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

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Message-ID: <20090127004124.GA10632@redhat.com>
Date:	Tue, 27 Jan 2009 01:41:24 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Ed Swierk <eswierk@...stanetworks.com>, 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 01/27, Ingo Molnar wrote:
>
> * Ed Swierk <eswierk@...stanetworks.com> wrote:
>
> > Take 2:
> >
> > With print-fatal-signals=1 on a kernel with CONFIG_PREEMPT=y, sending an
> > unexpected signal to a process causes a BUG: using smp_processor_id() in
> > preemptible code.
> >
> > get_signal_to_deliver() releases the siglock before calling
> > print_fatal_signal(), which calls show_regs(), which calls
> > smp_processor_id(), which is not supposed to be called from a
> > preemptible thread.
> >
> > Signed-off-by: Ed Swierk <eswierk@...stanetworks.com>
>
> applied to tip/core/urgent, thanks Ed!

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.

And, without the comment, it is not easy to see why print_fatal_signal()
disables preeemption before show_regs().

Oleg.

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