Re: [BUG] kernel BUG at arch/x86/kernel/tlb_32.c:130!

From: Ingo Molnar
Date: Tue Jan 20 2009 - 02:55:23 EST

* Li Zefan <lizf@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx>
> 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.

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