Author: davidxu
Date: Tue Feb 9 01:19:10 2010
New Revision: 203694
URL: http://svn.freebsd.org/changeset/base/203694
Log:
MFC r203414:
After busied the lock, re-read state word before checking waiters flag,
otherwise, the waiters bit may not be set and a wakeup is lost.
Approved by: re (kib)
Modified:
stable/7/sys/kern/kern_umtx.c
Directory Properties:
stable/7/sys/ (props changed)
stable/7/sys/cddl/contrib/opensolaris/ (props changed)
stable/7/sys/contrib/dev/acpica/ (props changed)
stable/7/sys/contrib/pf/ (props changed)
Modified: stable/7/sys/kern/kern_umtx.c
==============================================================================
--- stable/7/sys/kern/kern_umtx.c Tue Feb 9 00:38:40 2010
(r203693)
+++ stable/7/sys/kern/kern_umtx.c Tue Feb 9 01:19:10 2010
(r203694)
@@ -2463,6 +2463,12 @@ do_rw_rdlock(struct thread *td, struct u
umtxq_busy(&uq->uq_key);
umtxq_unlock(&uq->uq_key);
+ /*
+ * re-read the state, in case it changed between the try-lock
above
+ * and the check below
+ */
+ state = fuword32(__DEVOLATILE(int32_t *, &rwlock->rw_state));
+
/* set read contention bit */
while ((state & wrflags) && !(state & URWLOCK_READ_WAITERS)) {
oldstate = casuword32(&rwlock->rw_state, state, state |
URWLOCK_READ_WAITERS);
@@ -2595,6 +2601,12 @@ do_rw_wrlock(struct thread *td, struct u
umtxq_busy(&uq->uq_key);
umtxq_unlock(&uq->uq_key);
+ /*
+ * re-read the state, in case it changed between the try-lock
above
+ * and the check below
+ */
+ state = fuword32(__DEVOLATILE(int32_t *, &rwlock->rw_state));
+
while (((state & URWLOCK_WRITE_OWNER) ||
URWLOCK_READER_COUNT(state) != 0) &&
(state & URWLOCK_WRITE_WAITERS) == 0) {
oldstate = casuword32(&rwlock->rw_state, state, state |
URWLOCK_WRITE_WAITERS);
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