Re: [PATCH V2 02/02] MIPS: Init new mmu_context for each possibleCPU to avoid memory corruption

From: David Daney
Date: Wed Mar 20 2013 - 19:16:16 EST

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.

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@xxxxxxxxxx>

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

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

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;

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at