From 99ea93ca31795469d2a1f1570f17a5c39c2eb7e2 Mon Sep 17 00:00:00 2001 From: Martin Kuchta Date: Mon, 27 Aug 2018 17:03:35 +0200 Subject: [PATCH] pthread_cond_broadcast: Fix waiters-after-spinning case [BZ #23538] --- ChangeLog | 8 ++++++++ nptl/pthread_cond_common.c | 8 ++++++-- 2 files changed, 14 insertions(+), 2 deletions(-) diff --git a/ChangeLog b/ChangeLog index f97c55108a..9fc0060be2 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,11 @@ +2018-08-27 Martin Kuchta + Torvald Riegel + + [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 * sysdeps/gnu/netinet/udp.h (UDP_SEGMENT): New macro. diff --git a/nptl/pthread_cond_common.c b/nptl/pthread_cond_common.c index 8e425eb01e..479e54febb 100644 --- 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);