linux-kernel - Re: [PATCH v3] signal: break out of wait loops on kthread

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Date:   Mon, 11 Jul 2022 17:04:22 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] signal: break out of wait loops on kthread_stop()

"Jason A. Donenfeld" <Jason@...c4.com> writes:

> Hi Eric,
>
> Thanks for the review.
>
>> Which I guess my long way of saying I think you can just change
>> kthread_stop to say:
>> 
>> diff --git a/kernel/kthread.c b/kernel/kthread.c
>> index 544fd4097406..52e9b3432496 100644
>> --- a/kernel/kthread.c
>> +++ b/kernel/kthread.c
>> @@ -704,6 +704,7 @@ int kthread_stop(struct task_struct *k)
>>  	kthread = to_kthread(k);
>>  	set_bit(KTHREAD_SHOULD_STOP, &kthread->flags);
>>  	kthread_unpark(k);
>> +	set_tsk_thread_flag(k, TIF_NOTIFY_SIGNAL);
>>  	wake_up_process(k);
>>  	wait_for_completion(&kthread->exited);
>>  	ret = kthread->result;
>> 
>
> Okay. I'll constrain it to just kthread_stop(). But please file away in
> the back of your mind the potential for kthread_park() to be problematic
> down the line, in case we have to fix that later.

Definitely.  Right now I am certain you are motivated to test and make
certain the kthread_stop case will work.  I just have the feeling that
we don't care enough about kthread_park, and so attempting to solve it
now is as likely to cause problems as solve them.

Eric