On Tue, 10 Dec 2013, Dave Jones wrote:
> On Tue, Dec 10, 2013 at 11:55:06AM -0800, Linus Torvalds wrote:
> > On Tue, Dec 10, 2013 at 11:18 AM, Thomas Gleixner <t...@linutronix.de>
> wrote:
> > >
> > > So this is pretty unlikely. The retry requires:
> > >
> > > get_futex_value_locked() == EFAULT;
> > >
> > > Now we drop the hash bucket locks and do:
> > >
> > > get_user();
> > >
> > > And if that get_user() faults again, we bail out.
> >
> > I think you need to look closer.
> >
> > We have at least also that "futex_proxy_trylock_atomic() returns
> > -EAGAIN" case. Which triggers at some exit condition. Another thread
> > in the same group, perhaps never completing the exit because it's
> > waiting for this one? I dunno, I didn't look any closer (but this does
> > make me think "Hey, we should add Oleg to the Cc too", since
> > PF_EXITING is involved).. So maybe there is some situation where that
> > EAGAIN will keep happening, forever..
> >
> > Now, I'm *not* saying that that is it. It's quite possible/likely some
> > other loop, but I do have to say that it sure isn't _obvious_. And
> > that whole EAGAIN return case is quite deep and special, so ...
> >
> > Linus
> >
> > PS: Oleg - the whole thread is on lkml. Ping me if you need more context.
>
> btw, I've left the machine in that state, and will for as long as necesary
> in case someone has any ideas for further tracing experiments.
Can you gather a trace with the function tracer? That will tell us
what the thing is actually doing.
Thanks,
tglx
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