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

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Message-Id: <200806251538.45795.rusty@rustcorp.com.au>
Date:	Wed, 25 Jun 2008 15:38:45 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Mike Travis <travis@....com>
Cc:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Vegard Nossum <vegard.nossum@...il.com>,
	Adrian Bunk <bunk@...nel.org>,
	Srivatsa Vaddagiri <vatsa@...ibm.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 Wednesday 25 June 2008 00:44:45 Mike Travis wrote:
> Rusty Russell wrote:
> ...
>
> > Nice catch.  Basically, cpu_possible_map should only be cleared at boot,
> > and probably not even then.
>
> One thing that should be avoided, is clearing anything but the last bit in
> the cpu_possible_map.  This is because num_possible_cpus != nr_cpu_ids when
> there are holes in the map.  (nr_cpu_ids = highest possible cpu # + 1).

It's ok if nr_cpu_ids is an overestimate, isn't it?

But for this corner case, I think clearing cpu_possible_map is wrong.

Cheers,
Rusty.
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