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SubjectRe: wait_on_page_bit_common(TASK_KILLABLE, EXCLUSIVE) can miss wakeup?
Excerpts from Oleg Nesterov's message of June 30, 2020 12:02 am:
> On 06/29, Nicholas Piggin wrote:
>>
>> prepare_to_wait_event() has a pretty good pattern (and comment), I would
>> favour using that (test the signal when inserting on the waitqueue).
>>
>> @@ -1133,6 +1133,15 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
>> for (;;) {
>> spin_lock_irq(&q->lock);
>>
>> + if (signal_pending_state(state, current)) {
>> + /* Must not lose an exclusive wake up, see
>> + * prepare_to_wait_event comment */
>> + list_del_init(&wait->entry);
>> + spin_unlock_irq(&q->lock);
>> + ret = -EINTR;
>
> Basically this is what my patch in the 1st email does. But note that we can't
> just set "ret = -EINTR" here, we will need to clear "ret" if test_and_set_bit()
> below succeeds. That is why I used another "int intr" variable.

You snipped off one more important line of context. No such games are
required AFAIKS.

Thanks,
Nick

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