Re: [PATCH v4] x86, hotplug: fix llc shared map unreleased during cpu hotplug

From: Wanpeng Li
Date: Sun Sep 14 2014 - 21:32:40 EST


Ping Ingo, HPA, PeterZ
ä 14-9-4 äå5:34, Wanpeng Li åé:
Hi Ingo,
On Thu, Sep 04, 2014 at 04:56:41PM +0800, Wanpeng Li wrote:
On Thu, Sep 04, 2014 at 07:20:34AM +0200, Ingo Molnar wrote:
* Wanpeng Li <wanpeng.li@xxxxxxxxxxxxxxx> 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

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.
Very little is said in this changelog about how the bug was
found, how likely it is to occur for others, what systems are
affected, etc.
This bug can be triggered by hot add and remove large number of xen
domain0's vcpus repeated.

If I need to send a new version of the patch or you can pick the patch
w/ the updated changelog for me? ;-)

Regards,
Wanpeng Li

Regards,
Wanpeng Li

Thanks,

Ingo
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