Re: [PATCH 2/8] aio_poll_wake(): don't set ->woken if we ignore the wakeup

[zhengbin (A)]

So, what should we do?

On 2019/3/7 10:18, Al Viro wrote:
> On Thu, Mar 07, 2019 at 12:03:10AM +0000, Al Viro wrote:
>> From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
>>
>> In case of early wakeups, aio_poll() assumes that aio_poll_complete()
>> has either already happened or is imminent.  In that case we do not
>> want to put iocb on the list of cancellables.  However, ignored
>> wakeups need to be treated as if wakeup has not happened at all.
>> Trivially fixed by having aio_poll_wake() set ->woken only after
>> it's committed to taking iocb out of the waitqueue.
>>
>> Spotted-by: zhengbin <zhengbin13@xxxxxxxxxx>
>> Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> 
> ... and unfortunately it's worse than just that - what both of us
> have missed is that one could have non-specific wakep + schedule_work +
> aio_poll_complete_work() rechecking ->poll(), seeing nothing of
> interest and reinserting into queue.  All before vfs_poll() manages
> to return into aio_poll().  The window is harder to hit, but it's
> still there, with exact same "failed to add to cancel list" kind of bug
> if we do hit it ;-/
> 
> .
>