diff options
| -rw-r--r-- | kern/thread.c | 19 |
1 files changed, 6 insertions, 13 deletions
diff --git a/kern/thread.c b/kern/thread.c index 2d51d13d..d08ce9d6 100644 --- a/kern/thread.c +++ b/kern/thread.c @@ -383,23 +383,16 @@ thread_runq_wakeup(struct thread_runq *runq, struct thread *thread) thread->state = THREAD_RUNNING; thread_runq_add(runq, thread); - if (runq != thread_runq_local()) { + if ((runq != thread_runq_local()) + && thread_test_flag(runq->current, THREAD_RESCHEDULE)) { /* - * Make the new state and flags globally visible so that a remote - * rescheduling operation sees the correct values. - * - * Although scheduling implies a load memory barrier before testing - * the state of a thread (because of the spin lock acquire semantics), - * this isn't the case with thread flags. They are set atomically, - * but not ordered. As a result, reenabling preemption may miss a - * rescheduling request. But interrupts imply full memory barriers - * so the request won't be missed when the rescheduling IPI is - * received by the remote processor. + * Make the new flags globally visible before sending the + * rescheduling request. This barrier pairs with the one implied + * by the rescheduling IPI. */ mb_store(); - if (thread_test_flag(runq->current, THREAD_RESCHEDULE)) - tcb_send_reschedule(thread_runq_id(runq)); + tcb_send_reschedule(thread_runq_id(runq)); } } |