linux-kernel - Re: [PATCH] mm: /proc/pid/clear_refs: no need to clear VM_SOFTDIRTY in clear_soft_dirty

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Message-ID: <20151216174348.GA19144@node.shutemov.name>
Date:	Wed, 16 Dec 2015 19:43:49 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: /proc/pid/clear_refs: no need to clear VM_SOFTDIRTY
 in clear_soft_dirty_pmd()

On Wed, Dec 16, 2015 at 06:26:32PM +0100, Oleg Nesterov wrote:
> clear_soft_dirty_pmd() is called by clear_refs_write(CLEAR_REFS_SOFT_DIRTY),
> VM_SOFTDIRTY was already cleared before walk_page_range().

Not only that, We shouldn't [generally] change vm_flags without exclusive
mmap_sem and we have only down_read() here.

> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

> ---
>  fs/proc/task_mmu.c |    3 ---
>  1 files changed, 0 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 187b3b5..1a02b15 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -817,9 +817,6 @@ static inline void clear_soft_dirty_pmd(struct vm_area_struct *vma,
>  	pmd = pmd_wrprotect(pmd);
>  	pmd = pmd_clear_soft_dirty(pmd);
>  
> -	if (vma->vm_flags & VM_SOFTDIRTY)
> -		vma->vm_flags &= ~VM_SOFTDIRTY;
> -
>  	set_pmd_at(vma->vm_mm, addr, pmdp, pmd);
>  }
>  #else
> -- 
> 1.5.5.1
> 
> 
> --
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-- 
 Kirill A. Shutemov
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