linux-kernel - Re: [PATCH] kernel/trace: Stop and wait for kthread on preempt irq module unload

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Message-ID: <20200429123141.580f89ce@gandalf.local.home>
Date:   Wed, 29 Apr 2020 12:31:41 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Xiao Yang <yangx.jy@...fujitsu.com>
Cc:     "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] kernel/trace: Stop and wait for kthread on preempt irq
 module unload

On Wed, 29 Apr 2020 19:54:16 +0800
Xiao Yang <yangx.jy@...fujitsu.com> wrote:

> On 2020/4/28 22:45, Steven Rostedt wrote:
> > diff --git a/kernel/trace/preemptirq_delay_test.c b/kernel/trace/preemptirq_delay_test.c  
> >>  index 1c28ca20e30b..6d9131ae7e8c 100644
> >>  --- a/kernel/trace/preemptirq_delay_test.c
> >>  +++ b/kernel/trace/preemptirq_delay_test.c
> >>  @@ -113,15 +113,27 @@ static int preemptirq_delay_run(void *data)
> >>
> >>    	for (i = 0; i<  s; i++)
> >>    		(testfuncs[i])(i);
> >>  +
> >>  +	while (!kthread_should_stop()) {
> >>  +		schedule();
> >>  +		set_current_state(TASK_INTERRUPTIBLE);
> >>  +	}
> >>  +
> >>  +	__set_current_state(TASK_RUNNING);
> >>  +
> >>    	return 0;
> >>    }
> >>  
> Hi Steven,
> 
> Thanks for your patch.
> 
> I also used the following steps to do test and didn't get any 
> warning/panic after applying your patch.
> ---------------------------------
> for i in $(seq 1 100); do modprobe preemptirq_delay_test test_mode=irq 
> delay=500000; rmmod preemptirq_delay_test; done
> for i in $(seq 1 100); do modprobe preemptirq_delay_test 
> test_mode=preempt delay=500000; rmmod preemptirq_delay_test; done
> ---------------------------------
> 
> But I am not sure which fix(from you and Joel) is better.

Mine ;-)

The "kthread_should_stop()" is the normal way to end kernel threads. Using
get/put is not the orthodox way.

-- Steve