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

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Date:	Tue, 20 Jan 2009 08:54:40 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Li Zefan <lizf@...fujitsu.com>,
	Jaswinder Singh Rajput <jaswinder@...nel.org>,
	Nick Piggin <npiggin@...e.de>
Cc:	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!


* 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.

	Ingo
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