Re: [PATCH v3 07/22] kthread: Detect when a kthread work is used by more workers

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH v3 07/22] kthread: Detect when a kthread work is used by more workers
Date	2015-11-24 16:00 +0100
Message-ID	<qyney-130-7@gated-at.bofh.it> (permalink)
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On Tue, Nov 24, 2015 at 11:06:50AM +0100, Petr Mladek wrote:
> On Mon 2015-11-23 17:27:03, Tejun Heo wrote:
> > Hello,
> > 
> > On Wed, Nov 18, 2015 at 02:25:12PM +0100, Petr Mladek wrote:
> > > @@ -610,6 +625,12 @@ repeat:
> > >  	if (work) {
> > >  		__set_current_state(TASK_RUNNING);
> > >  		work->func(work);
> > > +
> > > +		spin_lock_irq(&worker->lock);
> > > +		/* Allow to queue the work into another worker */
> > > +		if (!kthread_work_pending(work))
> > > +			work->worker = NULL;
> > > +		spin_unlock_irq(&worker->lock);
> > 
> > Doesn't this mean that the work item can't be freed from its callback?
> > That pattern tends to happen regularly.
> 
> I am not sure if I understand your question. Do you mean switching
> work->func during the life time of the struct kthread_work? This
> should not be affected by the above code.

No, work->func(work) doing: kfree(work).

That is indeed something quite frequently done, and since you now have
references to work after calling func, things would go *boom* rather
quickly.
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[PATCH v3 07/22] kthread: Detect when a kthread work is used by more workers Petr Mladek <pmladek@suse.com> - 2015-11-18 14:30 +0100
  Re: [PATCH v3 07/22] kthread: Detect when a kthread work is used by  more workers Tejun Heo <tj@kernel.org> - 2015-11-23 23:30 +0100
    Re: [PATCH v3 07/22] kthread: Detect when a kthread work is used by  more workers Petr Mladek <pmladek@suse.com> - 2015-11-24 11:10 +0100
      Re: [PATCH v3 07/22] kthread: Detect when a kthread work is used by  more workers Tejun Heo <tj@kernel.org> - 2015-11-24 15:50 +0100
        Re: [PATCH v3 07/22] kthread: Detect when a kthread work is used by  more workers Petr Mladek <pmladek@suse.com> - 2015-11-24 17:30 +0100
      Re: [PATCH v3 07/22] kthread: Detect when a kthread work is used by  more workers Peter Zijlstra <peterz@infradead.org> - 2015-11-24 16:00 +0100

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