[v02] REPOST powerpc/migration: Handle unitialized timer reset

[Michael Bringmann]

Hello, Michael:
    Please look at v03 of the patch set which was posted
just on 09/25/2018.  We had a last minute brainstorm of how
to simplify the code after the v02 REPOST.
    Also, note that we would like to invalidate the set,

[PATCH v08 0/5] powerpc/hotplug: Update affinity for migrated CPUs
https://lists.ozlabs.org/pipermail/linuxppc-dev/2018-July/176301.html

as we think it is covered now by other code.

    Thanks for your attention and assistance.

Michael

On 09/26/2018 07:13 AM, Michael Ellerman wrote:
> On Thu, 2018-09-20 at 16:45:13 UTC, Michael Bringmann wrote:
>> After migration of a powerpc LPAR, the kernel executes code to
>> update the system state to reflect new platform characteristics.
>> Such changes include modifications to device tree properties
>> provided to the system by PHYP.  Property notifications received
>> by the powerpc 'migration_store' code are passed along to the
>> kernel in general through a call to 'of_update_property' which
>> in turn passes such events back to all modules through entries like
>> the '.notifier_call' function within the NUMA module.  When the
>> NUMA module updates its state, it resets its event timer.  If this
>> occurs after a previous call to 'stop_topology_update' or on a
>> system without VPHN enabled, the code runs into an unitialized
>> timer structure and crashes.  This patch adds a safety check
>> along this path toward the problem code.
>>
>> Note: This crash was observed on every LPM in the 4.17-rc7 kernel
>> (and in the 4.18 kernel) of a system with dedicated CPUs enabled.
>> An example crash log without the patch is as follows.
>>
> ...
>>
>> Signed-off-by: Michael Bringmann <mwb at linux.vnet.ibm.com>
> 
> Applied to powerpc fixes, thanks.
> 
> https://git.kernel.org/powerpc/c/8604895a34d92f5e186ceb931b0d1b
> 
> cheers
> 
> 

-- 
Michael W. Bringmann
Linux Technology Center
IBM Corporation
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mwb at linux.vnet.ibm.com