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

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Message-ID: <20200429191224.GA75562@google.com>
Date:   Wed, 29 Apr 2020 15:12:24 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Xiao Yang <yangx.jy@...fujitsu.com>, 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, Apr 29, 2020 at 12:31:41PM -0400, Steven Rostedt wrote:
> 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.

Agreed :-) thanks.

 - Joel