd95e96276bc9d5be850172d1fdb6b9..2b771ca994565563d5bd478df12ed10ab3cb22bc 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.
+
 2018-07-29  H.J. Lu  <hongjiu.lu@intel.com>
 
        [BZ #23459]

diff --git a/NEWS b/NEWS
index 61ac02cd691fefe659b1e96ac48212b309a43aa9..a868a652f71ae10224ca0901b42a773e8c24377e 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -146,6 +146,7 @@ The following bugs are resolved with this release:
   [23236] Harden function pointers in _IO_str_fields
   [23313] libio: Disable vtable validation in case of interposition
   [23349] Various glibc headers no longer compatible with <linux/time.h>
+  [23538] pthread_cond_broadcast: Fix waiters-after-spinning case
   [23363] stdio-common/tst-printf.c has non-free license
   [23456] Wrong index_cpu_LZCNT
   [23459] COMMON_CPUID_INDEX_80000001 isn't populated for Intel processors

diff --git a/nptl/pthread_cond_common.c b/nptl/pthread_cond_common.c
index ffbbde4106e60db21fca41b31c255cff56ec5ea1..c99435e439747460e730d356a621931648e50ed7 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);