Author: davidxu
Date: Mon Nov 22 02:42:02 2010
New Revision: 215652
URL: http://svn.freebsd.org/changeset/base/215652
Log:
Use atomic instruction to set _has_writer, otherwise there is a race
causes userland to not wake up a thread sleeping in kernel.
MFC after: 3 days
Modified:
head/sys/kern/kern_umtx.c
Modified: head/sys/kern/kern_umtx.c
==============================================================================
--- head/sys/kern/kern_umtx.c Mon Nov 22 01:28:29 2010 (r215651)
+++ head/sys/kern/kern_umtx.c Mon Nov 22 02:42:02 2010 (r215652)
@@ -2839,7 +2839,8 @@ do_sem_wait(struct thread *td, struct _u
umtxq_insert(uq);
umtxq_unlock(&uq->uq_key);
- suword32(__DEVOLATILE(uint32_t *, &sem->_has_waiters), 1);
+ if (fuword32(__DEVOLATILE(uint32_t *, &sem->_has_waiters)) == 0)
+ casuword32(__DEVOLATILE(uint32_t *, &sem->_has_waiters), 0, 1);
count = fuword32(__DEVOLATILE(uint32_t *, &sem->_count));
if (count != 0) {
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