On 09/06, Oleg Nesterov wrote:
>
> + if (unlikely(signal_pending_state(state, current))) {
> + /*
> + * Exclusive waiter must not fail if it was selected by wakeup,
> + * it should "consume" the condition we were waiting for.
> + *
> + * The caller will recheck the condition and return success if
> + * we were already woken up, we can not miss the event because
> + * wakeup locks/unlocks the same q->lock.
> + *
> + * But we need to ensure that set-condition + wakeup after that
> + * can't see us, it should wake up another exclusive waiter if
> + * we fail.
> + */
> + list_del_init(&wait->task_list);
> + ret = -ERESTARTSYS;
Yes, but we should not do set_current_state() in this case, please sere V3.
-------------------------------------------------------------------------------
Subject: [PATCH V3 2/4] sched/wait: avoid abort_exclusive_wait() in
___wait_event()
___wait_event() doesn't really need abort_exclusive_wait(), we can simply
change prepare_to_wait_event() to remove the waiter from q->task_list if
it was interrupted.
This simplifies the code/logic, and this way prepare_to_wait_event() can
have more users, see the next change.
Signed-off-by: Oleg Nesterov <o...@redhat.com>
---
include/linux/wait.h | 7 +------
kernel/sched/wait.c | 35 +++++++++++++++++++++++++----------
2 files changed, 26 insertions(+), 16 deletions(-)
diff --git a/include/linux/wait.h b/include/linux/wait.h
index 329f796..5179915 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -280,12 +280,7 @@ wait_queue_head_t *bit_waitqueue(void *, int);
\
if (___wait_is_interruptible(state) && __int) { \
__ret = __int; \
- if (exclusive) { \
- abort_exclusive_wait(&wq, &__wait, \
- NULL); \
- goto __out; \
- } \
- break; \
+ goto __out; \
} \
\
cmd; \
diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c
index 2bbba01..2612393 100644
--- a/kernel/sched/wait.c
+++ b/kernel/sched/wait.c
@@ -199,24 +199,39 @@ EXPORT_SYMBOL(prepare_to_wait_exclusive);
long prepare_to_wait_event(wait_queue_head_t *q, wait_queue_t *wait, int state)
{
unsigned long flags;
-
- if (signal_pending_state(state, current))
- return -ERESTARTSYS;
+ long ret = 0;
wait->private = current;
wait->func = autoremove_wake_function;
spin_lock_irqsave(&q->lock, flags);
- if (list_empty(&wait->task_list)) {
- if (wait->flags & WQ_FLAG_EXCLUSIVE)
- __add_wait_queue_tail(q, wait);
- else
- __add_wait_queue(q, wait);
+ if (unlikely(signal_pending_state(state, current))) {
+ /*
+ * Exclusive waiter must not fail if it was selected by wakeup,
+ * it should "consume" the condition we were waiting for.
+ *
+ * The caller will recheck the condition and return success if
+ * we were already woken up, we can not miss the event because
+ * wakeup locks/unlocks the same q->lock.
+ *
+ * But we need to ensure that set-condition + wakeup after that
+ * can't see us, it should wake up another exclusive waiter if
+ * we fail.
+ */
+ list_del_init(&wait->task_list);
+ ret = -ERESTARTSYS;
+ } else {
+ if (list_empty(&wait->task_list)) {
+ if (wait->flags & WQ_FLAG_EXCLUSIVE)
+ __add_wait_queue_tail(q, wait);
+ else
+ __add_wait_queue(q, wait);
+ }
+ set_current_state(state);
}
- set_current_state(state);
spin_unlock_irqrestore(&q->lock, flags);
- return 0;
+ return ret;
}
EXPORT_SYMBOL(prepare_to_wait_event);
--
2.5.0
