Re: [RFC PATCH for -mm 4/5] fix mlock return value at munmap race

[Lee Schermerhorn <Lee.Schermerhorn@hp.com>]

On Mon, 2008-08-11 at 16:07 +0900, KOSAKI Motohiro wrote:
> Now, We call downgrade_write(&mm->mmap_sem) at begin of mlock.
> It increase mlock scalability.
> 
> But if mlock and munmap conflict happend, We can find vma gone.
> At that time, kernel should return ENOMEM because mlock after munmap return ENOMEM.
> (in addition, EAGAIN indicate "please try again", but mlock() called again cause error again)
> 
> This problem is theoretical issue.
> I can't reproduce that vma gone on my box, but fixes is better.

OK.

Reviewed-by:  Lee Schermerhorn <lee.schermerhorn@hp.com>

> 
> 
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> 
> ---
>  mm/mlock.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> Index: b/mm/mlock.c
> ===================================================================
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -296,7 +296,7 @@ int mlock_vma_pages_range(struct vm_area
>  		vma = find_vma(mm, start);
>  		/* non-NULL vma must contain @start, but need to check @end */
>  		if (!vma ||  end > vma->vm_end)
> -			return -EAGAIN;
> +			return -ENOMEM;
>  		return error;
>  	}
>  
> @@ -410,7 +410,7 @@ success:
>  		*prev = find_vma(mm, start);
>  		/* non-NULL *prev must contain @start, but need to check @end */
>  		if (!(*prev) || end > (*prev)->vm_end)
> -			ret = -EAGAIN;
> +			ret = -ENOMEM;
>  	} else {
>  		/*
>  		 * TODO:  for unlocking, pages will already be resident, so
> 
> 

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