On 7/19/21 11:28 AM, Pavel Begunkov wrote:

On 7/19/21 6:13 PM, Jens Axboe wrote:

quoted

On 7/19/21 10:57 AM, Pavel Begunkov wrote:

quoted

On 7/16/21 11:57 AM, syzbot wrote:

quoted

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING in io_uring_cancel_generic

__arm_poll doesn't remove a second poll entry in case of failed
__io_queue_proc(), it's most likely the cause here.

#syz test: https://github.com/isilence/linux.git syztest_sqpoll_hang

Was my thought on seeing the last debug run too. Haven't written a test
case, but my initial thought was catching this at the time that double
poll is armed, in __io_queue_proc(). Totally untested, just tossing
it out there.

Wouldn't help, unfortunately, the way syz triggers it is making a
request to go through __io_queue_proc() three times.

Either it's 3 waitqueues or we need to extend the check below to
the double poll entry.

if (poll_one->head == head)
	return;

Yes good point, that'd depend on single poll erroring first. Given
the variety of cases for it, catching it after the fact like in your
patch is likely the simplest/cleanest way.

-- 
Jens Axboe