linux-kernel - Re: [git pull] scheduler fixes

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Date:	Sat, 31 Jan 2009 18:23:52 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Alexey Zaytsev <alexey.zaytsev@...il.com>
Subject: Re: [git pull] scheduler fixes

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.



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