From: Rusty Russell <rusty@rustcorp.com.au>
To: "Vegard Nossum" <vegard.nossum@gmail.com>
Subject: Re: v2.6.26-rc7: BUG: unable to handle kernel NULL pointer dereference
Date: Mon, 23 Jun 2008 13:26:10 +1000
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Cc: "Adrian Bunk" <bunk@kernel.org>, "Srivatsa Vaddagiri" <vatsa@in.ibm.com>,
       "Mike Travis" <travis@sgi.com>, linux-kernel@vger.kernel.org,
       "Gautham R Shenoy" <ego@in.ibm.com>, "Rafael J. Wysocki" <rjw@sisk.pl>,
       "Zhang, Yanmin" <yanmin.zhang@intel.com>,
       "Heiko Carstens" <heiko.carstens@de.ibm.com>
References: <20080622125633.GA8166@damson.getinternet.no> <20080622155627.GA20122@cs181140183.pp.htv.fi> <19f34abd0806220929y1ca9d0c4nbf480473b7ce018a@mail.gmail.com>
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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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