Date: Thu, 31 May 2012 13:45:13 -0700 (PDT)
From: David Rientjes <rientjes@google.com>
To: Andi Kleen <andi@firstfloor.org>
cc: linux-kernel@vger.kernel.org, Andi Kleen <ak@linux.intel.com>,
        penberg@kernel.org, cl@linux.com
Subject: Re: [PATCH] slab/mempolicy: always use local policy from interrupt
 context v3
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References: <1338438844-5022-1-git-send-email-andi@firstfloor.org>
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On Wed, 30 May 2012, Andi Kleen wrote:

> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index cfb6c86..b65eb06 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1586,9 +1586,11 @@ static unsigned interleave_nodes(struct mempolicy *policy)
>   * task can change it's policy.  The system default policy requires no
>   * such protection.
>   */
> -unsigned slab_node(struct mempolicy *policy)
> +unsigned slab_node(void)
>  {
> -	if (!policy || policy->flags & MPOL_F_LOCAL)
> +	struct mempolicy *policy = current->mempolicy;
> +
> +	if (in_interrupt() || !policy || policy->flags & MPOL_F_LOCAL)
>  		return numa_node_id();
>  
>  	switch (policy->mode) {

I think the version proposed by David Mackey is more clear, it makes it 
obvious that we don't want to dereference current in interrupt context 
whereas that relies on short-circuiting your conditional in your approach.
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