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From: Jens Axboe <[email protected]>
To: Stefan Metzmacher <[email protected]>, [email protected]
Cc: [email protected], [email protected],
	[email protected], [email protected]
Subject: Re: [PATCH 0/6] Allow signals for IO threads
Date: Fri, 26 Mar 2021 09:10:05 -0600	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On 3/26/21 9:08 AM, Stefan Metzmacher wrote:
> Am 26.03.21 um 15:55 schrieb Jens Axboe:
>> On 3/26/21 8:53 AM, Jens Axboe wrote:
>>> 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.
>>
>> Can you try this? Not crazy about adding a special case, but I don't
>> think there's any way around this one. And should be pretty cheap, as
>> we're already pulling in ->flags right above anyway.
>>
>> diff --git a/kernel/signal.c b/kernel/signal.c
>> index 5ad8566534e7..5b75fbe3d2d6 100644
>> --- a/kernel/signal.c
>> +++ b/kernel/signal.c
>> @@ -2752,6 +2752,15 @@ bool get_signal(struct ksignal *ksig)
>>  		 */
>>  		current->flags |= PF_SIGNALED;
>>  
>> +		/*
>> +		 * PF_IO_WORKER threads will catch and exit on fatal signals
>> +		 * themselves. They have cleanup that must be performed, so
>> +		 * we cannot call do_exit() on their behalf. coredumps also
>> +		 * do not apply to them.
>> +		 */
>> +		if (current->flags & PF_IO_WORKER)
>> +			return false;
>> +
>>  		if (sig_kernel_coredump(signr)) {
>>  			if (print_fatal_signals)
>>  				print_fatal_signal(ksig->info.si_signo);
>>
> 
> I guess not before next week, but if it resolves the problem for you,
> I guess it would be good to get this into rc5.

It does, I pushed out a new branch. I'll send out a v2 series in a bit.

-- 
Jens Axboe


  reply	other threads:[~2021-03-26 15:10 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-26  0:39 [PATCH 0/6] Allow signals for IO threads Jens Axboe
2021-03-26  0:39 ` [PATCH 1/8] io_uring: handle signals for IO threads like a normal thread Jens Axboe
2021-03-26  0:39 ` [PATCH 2/8] kernel: unmask SIGSTOP for IO threads Jens Axboe
2021-03-26 13:48   ` Oleg Nesterov
2021-03-26 15:01     ` Jens Axboe
2021-03-26 15:23       ` Stefan Metzmacher
2021-03-26 15:29         ` Jens Axboe
2021-03-26 18:01           ` Stefan Metzmacher
2021-03-26 18:59             ` Jens Axboe
2021-04-01 14:53             ` Stefan Metzmacher
2021-03-26  0:39 ` [PATCH 3/8] Revert "signal: don't allow sending any signals to PF_IO_WORKER threads" Jens Axboe
2021-03-26  0:39 ` [PATCH 4/8] Revert "kernel: treat PF_IO_WORKER like PF_KTHREAD for ptrace/signals" Jens Axboe
2021-03-26  0:39 ` [PATCH 5/8] Revert "kernel: freezer should treat PF_IO_WORKER like PF_KTHREAD for freezing" Jens Axboe
2021-03-26  0:39 ` [PATCH 6/8] Revert "signal: don't allow STOP on PF_IO_WORKER threads" Jens Axboe
     [not found] ` <[email protected]>
2021-03-26 12:56   ` [PATCH 0/6] Allow signals for IO threads Jens Axboe
2021-03-26 13:31     ` Stefan Metzmacher
2021-03-26 13:54       ` Jens Axboe
2021-03-26 13:59         ` Jens Axboe
2021-03-26 14:38           ` Jens Axboe
2021-03-26 14:43             ` Stefan Metzmacher
2021-03-26 14:45               ` Stefan Metzmacher
2021-03-26 14:53                 ` Jens Axboe
2021-03-26 14:55                   ` Jens Axboe
2021-03-26 15:08                     ` Stefan Metzmacher
2021-03-26 15:10                       ` Jens Axboe [this message]
2021-03-26 15:11                         ` Stefan Metzmacher
2021-03-26 15:12                           ` Jens Axboe
2021-03-26 15:04                   ` Stefan Metzmacher
2021-03-26 15:09                     ` Jens Axboe
2021-03-26 14:50               ` Jens Axboe
2021-03-27  1:46       ` Stefan Metzmacher
2021-03-27 16:41         ` Jens Axboe
2021-04-01 14:58         ` Stefan Metzmacher
2021-04-01 15:39           ` Linus Torvalds
2021-04-01 16:00             ` Stefan Metzmacher
2021-04-01 16:24               ` Linus Torvalds
2021-04-03  0:48                 ` Stefan Metzmacher

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