Re: PATCH: hugetlb: handle NODEMASK_ALLOC failure correctly

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 6 Jan 2011 11:04:39 +0100
Michal Hocko <mhocko@suse.cz> wrote:

> NODEMASK_ALLOC can use kmalloc if nodemask_t > 256 bytes so it might
> fail with NULL as a result. Let's check the resulting variable and
> fail with -ENOMEM if NODEMASK_ALLOC failed.
> 
> Signed-off-by: Michal Hocko <mhocko@suse.cz>
> ---
>  mm/hugetlb.c |   18 +++++++++++++++---
>  1 files changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 4c0606c..21f31b2 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1439,14 +1439,19 @@ static ssize_t nr_hugepages_store_common(bool obey_mempolicy,
>  	struct hstate *h;
>  	NODEMASK_ALLOC(nodemask_t, nodes_allowed, GFP_KERNEL | __GFP_NORETRY);
>  
> +	if (!nodes_allowed) {
> +		err = -ENOMEM;
> +		goto out;
> +	}

Looks good to me.  I was going to complain that it adds extra unneeded
instructions in the case where the nodemasks are allocated on the
stack.  But it appears that gcc assumes that stack-based variables
cannot have address zero, so if gcc sees this:

	{
		nodemask_t foo;

		if (!&foo) {
			stuff
		}
	}

if just removes it all for us.

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