linux-kernel - Re: [PATCH] powerpc: on crash, kexec'ed kernel needs all CPUs are online

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Date:	Fri, 16 Oct 2015 13:14:50 +1100
From:	Michael Ellerman <mpe@...erman.id.au>
To:	Laurent Vivier <lvivier@...hat.com>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	dgibson@...hat.com, thuth@...hat.com
Subject: Re: [PATCH] powerpc: on crash, kexec'ed kernel needs all CPUs are
 online

On Thu, 2015-10-15 at 21:00 +0200, Laurent Vivier wrote:
> On kexec, all secondary offline CPUs are onlined before
> starting the new kernel, this is not done in the case of kdump.
> 
> If kdump is configured and a kernel crash occurs whereas
> some secondaries CPUs are offline (SMT=off),
> the new kernel is not able to start them and displays some
> "Processor X is stuck.".

Do we know why they are stuck?

I really don't like this fix. The reason we're doing a kdump is because the
first kernel has panicked, possibly with locks held or data structures
corrupted. Calling cpu_up() then goes and tries to run a bunch of code in the
crashed kernel, which increases the chance of us just wedging completely.

cheers


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