Re: v2.6.26-rc7: BUG: unable to handle kernel NULL pointer dereference
- From: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
- Date: Tue, 24 Jun 2008 11:36:51 +1000
On Tuesday 24 June 2008 02:58:44 Mike Travis wrote:
Rusty Russell wrote:
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.
I don't see a check for index being out of range in cpu_possible().
You're right. It assumes cpu is < NR_CPUS. Hmm, I have no idea what's going
on. nr_cpu_ids (ignore that it's a horrible name for a bad idea) should be
fine to test against.
Vegard's analysis is flawed: just because cpu is offline, it still must be <
nr_cpu_ids, which is based on possible cpus. Unless something crazy is
happening, but a quick grep doesn't reveal anyone manipulating nr_cpu_ids.
If changing this fixes the bug, something else is badly wrong...
Rusty.
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