linux-kernel - Re: [PATCH] Fix BUG: using smp_processor_id() in preemptible code in print_fatal

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Message-ID: <20090127030237.GA14108@redhat.com>
Date:	Tue, 27 Jan 2009 04:02:37 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ed Swierk <eswierk@...stanetworks.com>
Cc:	Ingo Molnar <mingo@...e.hu>, rml@...h9.net,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix BUG: using smp_processor_id() in preemptible code
	in print_fatal_signal()

On 01/26, Ed Swierk wrote:
>
> On Tue, 2009-01-27 at 01:41 +0100, Oleg Nesterov wrote:
> > Ed, Ingo, but isn't it better to just use raw_smp_processor_id() in
> > __show_regs() ? This is only debug info, the printed CPU doesn't
> > have the "exact" meaning.
>
> I guess it doesn't really matter which CPU the signal handling thread
> happened to be running on, but are there other situations where
> show_regs() is always expected to print the correct CPU (and if not, why
> bother printing the CPU at all)?  Disabling preemption here seems the
> safest approach and doesn't add much overhead.

OK.

> > And, without the comment, it is not easy to see why print_fatal_signal()
> > disables preeemption before show_regs().
>
> Agreed; here's an updated patch.

Actually, now I think show_regs() has other reasons to run with the
preemption disabled, __show_regs() does read_crX()/etc, I guess it is
better to stay on the same CPU throughout.

So, Ed, I am sorry for noise.

Oleg.

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