linux-kernel - Re: [PATCH V4 1/6] mm: mlock: Refactor mlock, munlock, and munlockall code

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Date:	Wed, 22 Jul 2015 13:42:26 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Eric B Munson <emunson@...mai.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>,
	Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V4 1/6] mm: mlock: Refactor mlock, munlock, and
 munlockall code

On Tue, Jul 21, 2015 at 03:59:36PM -0400, Eric B Munson wrote:
> @@ -648,20 +656,23 @@ SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
>  	start &= PAGE_MASK;
>  
>  	down_write(&current->mm->mmap_sem);
> -	ret = do_mlock(start, len, 0);
> +	ret = apply_vma_flags(start, len, flags, false);
>  	up_write(&current->mm->mmap_sem);
>  
>  	return ret;
>  }
>  
> +SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
> +{
> +	return do_munlock(start, len, VM_LOCKED);
> +}
> +
>  static int do_mlockall(int flags)
>  {
>  	struct vm_area_struct * vma, * prev = NULL;
>  
>  	if (flags & MCL_FUTURE)
>  		current->mm->def_flags |= VM_LOCKED;
> -	else
> -		current->mm->def_flags &= ~VM_LOCKED;

I think this is wrong.

With current code mlockall(MCL_CURRENT) after mlockall(MCL_FUTURE |
MCL_CURRENT) would undo future mlocking, without unlocking currently
mlocked memory.

The change will break the use-case.

>  	if (flags == MCL_FUTURE)
>  		goto out;
>  

-- 
 Kirill A. Shutemov
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