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From: Lee Schermerhorn on 17 Mar 2010 10:20
On Tue, 2010-03-16 at 14:49 +0900, KOSAKI Motohiro wrote:
> ChangeLog from Ravikiran's original one
> - Fix the patch description. the problem is in mount, not only remount.
> - Skip mpol_new() simply, instead adding NULL check.
>
>
> =========================
> From: Ravikiran G Thirumalai <kiran(a)scalex86.org>
>
> Fix an 'oops' when a tmpfs mount point is mounted with the mpol=default
> mempolicy.
>
> Upon remounting a tmpfs mount point with 'mpol=default' option, the
> mount code crashed with a null pointer dereference. The initial
> problem report was on 2.6.27, but the problem exists in mainline
> 2.6.34-rc as well. On examining the code, we see that mpol_new returns
> NULL if default mempolicy was requested. This 'NULL' mempolicy is
> accessed to store the node mask resulting in oops.
>
> The following patch fixes it.
>
> Signed-off-by: Ravikiran Thirumalai <kiran(a)scalex86.org>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro(a)jp.fujitsu.com>
> Cc: Christoph Lameter <cl(a)linux-foundation.org>
> Cc: Mel Gorman <mel(a)csn.ul.ie>
> Cc: Lee Schermerhorn <lee.schermerhorn(a)hp.com>
> Cc: Hugh Dickins <hugh.dickins(a)tiscali.co.uk>
> Cc: <stable(a)kernel.org>

Acked-by: Lee Schermerhorn <lee.schermerhorn(a)hp.com>

> ---
> mm/mempolicy.c | 9 +++++++--
> 1 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index bda230e..25a0c0f 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -2213,10 +2213,15 @@ int mpol_parse_str(char *str, struct mempolicy **mpol, int no_context)
> goto out;
> mode = MPOL_PREFERRED;
> break;
> -
> + case MPOL_DEFAULT:
> + /*
> + * Insist on a empty nodelist
> + */
> + if (!nodelist)
> + err = 0;
> + goto out;
> /*
> * case MPOL_BIND: mpol_new() enforces non-empty nodemask.
> - * case MPOL_DEFAULT: mpol_new() enforces empty nodemask, ignores flags.
> */
> }
>

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