[PATCH] mm: Fix mem_cgroup_oom_disable() call missing

[PATCH] mm: Fix mem_cgroup_oom_disable() call missing

[Laurent Dufour]

Seen while reading the code, in handle_mm_fault(), in the case
arch_vma_access_permitted() is failing the call to mem_cgroup_oom_disable()
is not made.

To fix that, move the call to mem_cgroup_oom_enable() after calling
arch_vma_access_permitted() as it should not have entered the memcg OOM.

Fixes: bae473a423f6 ("mm: introduce fault_env")
Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
---
 mm/memory.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 56e48e4593cb..274547075486 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3888,6 +3888,11 @@ int handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
 	/* do counter updates before entering really critical section. */
 	check_sync_rss_stat(current);
 
+	if (!arch_vma_access_permitted(vma, flags & FAULT_FLAG_WRITE,
+					    flags & FAULT_FLAG_INSTRUCTION,
+					    flags & FAULT_FLAG_REMOTE))
+		return VM_FAULT_SIGSEGV;
+
 	/*
 	 * Enable the memcg OOM handling for faults triggered in user
 	 * space.  Kernel faults are handled more gracefully.
@@ -3895,11 +3900,6 @@ int handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
 	if (flags & FAULT_FLAG_USER)
 		mem_cgroup_oom_enable();
 
-	if (!arch_vma_access_permitted(vma, flags & FAULT_FLAG_WRITE,
-					    flags & FAULT_FLAG_INSTRUCTION,
-					    flags & FAULT_FLAG_REMOTE))
-		return VM_FAULT_SIGSEGV;
-
 	if (unlikely(is_vm_hugetlb_page(vma)))
 		ret = hugetlb_fault(vma->vm_mm, vma, address, flags);
 	else
-- 
2.7.4

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Re: [PATCH] mm: Fix mem_cgroup_oom_disable() call missing

[Kirill A. Shutemov]

On Tue, Sep 05, 2017 at 05:30:39PM +0200, Laurent Dufour wrote:
> Seen while reading the code, in handle_mm_fault(), in the case
> arch_vma_access_permitted() is failing the call to mem_cgroup_oom_disable()
> is not made.
> 
> To fix that, move the call to mem_cgroup_oom_enable() after calling
> arch_vma_access_permitted() as it should not have entered the memcg OOM.
> 
> Fixes: bae473a423f6 ("mm: introduce fault_env")
> Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>

Ouch. Sorry for this.

Acked-by: Kirill A. Shutemov <kirill@shutemov.name>

Cc: stable@ is needed too.

It's strange we haven't seen reports of warning from
mem_cgroup_oom_enable().

-- 
 Kirill A. Shutemov

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Re: [PATCH] mm: Fix mem_cgroup_oom_disable() call missing

[Laurent Dufour]

On 05/09/2017 17:46, Kirill A. Shutemov wrote:
> On Tue, Sep 05, 2017 at 05:30:39PM +0200, Laurent Dufour wrote:
>> Seen while reading the code, in handle_mm_fault(), in the case
>> arch_vma_access_permitted() is failing the call to mem_cgroup_oom_disable()
>> is not made.
>>
>> To fix that, move the call to mem_cgroup_oom_enable() after calling
>> arch_vma_access_permitted() as it should not have entered the memcg OOM.
>>
>> Fixes: bae473a423f6 ("mm: introduce fault_env")
>> Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
> 
> Ouch. Sorry for this.
> 
> Acked-by: Kirill A. Shutemov <kirill@shutemov.name>
> 
> Cc: stable@ is needed too.

Andrew, should I resent it with stable in copy ?

> 
> It's strange we haven't seen reports of warning from
> mem_cgroup_oom_enable().

AFAIU, arch_vma_access_permitted() is only defined for x86 and it is
failing only in the case of the protection key mismatch, not so much used
for now...

Cheers,
Laurent.

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Re: [PATCH] mm: Fix mem_cgroup_oom_disable() call missing

[Michal Hocko]

On Tue 05-09-17 17:30:39, Laurent Dufour wrote:
> Seen while reading the code, in handle_mm_fault(), in the case
> arch_vma_access_permitted() is failing the call to mem_cgroup_oom_disable()
> is not made.
> 
> To fix that, move the call to mem_cgroup_oom_enable() after calling
> arch_vma_access_permitted() as it should not have entered the memcg OOM.
> 
> Fixes: bae473a423f6 ("mm: introduce fault_env")
> Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  mm/memory.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index 56e48e4593cb..274547075486 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3888,6 +3888,11 @@ int handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
>  	/* do counter updates before entering really critical section. */
>  	check_sync_rss_stat(current);
>  
> +	if (!arch_vma_access_permitted(vma, flags & FAULT_FLAG_WRITE,
> +					    flags & FAULT_FLAG_INSTRUCTION,
> +					    flags & FAULT_FLAG_REMOTE))
> +		return VM_FAULT_SIGSEGV;
> +
>  	/*
>  	 * Enable the memcg OOM handling for faults triggered in user
>  	 * space.  Kernel faults are handled more gracefully.
> @@ -3895,11 +3900,6 @@ int handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
>  	if (flags & FAULT_FLAG_USER)
>  		mem_cgroup_oom_enable();
>  
> -	if (!arch_vma_access_permitted(vma, flags & FAULT_FLAG_WRITE,
> -					    flags & FAULT_FLAG_INSTRUCTION,
> -					    flags & FAULT_FLAG_REMOTE))
> -		return VM_FAULT_SIGSEGV;
> -
>  	if (unlikely(is_vm_hugetlb_page(vma)))
>  		ret = hugetlb_fault(vma->vm_mm, vma, address, flags);
>  	else
> -- 
> 2.7.4
> 
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-- 
Michal Hocko
SUSE Labs

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