Re: lockdep trace from posix timers

[Peter Zijlstra]

On Mon, 2012-08-20 at 17:10 +0200, Peter Zijlstra wrote:
> 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.

I guess we could steal the entire list and requeue it afterwards and
lift TIF_NOTIFY_RESUME along with it.. but I can't say that's pretty.




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