57 lines
2.2 KiB
Diff
57 lines
2.2 KiB
Diff
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From 2d0bbe6c788938d1332609c014eeebc1dff966ac Mon Sep 17 00:00:00 2001
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From: Rich Felker <dalias@aerifal.cx>
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Date: Mon, 26 Oct 2020 15:56:25 -0400
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Subject: fix pthread_cond_wait paired with with priority-inheritance mutex
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pthread_cond_wait arranged for requeued waiters to wake when the mutex
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is unlocked by temporarily adjusting the mutex's waiter count. commit
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54ca677983d47529bab8752315ac1a2b49888870 broke this when introducing
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PI mutexes by repurposing the waiter count field of the mutex
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structure. since then, for PI mutexes, the waiter count adjustment was
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misinterpreted by the mutex locking code as indicating that the mutex
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is non a non-recoverable state.
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it would be possible to special-case PI mutexes here, but instead just
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drop all adjustment of the waiters count, and instead use the lock
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word waiters bit for all mutex types. since the mutex is either held
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by the caller or in unrecoverable state at the time the bit is set, it
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will necessarily still be set at the time of any subsequent valid
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unlock operation, and this will produce the desired effect of waking
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the next waiter.
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if waiter counts are entirely dropped at some point in the future this
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code should still work without modification.
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---
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src/thread/pthread_cond_timedwait.c | 11 +++++------
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1 file changed, 5 insertions(+), 6 deletions(-)
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(limited to 'src/thread/pthread_cond_timedwait.c')
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diff --git a/src/thread/pthread_cond_timedwait.c b/src/thread/pthread_cond_timedwait.c
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index d1501240..f5f37af1 100644
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--- a/src/thread/pthread_cond_timedwait.c
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+++ b/src/thread/pthread_cond_timedwait.c
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@@ -146,14 +146,13 @@ relock:
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if (oldstate == WAITING) goto done;
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- if (!node.next) a_inc(&m->_m_waiters);
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-
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/* Unlock the barrier that's holding back the next waiter, and
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* either wake it or requeue it to the mutex. */
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- if (node.prev)
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- unlock_requeue(&node.prev->barrier, &m->_m_lock, m->_m_type & 128);
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- else
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- a_dec(&m->_m_waiters);
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+ if (node.prev) {
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+ int val = m->_m_lock;
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+ if (val>0) a_cas(&m->_m_lock, val, val|0x80000000);
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+ unlock_requeue(&node.prev->barrier, &m->_m_lock, m->_m_type & (8|128));
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+ }
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/* Since a signal was consumed, cancellation is not permitted. */
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if (e == ECANCELED) e = 0;
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--
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