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Date:	Mon, 22 Sep 2014 07:11:53 +0800
From:	Wanpeng Li <kernellwp@...il.com>
To:	Wanpeng Li <wanpeng.li@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>, hpa@...or.com,
	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...nel.org>, x86@...nel.org,
	Borislav Petkov <bp@...en8.de>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	Prarit Bhargava <prarit@...hat.com>,
	Steven Rostedt <srostedt@...hat.com>,
	Toshi Kani <toshi.kani@...com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5] x86, cpu-hotplug: fix llc shared map unreleased during
 cpu hotplug

Ping Ingo, Peter Z, HPA,

于 14-9-17 下午3:17, Wanpeng Li 写道:
> 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@...com>
> Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
> Tested-by: Linn Crosetto <linn@...com>
> Signed-off-by: Wanpeng Li <wanpeng.li@...ux.intel.com>
> ---
> v4 -> v5:
>  * add the description when the bug can occur
> v3 -> v4:
>  * simplify backtrace
> v2 -> v3:
>  * simplify backtrace 
> v1 -> v2:
>  * fix subject line
>
>  arch/x86/kernel/smpboot.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index 5492798..0134ec7 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -1292,6 +1292,9 @@ static void remove_siblinginfo(int cpu)
>  
>  	for_each_cpu(sibling, cpu_sibling_mask(cpu))
>  		cpumask_clear_cpu(cpu, cpu_sibling_mask(sibling));
> +	for_each_cpu(sibling, cpu_llc_shared_mask(cpu))
> +		cpumask_clear_cpu(cpu, cpu_llc_shared_mask(sibling));
> +	cpumask_clear(cpu_llc_shared_mask(cpu));
>  	cpumask_clear(cpu_sibling_mask(cpu));
>  	cpumask_clear(cpu_core_mask(cpu));
>  	c->phys_proc_id = 0;

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