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

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Message-ID: <a6f5f10b-b4f7-6674-79f0-31b14cfe3533@kernel.dk>
Date:   Fri, 26 Mar 2021 08:50:03 -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 8:43 AM, Stefan Metzmacher wrote:
> 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?

Usually yes, but this case is first doing SIGSTOP, so we're waiting in
get_signal() -> do_signal_stop() when the SIGKILL arrives. Hence there's
no way to catch it in the worker themselves.

-- 
Jens Axboe