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authorRich Felker <dalias@aerifal.cx>2020-10-26 15:56:25 -0400
committerRich Felker <dalias@aerifal.cx>2020-10-26 15:56:25 -0400
commit2d0bbe6c788938d1332609c014eeebc1dff966ac (patch)
tree6c673d0c6d5bb2dce4fbb9cb216101a482dc472f
parent0b87551bdfb74ac411caa335d8ad0b89a7f139c6 (diff)
downloadmusl-2d0bbe6c788938d1332609c014eeebc1dff966ac.tar.gz
fix pthread_cond_wait paired with with priority-inheritance mutex
pthread_cond_wait arranged for requeued waiters to wake when the mutex is unlocked by temporarily adjusting the mutex's waiter count. commit 54ca677983d47529bab8752315ac1a2b49888870 broke this when introducing PI mutexes by repurposing the waiter count field of the mutex structure. since then, for PI mutexes, the waiter count adjustment was misinterpreted by the mutex locking code as indicating that the mutex is non a non-recoverable state. it would be possible to special-case PI mutexes here, but instead just drop all adjustment of the waiters count, and instead use the lock word waiters bit for all mutex types. since the mutex is either held by the caller or in unrecoverable state at the time the bit is set, it will necessarily still be set at the time of any subsequent valid unlock operation, and this will produce the desired effect of waking the next waiter. if waiter counts are entirely dropped at some point in the future this code should still work without modification.
-rw-r--r--src/thread/pthread_cond_timedwait.c11
1 files changed, 5 insertions, 6 deletions
diff --git a/src/thread/pthread_cond_timedwait.c b/src/thread/pthread_cond_timedwait.c
index d1501240..f5f37af1 100644
--- a/src/thread/pthread_cond_timedwait.c
+++ b/src/thread/pthread_cond_timedwait.c
@@ -146,14 +146,13 @@ relock:
if (oldstate == WAITING) goto done;
- if (!node.next) a_inc(&m->_m_waiters);
-
/* Unlock the barrier that's holding back the next waiter, and
* either wake it or requeue it to the mutex. */
- if (node.prev)
- unlock_requeue(&node.prev->barrier, &m->_m_lock, m->_m_type & 128);
- else
- a_dec(&m->_m_waiters);
+ if (node.prev) {
+ int val = m->_m_lock;
+ if (val>0) a_cas(&m->_m_lock, val, val|0x80000000);
+ unlock_requeue(&node.prev->barrier, &m->_m_lock, m->_m_type & (8|128));
+ }
/* Since a signal was consumed, cancellation is not permitted. */
if (e == ECANCELED) e = 0;