linux-kernel - Re: [PATCH] mm: Fix mem_cgroup_oom

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Message-ID: <20170905164342.wrzof7kn4o4ybeg5@dhcp22.suse.cz>
Date:   Tue, 5 Sep 2017 18:43:42 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Laurent Dufour <ldufour@...ux.vnet.ibm.com>
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        kirill@...temov.name, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: Fix mem_cgroup_oom_disable() call missing

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@...ux.vnet.ibm.com>

Acked-by: Michal Hocko <mhocko@...e.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