Re: [PATCH] mm: fix null pointer dereference in wait_iff_congested()

[Sedat Dilek]

Just FYI:

This patch landed upstream [1].
Thanks for all involved people.

- Sedat -

[1] http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=commitdiff;h=ecccd1248d6e6986130ffcc3b0d003cb46a485c0

On Fri, Dec 28, 2012 at 3:16 AM, Zlatko Calusic <zlatko.calusic@xxxxxxxx> wrote:
> From: Zlatko Calusic <zlatko.calusic@xxxxxxxx>
>
> The unintended consequence of commit 4ae0a48b is that
> wait_iff_congested() can now be called with NULL struct zone*
> producing kernel oops like this:
>
> BUG: unable to handle kernel NULL pointer dereference
> IP: [<ffffffff811542d9>] wait_iff_congested+0x59/0x140
>
> This trivial patch fixes it.
>
> Reported-by: Zhouping Liu <zliu@xxxxxxxxxx>
> Reported-and-tested-by: Sedat Dilek <sedat.dilek@xxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Signed-off-by: Zlatko Calusic <zlatko.calusic@xxxxxxxx>
> ---
>  mm/vmscan.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 02bcfa3..e55ce55 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2782,7 +2782,7 @@ loop_again:
>                 if (total_scanned && (sc.priority < DEF_PRIORITY - 2)) {
>                         if (has_under_min_watermark_zone)
>                                 count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
> -                       else
> +                       else if (unbalanced_zone)
>                                 wait_iff_congested(unbalanced_zone, BLK_RW_ASYNC, HZ/10);
>                 }
>
> --
> 1.8.1.rc3
>
> --
> Zlatko
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