linux-kernel - Re: lockdep trace from posix timers

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Date:	Mon, 20 Aug 2012 17:10:34 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	rostedt <rostedt@...dmis.org>, dhowells <dhowells@...hat.com>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: lockdep trace from posix timers

On Mon, 2012-08-20 at 16:59 +0200, Oleg Nesterov wrote:
> On 08/20, Peter Zijlstra wrote:
> >
> >  task_work_cancel(struct task_struct *task, task_work_func_t func)
> >  {
> > ...
> > +
> > +again:
> > +	workp = &task->task_works;
> > +	work = *workp;
> > +	while (work) {
> > +		if (work->func == func) {
> 
> But this all can race with task_work_run() if task != current.
> 
> This "work" can be freed/reused. And it should only return !NULL
> if twork->func() was not called.

Ah, because we could be iterating the list after the xchg done by run.

Hmm.. 
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