Re: next-20090107: WARNING: at kernel/sched.c:4435sub_preempt_count

[Ingo Molnar]

* Alexey Zaytsev <alexey.zaytsev@xxxxxxxxx> wrote:

> Hi.
> 
> On Wed, Jan 14, 2009 at 05:00, Nick Piggin <npiggin@xxxxxxx> wrote:
> > On Sun, Jan 11, 2009 at 03:49:45AM +0100, Ingo Molnar wrote:
> >>
> >> * Alexey Zaytsev <alexey.zaytsev@xxxxxxxxx> wrote:
> >>
> >> > One more instance of http://marc.info/?l=linux-kernel&m=123134586202636&w=2
> >> > Added Ingo Molnar to CC.
> >>
> >> added Nick on Cc:. Nick, it's about:
> >>
> >> > commit 7317d7b87edb41a9135e30be1ec3f7ef817c53dd
> >> > Author: Nick Piggin <nickpiggin@xxxxxxxxxxxx>
> >> > Date:   Tue Sep 30 20:50:27 2008 +1000
> >> >
> >> >    sched: improve preempt debugging
> >>
> >> causing a seemingly spurious warning.
> >
> > I don't know how it is spurious... Presumably the sequence _would_ have
> > caused preempt count to go negative if the bkl were not held...
> >
> > __do_softirq does a __local_bh_disable on entry, and it seems like the
> > _local_bh_enable on exit is what causes this warning. So something is
> > unbalanced somehow. Or is it some weird thing we do in early boot that
> > I am missing?
> >
> > Can you put in some printks around these functions in early boot to
> > get an idea of what preempt_count is doing?
> 
> Sorry for the delay. I was busy and forgot about this issue.
> The warning does not show in -rc2 any more. Was it fixed, or
> just shadowed by something?

We reverted it in:

  01e3eb8: Revert "sched: improve preempt debugging"

We can apply a fixed version again if the failure mode is understood and 
fixed.

	Ingo
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