* [PATCH V2 02/02] MIPS: Init new mmu_context for each possible CPU to avoid memory corruption
@ 2013-03-17 12:50 Huacai Chen
2013-03-20 5:49 ` Chen Jie
2013-03-20 23:16 ` David Daney
0 siblings, 2 replies; 3+ messages in thread
From: Huacai Chen @ 2013-03-17 12:50 UTC (permalink / raw)
To: Ralf Baechle
Cc: linux-mips, linux-kernel, Fuxin Zhang, Zhangjin Wu, Huacai Chen
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@lemote.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
^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [PATCH V2 02/02] MIPS: Init new mmu_context for each possible CPU to avoid memory corruption
2013-03-17 12:50 [PATCH V2 02/02] MIPS: Init new mmu_context for each possible CPU to avoid memory corruption Huacai Chen
@ 2013-03-20 5:49 ` Chen Jie
2013-03-20 23:16 ` David Daney
1 sibling, 0 replies; 3+ messages in thread
From: Chen Jie @ 2013-03-20 5:49 UTC (permalink / raw)
To: Huacai Chen
Cc: Ralf Baechle, linux-mips, linux-kernel, Fuxin Zhang, Zhangjin Wu
2013/3/17 Huacai Chen <chenhc@lemote.com>:
> 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.
Adds some further explanations about point 5:
5.1) The parent process runs on CPU#1, the version field of its
asid[CPU#1] and CPU#1's asid cache may match, thus the parent
process's asid[CPU#1] is used in TLB refilling routine.
5.2) Then the child process runs on CPU#1 which probably has the same
asid[CPU#1] as its parent(as pointed by point 3).
5.3) The child process may access address space of its parent.
It can also be solved by increasing version field of asid cache when
plugin a CPU, may be a better way?
Regards,
-- Chen Jie
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH V2 02/02] MIPS: Init new mmu_context for each possible CPU to avoid memory corruption
2013-03-17 12:50 [PATCH V2 02/02] MIPS: Init new mmu_context for each possible CPU to avoid memory corruption Huacai Chen
2013-03-20 5:49 ` Chen Jie
@ 2013-03-20 23:16 ` David Daney
1 sibling, 0 replies; 3+ messages in thread
From: David Daney @ 2013-03-20 23:16 UTC (permalink / raw)
To: Huacai Chen
Cc: Ralf Baechle, linux-mips, linux-kernel, Fuxin Zhang, Zhangjin Wu
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@lemote.com>
We were seeing the same crashes, this patch set seems to fix the problem.
Acked-by: David Daney <david.daney@cavium.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;
>
^ permalink raw reply [flat|nested] 3+ messages in thread
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2013-03-17 12:50 [PATCH V2 02/02] MIPS: Init new mmu_context for each possible CPU to avoid memory corruption Huacai Chen
2013-03-20 5:49 ` Chen Jie
2013-03-20 23:16 ` David Daney
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