linux-kernel - Re: [PATCH 0/6] Allow signals for IO threads

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Date:   Fri, 26 Mar 2021 08:53:07 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Stefan Metzmacher <metze@...ba.org>, io-uring@...r.kernel.org
Cc:     torvalds@...ux-foundation.org, ebiederm@...ssion.com,
        oleg@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/6] Allow signals for IO threads

On 3/26/21 8:45 AM, Stefan Metzmacher wrote:
> Am 26.03.21 um 15:43 schrieb Stefan Metzmacher:
>> Am 26.03.21 um 15:38 schrieb Jens Axboe:
>>> On 3/26/21 7:59 AM, Jens Axboe wrote:
>>>> On 3/26/21 7:54 AM, Jens Axboe wrote:
>>>>>> The KILL after STOP deadlock still exists.
>>>>>
>>>>> In which tree? Sounds like you're still on the old one with that
>>>>> incremental you sent, which wasn't complete.
>>>>>
>>>>>> Does io_wq_manager() exits without cleaning up on SIGKILL?
>>>>>
>>>>> No, it should kill up in all cases. I'll try your stop + kill, I just
>>>>> tested both of them separately and didn't observe anything. I also ran
>>>>> your io_uring-cp example (and found a bug in the example, fixed and
>>>>> pushed), fwiw.
>>>>
>>>> I can reproduce this one! I'll take a closer look.
>>>
>>> OK, that one is actually pretty straight forward - we rely on cleaning
>>> up on exit, but for fatal cases, get_signal() will call do_exit() for us
>>> and never return. So we might need a special case in there to deal with
>>> that, or some other way of ensuring that fatal signal gets processed
>>> correctly for IO threads.
>>
>> And if (fatal_signal_pending(current)) doesn't prevent get_signal() from being called?
> 
> Ah, we're still in the first get_signal() from SIGSTOP, correct?

Yes exactly, we're waiting in there being stopped. So we either need to
check to something ala:

relock:
+	if (current->flags & PF_IO_WORKER && fatal_signal_pending(current))
+		return false;

to catch it upfront and from the relock case, or add:

	fatal:
+		if (current->flags & PF_IO_WORKER)
+			return false;

to catch it in the fatal section.

-- 
Jens Axboe