linux-kernel - Re: [PATCH V2 02/02] MIPS: Init new mmu_context for each possible CPU to avoid memory corruption

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Message-ID: <514A4337.6080100@gmail.com>
Date:	Wed, 20 Mar 2013 16:16:07 -0700
From:	David Daney <ddaney.cavm@...il.com>
To:	Huacai Chen <chenhc@...ote.com>
CC:	Ralf Baechle <ralf@...ux-mips.org>, linux-mips@...ux-mips.org,
	linux-kernel@...r.kernel.org, Fuxin Zhang <zhangfx@...ote.com>,
	Zhangjin Wu <wuzhangjin@...il.com>
Subject: Re: [PATCH V2 02/02] MIPS: Init new mmu_context for each possible
 CPU to avoid memory corruption

On 03/17/2013 05:50 AM, Huacai Chen wrote:
> Currently, init_new_context() only for each online CPU, this may cause
> memory corruption when CPU hotplug and fork() happens at the same time.
> To avoid this, we make init_new_context() cover each possible CPU.
>
> Scenario:
> 1, CPU#1 is being offline;
> 2, On CPU#0, do_fork() call dup_mm() and copy a mm_struct to the child;
> 3, On CPU#0, dup_mm() call init_new_context(), since CPU#1 is offline
>     and init_new_context() only covers the online CPUs, child has the
>     same asid as its parent on CPU#1 (however, child's asid should be 0);
> 4, CPU#1 is being online;
> 5, Now, if both parent and child run on CPU#1, memory corruption (e.g.
>     segfault, bus error, etc.) will occur.
>
> Signed-off-by: Huacai Chen <chenhc@...ote.com>


We were seeing the same crashes, this patch set seems to fix the problem.

Acked-by: David Daney <david.daney@...ium.com>

> ---
>   arch/mips/include/asm/mmu_context.h |    2 +-
>   1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/arch/mips/include/asm/mmu_context.h b/arch/mips/include/asm/mmu_context.h
> index e81d719..49d220c 100644
> --- a/arch/mips/include/asm/mmu_context.h
> +++ b/arch/mips/include/asm/mmu_context.h
> @@ -133,7 +133,7 @@ init_new_context(struct task_struct *tsk, struct mm_struct *mm)
>   {
>   	int i;
>
> -	for_each_online_cpu(i)
> +	for_each_possible_cpu(i)
>   		cpu_context(i, mm) = 0;
>
>   	return 0;
>

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