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From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Guillaume Autran <gautran@mrv.com>
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Date: Wed, 13 Jul 2005 10:09:52 +1000
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Cc: akpm@osdl.org, linuxppc-embedded@ozlabs.org
Subject: Re: [PATCH] ppc32: fix destroy_context() race condition
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On Tue, 2005-07-12 at 10:23 -0400, Guillaume Autran wrote:
> Fix for a race condition when a task gets preempted by another task
> while executing the destroy_context(...) in a FEW_CONTEXTS environment.
> mm->context == NO_CONTEXT but the context_map may indicate all contexts
> are in use.
> The solution to this problem is to disable kernel preemption while
> destroying a MMU context.
> 
> Signed-off-by: Guillaume Autran <gautran@mrv.com>

Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

> 
> ---
> 
> diff -Nru a/include/asm-ppc/mmu_context.h b/include/asm-ppc/mmu_context.h
> --- a/include/asm-ppc/mmu_context.h	2005-06-17 15:48:29.000000000 -0400
> +++ b/include/asm-ppc/mmu_context.h	2005-07-05 08:58:46.000000000 -0400
> @@ -149,6 +149,7 @@
>  */
> static inline void destroy_context(struct mm_struct *mm)
> {
> +	preempt_disable();
> 	if (mm->context != NO_CONTEXT) {
> 		clear_bit(mm->context, context_map);
> 		mm->context = NO_CONTEXT;
> @@ -156,6 +157,7 @@
> 		atomic_inc(&nr_free_contexts);
> #endif
> 	}
> +	preempt_enable();
> }
> 
> static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
> 
> 
> 
> 
>