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Use atomic instruction to set _has_writer, otherwise there is a race

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causes userland to not wake up a thread sleeping in kernel.

MFC after: 3 days
This commit is contained in:
David Xu 2010-11-22 02:42:02 +00:00
parent e64ac239f6
commit b169d0efa1
1 changed files with 2 additions and 1 deletions
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3
sys/kern/kern_umtx.c
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@ -2839,7 +2839,8 @@ do_sem_wait(struct thread *td, struct _usem *sem, struct timespec *timeout)
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) {