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

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Message-ID: <20151105123243.47dda843@voom.fritz.box>
Date:	Thu, 5 Nov 2015 12:32:43 +1100
From:	David Gibson <dgibson@...hat.com>
To:	Laurent Vivier <lvivier@...hat.com>
Cc:	Hari Bathini <hbathini@...ux.vnet.ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>, thuth@...hat.com,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc: on crash, kexec'ed kernel needs all CPUs are
 online

On Wed, 4 Nov 2015 14:54:51 +0100
Laurent Vivier <lvivier@...hat.com> wrote:

> 
> 
> On 04/11/2015 13:34, Hari Bathini wrote:
> > On 10/16/2015 12:30 AM, 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.".
> >>
> >> Starting with POWER8, subcore logic relies on all threads of
> >> core being booted. So, on startup kernel tries to start all
> >> threads, and asks OPAL (or RTAS) to start all CPUs (including
> >> threads). If a CPU has been offlined by the previous kernel,
> >> it has not been returned to OPAL, and thus OPAL cannot restart
> >> it: this CPU has been lost...
> >>
> >> Signed-off-by: Laurent Vivier<lvivier@...hat.com>
> > 
> > 
> > Hi Laurent,
> 
> Hi Hari,
> 
> > Sorry for jumping too late into this.
> 
> better late than never :)
> 
> > Are you seeing this issue even with the below patches:
> > 
> > pseries:
> > http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=c1caae3de46a072d0855729aed6e793e536a4a55

Unfortunately, this is unlikely to be relevant - this fixes a failure
while setting up the kexec.  The problem we see occurs once we've
booted the second kernel and it's attempting to bring up secondary CPUs.

> > opal/powernv:
> > https://github.com/open-power/skiboot/commit/9ee56b5
> 
> Very interesting. Is there a way to have a firmware with the fix ?

From Laurent's analysis of the crash, I don't think this will be
relevant either, but I'm not sure.  It would be very interesting to
know which (if any) released firmwares include this patch so we can
test it.

-- 
David Gibson <dgibson@...hat.com>
Senior Software Engineer, Virtualization, Red Hat

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