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Subject: Re: [git pull] scheduler fixes
From: Peter Zijlstra <peterz@infradead.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
       linux-kernel@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
       Nick Piggin <npiggin@suse.de>,
       Alexey Zaytsev <alexey.zaytsev@gmail.com>
In-Reply-To: <1233421901.4787.27.camel@laptop>
References: <20090130230936.GA7549@elte.hu>
	 <1233421901.4787.27.camel@laptop>
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Date: Sat, 31 Jan 2009 18:23:52 +0100
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On Sat, 2009-01-31 at 18:11 +0100, Peter Zijlstra wrote:
> > diff --git a/kernel/sched.c b/kernel/sched.c
> > index 52bbf1c..5686bb5 100644
> > --- a/kernel/sched.c
> > +++ b/kernel/sched.c
> > @@ -4440,7 +4450,7 @@ void __kprobes sub_preempt_count(int val)
> >       /*
> >        * Underflow?
> >        */
> > -     if (DEBUG_LOCKS_WARN_ON(val > preempt_count()))
> > +       if (DEBUG_LOCKS_WARN_ON(val > preempt_count() - (!!kernel_locked())))
> >               return;
> >       /*
> >        * Is the spinlock portion underflowing?

Since the commit msg of 01e3eb8 says:

    kernel_locked() is not a valid test in IRQ context (we update the
    BKL's ->lock_depth and the preempt count separately and non-atomicalyy),
    so we cannot put it into the generic preempt debugging checks which
    can run in IRQ contexts too.

Another possibility would be writing it like:

  if (DEBUG_LOCKS_WARN_ON(val > preempt_count() -
			  (in_interrupt() ? 0 : !!kernel_locked())))

Which might just work because we're in sub_preempt_count, before we
actually do the subtraction, so in_interrupt() will still be true.