Re: [PATCH v5] x86, cpu-hotplug: fix llc shared map unreleased during cpu hotplug

[Borislav Petkov]

On Wed, Sep 17, 2014 at 03:17:52PM +0800, Wanpeng Li wrote:
> BUG: unable to handle kernel NULL pointer dereference at 0000000000000004
> IP: [..] find_busiest_group
> PGD 5a9d5067 PUD 13067 PMD 0
> Oops: 0000 [#3] SMP
> [...]
> Call Trace:
> load_balance
> ? _raw_spin_unlock_irqrestore
> idle_balance
> __schedule
> schedule
> schedule_timeout
> ? lock_timer_base
> schedule_timeout_uninterruptible
> msleep
> lock_device_hotplug_sysfs
> online_store
> dev_attr_store
> sysfs_write_file
> vfs_write
> SyS_write
> system_call_fastpath
> 
> This bug can be triggered by hot add and remove large number of xen
> domain0's vcpus repeatedly.
> 
> Last level cache shared map is built during cpu up and build sched domain 
> routine takes advantage of it to setup sched domain cpu topology, however, 
> llc shared map is unreleased during cpu disable which lead to invalid sched 
> domain cpu topology. This patch fix it by release llc shared map correctly
> during cpu disable.
> 
> Reviewed-by: Toshi Kani <toshi.kani@xxxxxx>
> Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>
> Tested-by: Linn Crosetto <linn@xxxxxx>
> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxxxxxx>

Reviewed-by: Borislav Petkov <bp@xxxxxxx>

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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