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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Sun, 17 Feb 2013 09:32:15 -0800
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Subject: Re: Debugging Thinkpad T430s occasional suspend failure.
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>, Dave Jones <davej@redhat.com>,
        Hugh Dickins <hughd@google.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Paul McKenney <paul.mckenney@linaro.org>
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On Sun, Feb 17, 2013 at 7:11 AM, Frederic Weisbecker <fweisbec@gmail.com> wrote:
>
> preempt_value_in_interrupt() looks buggy in your patch: it makes
> invoke_softirq() returning if (val & HARDIRQ_MASK). But that's always
> true since you have moved further the sub_preempt_count(IRQ_EXIT)
> further.

No, that's not it. The value hasn't been written back yet, but it already did:

+       int offset = IRQ_EXIT_OFFSET;
+       int count = preempt_count() - offset;

so the 'count' has the IRQ_EXIT_OFFSET already subtracted. So no,
HARDIRQ_MASK is *not* always set.

                   Linus