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SubjectRe: lockdep trace from posix timers
On Thu, Aug 16, 2012 at 08:54:31PM +0800, Ming Lei wrote:
> On Sat, Jul 28, 2012 at 12:20 AM, Dave Jones <davej@redhat.com> wrote:
> > On Tue, Jul 24, 2012 at 04:36:13PM -0400, Dave Jones wrote:
> > > Linus tree as of 5fecc9d8f59e765c2a48379dd7c6f5cf88c7d75a
> > >
> > > Dave
> > >
> > > ======================================================
> > > [ INFO: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected ]
> > > 3.5.0+ #122 Not tainted
> > > ------------------------------------------------------
> > > trinity-child2/5327 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
> > > blocked: (tasklist_lock){.+.+..}, instance: ffffffff81c05098, at: [<ffffffff8109762b>] posix_cpu_timer_del+0x2b/0xe0
> > >
> > > and this task is already holding:
> > > blocked: (&(&new_timer->it_lock)->rlock){-.-...}, instance: ffff880143bce170, at: [<ffffffff81093d49>] __lock_timer+0x89/0x1f0
> > > which would create a new lock dependency:
> > > (&(&new_timer->it_lock)->rlock){-.-...} -> (tasklist_lock){.+.+..}
> > >
> > > but this new dependency connects a HARDIRQ-irq-safe lock:
> > > (&(&new_timer->it_lock)->rlock){-.-...}
> > > ... which became HARDIRQ-irq-safe at:
> >
> > Shall I start bisecting this ? I can trigger it very easily, but if you
> > can give me a set of commits to narrow down, it'll speed up the bisection.
>
> It should a real possible deadlock, could you test the below patch to
> see if it can fix the warning?

I've not managed to hit it in a while. It seems very dependant upon
specific builds for some reason. Very strange.

Dave


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