Re: [PATCH RFC v4 12/15] io_uring/cmd: let cmds to know about dying task

[Bernd Schubert <bschubert@ddn.com>]

On 11/6/24 05:44, Ming Lei wrote:
> On Wed, Nov 6, 2024 at 7:02 AM Bernd Schubert <bschubert@ddn.com> wrote:
>>
>>
>>
>> On 11/5/24 02:08, Pavel Begunkov wrote:
>>>
>>> FWIW, the original version is how it's handled in several places
>>> across io_uring, and the difference is a gap for !DEFER_TASKRUN
>>> when a task_work is queued somewhere in between when a task is
>>> started going through exit() but haven't got PF_EXITING set yet.
>>> IOW, should be harder to hit.
>>>
>>
>> Does that mean that the test for PF_EXITING is racy and we cannot
>> entirely rely on it?
> 
> Another solution is to mark uring_cmd as io_uring_cmd_mark_cancelable(),
> which provides a chance to cancel cmd in the current context.

Yeah, I have that, see 
[PATCH RFC v4 14/15] fuse: {io-uring} Prevent mount point hang on fuse-server termination

As I just wrote to Pavel, getting IO_URING_F_TASK_DEAD is rather hard
in my current branch.IO_URING_F_CANCEL didn't make a difference ,
I had especially tried to disable it - still neither 
IO_URING_F_TASK_DEAD nor the crash got easily triggered. So I 
reenabled IO_URING_F_CANCEL and then eventually
got IO_URING_F_TASK_DEAD - i.e. without checking the underlying code,
looks like we need both for safety measures.


Thanks,
Bernd