28 lines
1.2 KiB
Diff
28 lines
1.2 KiB
Diff
commit aa8a3e4cdef20c50cb20f008864fff05cbfbdf29
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Author: Martin Kuchta <martin.kuchta@netapp.com>
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Date: Mon Aug 27 18:54:46 2018 +0200
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pthread_cond_broadcast: Fix waiters-after-spinning case [BZ #23538]
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(cherry picked from commit 99ea93ca31795469d2a1f1570f17a5c39c2eb7e2)
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diff --git a/nptl/pthread_cond_common.c b/nptl/pthread_cond_common.c
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index 8e425eb01eceabec..479e54febb417675 100644
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--- a/nptl/pthread_cond_common.c
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+++ b/nptl/pthread_cond_common.c
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@@ -405,8 +405,12 @@ __condvar_quiesce_and_switch_g1 (pthread_cond_t *cond, uint64_t wseq,
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{
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/* There is still a waiter after spinning. Set the wake-request
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flag and block. Relaxed MO is fine because this is just about
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- this futex word. */
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- r = atomic_fetch_or_relaxed (cond->__data.__g_refs + g1, 1);
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+ this futex word.
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+
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+ Update r to include the set wake-request flag so that the upcoming
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+ futex_wait only blocks if the flag is still set (otherwise, we'd
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+ violate the basic client-side futex protocol). */
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+ r = atomic_fetch_or_relaxed (cond->__data.__g_refs + g1, 1) | 1;
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if ((r >> 1) > 0)
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futex_wait_simple (cond->__data.__g_refs + g1, r, private);
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