File pthread-cond-broadcast-waiters-after-spinning.patch of Package glibc.14271
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.
Index: glibc-2.26/nptl/pthread_cond_common.c
===================================================================
--- glibc-2.26.orig/nptl/pthread_cond_common.c
+++ glibc-2.26/nptl/pthread_cond_common.c
@@ -405,8 +405,12 @@ __condvar_quiesce_and_switch_g1 (pthread
{
/* 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);