linux-kernel - Re: v2.6.26-rc7: BUG: unable to handle kernel NULL pointer dereference

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Message-Id: <200806231326.11328.rusty@rustcorp.com.au>
Date:	Mon, 23 Jun 2008 13:26:10 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	"Vegard Nossum" <vegard.nossum@...il.com>
Cc:	"Adrian Bunk" <bunk@...nel.org>,
	"Srivatsa Vaddagiri" <vatsa@...ibm.com>,
	"Mike Travis" <travis@....com>, linux-kernel@...r.kernel.org,
	"Gautham R Shenoy" <ego@...ibm.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"Zhang, Yanmin" <yanmin.zhang@...el.com>,
	"Heiko Carstens" <heiko.carstens@...ibm.com>
Subject: Re: v2.6.26-rc7: BUG: unable to handle kernel NULL pointer dereference

On Monday 23 June 2008 02:29:07 Vegard Nossum wrote:
> And the (cpu < nr_cpu_ids) fails because the CPU has just been
> offlined (or failed to initialize, but it's the same thing), while
> NR_CPUS is the value that was compiled in as CONFIG_NR_CPUS (so the
> former check will always be true).
>
> I don't think it is valid to ask for a per_cpu() variable on a CPU
> which does not exist, though

Yes it is.  As long as cpu_possible(cpu), per_cpu(cpu) is valid.

The number check should be removed: checking cpu_possible() is sufficient.

Hope that helps,
Rusty.
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