linux-kernel - Re: [BUG] kernel BUG at arch/x86/kernel/tlb

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Date:	Tue, 20 Jan 2009 16:20:07 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Jaswinder Singh Rajput <jaswinder@...nel.org>,
	Nick Piggin <npiggin@...e.de>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Mike Travis <travis@....com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] kernel BUG at arch/x86/kernel/tlb_32.c:130!

Ingo Molnar wrote:
> * Ingo Molnar <mingo@...e.hu> wrote:
> 
>> * Li Zefan <lizf@...fujitsu.com> wrote:
>>
>>> I was using mmotm 2009-01-16-16-18, and I ran into this BUG,
>>> the line is:
>>> 	BUG_ON(cpumask_empty(cpumask));
>>>
>>> I suspect it is caused by:
>>>
>>> commit 4595f9620cda8a1e973588e743cf5f8436dd20c6
>>> Author: Rusty Russell <rusty@...tcorp.com.au>
>>> Date:   Sat Jan 10 21:58:09 2009 -0800
>>>
>>>     x86: change flush_tlb_others to take a const struct cpumask
>>>
>>>     Impact: reduce stack usage, use new cpumask API.
>> Jaswinder reported a similar crash.
>>
>> Mike, Rusty, what's going on with this commit? Why does this code:
>>
>> +       if (cpumask_any_but(&mm->cpu_vm_mask, smp_processor_id()) < nr_cpu_ids)
>> +               flush_tlb_others(&mm->cpu_vm_mask, mm, TLB_FLUSH_ALL);
>>
>> Assume that mm->cpu_vm_mask wont change? TLB flushes go async and the 
>> MM's schedulability is not locked during that. I.e. mm->cpu_vm_mask can 
>> change under you while the TLB flush IPIs are flying around - while when 
>> the cpumask was passed on-stack this wouldnt happen.
> 
> okay, a testsystem of mine just triggered this crash too.
> 
> Li Zefan, Jaswinder, does the patch below fix it for you?
> 

I'll test it, but I have to run for several hours to confirm it, since
the bug is not easy to trigger. :)

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