linux-kernel - Re: current_thread_info() vs task_thread

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Date:	Tue, 19 Jul 2011 10:57:37 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Peter Zijlstra <peterz@...radead.org>, linux-arch@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: current_thread_info() vs task_thread_info(current)

On Mon, 2011-07-18 at 17:39 -0700, Paul E. McKenney wrote:
> > Hrm, no I don't see that happening no. The preempt count when
> exiting an
> > irq or softirq stack should be the exact same as when entering it,
> which
> > is why we don't bother copying it over. Do you see any case where
> that
> > wouldn't hold ?
> 
> Nope, other than seeing preempt_count() transition from zero to three
> across a spin_unlock_irqrestore() for no good reason that I could see.

Do you have a nice repro-case ? :-)

That sounds really nasty ... smells really like something bad's
happening from an interrupt, but we don't copy back the preempt-count
from the interrupt stacks at all, so that's really really odd.

Cheers,
Ben.


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