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Date: Thu, 3 Feb 2011 18:17:39 +0800
From: Yong Zhang <yong.zhang0@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Nick Bowler <nbowler@elliptictech.com>, linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: Regression: WARNINGS and lockdep spews in 2.6.38-rc3+
 (bisected).
Message-ID: <20110203101739.GA1551@zhy>
Reply-To: Yong Zhang <yong.zhang0@gmail.com>
References: <20110203031943.GA8910@elliptictech.com>
 <20110203091227.GA1603@zhy>
 <1296725440.26581.354.camel@laptop>
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On Thu, Feb 03, 2011 at 10:30:40AM +0100, Peter Zijlstra wrote:
> On Thu, 2011-02-03 at 17:12 +0800, Yong Zhang wrote:
> >  #ifdef CONFIG_LOCKDEP
> > +       unsigned long flags;
> > +
> >         local_bh_disable();
> >         lock_map_acquire(&timer->lockdep_map);
> >         lock_map_release(&timer->lockdep_map);
> > -       local_bh_enable();
> > +       /* raw_local_irq_[save|restore] is to protect _local_bh_enable() */
> > +       raw_local_irq_save(flags);
> > +       _local_bh_enable();
> > +       raw_local_irq_restore(flags);
> >  #endif 
> 
> _why_ are you doing the raw_local_irq stuff? That's just weird, and that
> comment isn't helping.

Just to avoid trigger WARN_ON_ONCE(!irqs_disabled()) in __local_bh_enable(),

> 
> Also, calling _local_bh_enable() will leave pending softirqs, not
> particularly nice

Ah, indeed. That's bad.

Now I'm not sure how to work around this issue, because local_bh_enable()
and _local_bh_enable() are not suitable here.

Maybe we can introduce another type of local_bh_enable() in which
waking up ksoftirqd is forced if needed.

Thanks,
Yong
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