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

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Message-Id: <1363524614-3823-1-git-send-email-chenhc@lemote.com>
Date:	Sun, 17 Mar 2013 20:50:14 +0800
From:	Huacai Chen <chenhc@...ote.com>
To:	Ralf Baechle <ralf@...ux-mips.org>
Cc:	linux-mips@...ux-mips.org, linux-kernel@...r.kernel.org,
	Fuxin Zhang <zhangfx@...ote.com>,
	Zhangjin Wu <wuzhangjin@...il.com>,
	Huacai Chen <chenhc@...ote.com>
Subject: [PATCH V2 02/02] MIPS: Init new mmu_context for each possible CPU to avoid memory corruption

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>
---
 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;
-- 
1.7.7.3

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