Re: [PATCH] fix exit_itimers() vs posix_timer_event() AB-BAdeadlock

[Oleg Nesterov <oleg@tv-sign.ru>]

Oleg Nesterov wrote:
> 
> Andrew Morton wrote:
> >
> > Oleg Nesterov <oleg@tv-sign.ru> wrote:
> > >
> > > +     /*
> > >  +     * We are locking ->it_lock + tasklist_lock backwards
> > >  +     * from release_task()->exit_itimers(), beware deadlock.
> > >  +     */
> > >  +    leader = timr->it_process->group_leader;
> > >  +    while (unlikely(!read_trylock(&tasklist_lock))) {
> > >  +            if (leader->flags & PF_EXITING) {
> > >  +                    smp_rmb();
> > >  +                    if (thread_group_empty(leader))
> > >  +                            return 0;
> > >  +            }
> > >  +            cpu_relax();
> > >  +    }
> >
> > Oh dear.  Is there no way to fix this up by taking the locks in the correct
> > order?  (Whatever that is).

Andrew, please drop this patch. It is obsoleted by Roland's
"[PATCH] Call exit_itimers from do_exit, not __exit_signal".

Oleg.