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Subject: Re: lockdep trace from posix timers
From: Steven Rostedt <rostedt@goodmis.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>, Dave Jones <davej@redhat.com>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>, dhowells <dhowells@redhat.com>,
        Al Viro <viro@zeniv.linux.org.uk>
Date: Mon, 20 Aug 2012 08:19:01 -0400
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References: <20120724203613.GA9637@redhat.com>
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	 <1345463458.23018.37.camel@twins>
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On Mon, 2012-08-20 at 13:50 +0200, Peter Zijlstra wrote:
> On Mon, 2012-08-20 at 13:44 +0200, Peter Zijlstra wrote:
> >  int
> > +task_work_add(struct task_struct *task, struct callback_head *work, bool notify)
> >  {
> > +       struct callback_head **head = &task->task_works;
> > +       struct callback_head *entry, *old_entry;
> > +
> > +       entry = &head;
> 
> My compiler just alerted me that: 
> 
> 	entry = *head; 
> 
> works a lot better..
> 
> > +       for (;;) {
> > +               if (entry == &dead)

But your compiler likes "entry == &dead"? ;-)

-- Steve

> > +                       return -ESRCH;
> > +
> > +               old_entry = entry;
> > +               work->next = entry;
> > +               entry = cmpxchg(head, old_entry, work);
> > +               if (entry == old_entry)
> > +                       break;
> > +       }
> >  
> >         /* test_and_set_bit() implies mb(), see tracehook_notify_resume(). */
> >         if (notify)
> >                 set_notify_resume(task);
> > +
> >         return 0;
> >  }