linux-kernel - Re: [shm][hugetlb] Fix get_policy for stacked shared memory files

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Message-Id: <20070611213020.b3d91757.akpm@linux-foundation.org>
Date:	Mon, 11 Jun 2007 21:30:20 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Adam Litke <agl@...ibm.com>
Cc:	dean gaudet <dean@...tic.org>,
	William Lee Irwin III <wli@...omorphy.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-kernel@...r.kernel.org, ak@...e.de, clameter@....com
Subject: Re: [shm][hugetlb] Fix get_policy for stacked shared memory files

On Mon, 11 Jun 2007 16:34:54 -0500 Adam Litke <agl@...ibm.com> wrote:

> Here's another breakage as a result of shared memory stacked files :(
> 
> The NUMA policy for a VMA is determined by checking the following (in the order
> given):
> 
> 1) vma->vm_ops->get_policy() (if defined)
> 2) vma->vm_policy (if defined)
> 3) task->mempolicy (if defined)
> 4) Fall back to default_policy
> 
> By switching to stacked files for shared memory, get_policy() is now always set
> to shm_get_policy which is a wrapper function.  This causes us to stop at step
> 1, which yields NULL for hugetlb instead of task->mempolicy which was the
> previous (and correct) result.
> 
> This patch modifies the shm_get_policy() wrapper to maintain steps 1-3 for the
> wrapped vm_ops.  Andi and Christoph, does this look right to you?
> 

Can we just double-check the refcounting please?

> index 4fefbad..8d2672d 100644
> --- a/ipc/shm.c
> +++ b/ipc/shm.c
> @@ -254,8 +254,10 @@ struct mempolicy *shm_get_policy(struct vm_area_struct *vma, unsigned long addr)
>  
>  	if (sfd->vm_ops->get_policy)
>  		pol = sfd->vm_ops->get_policy(vma, addr);

afacit this takes a ref on the underlying policy

> -	else
> +	else if (vma->vm_policy)
>  		pol = vma->vm_policy;
> +	else
> +		pol = current->mempolicy;

but these two do not.

>  	return pol;
>  }
>  #endif

Is is all correct?
-
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