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SubjectRe: [PATCH] mm: vmscan: add BUG_ON on illegal return values from scan_objects
On Mon, 20 May 2013, Oskar Andero wrote:

> Add a BUG_ON to catch any illegal value from the shrinkers. This fixes a
> potential bug if scan_objects returns a negative other than -1, which
> would lead to undefined behaviour.
>
> Cc: Glauber Costa <glommer@openvz.org>
> Cc: Dave Chinner <dchinner@redhat.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Oskar Andero <oskar.andero@sonymobile.com>
> ---
> mm/vmscan.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 6bac41e..fbe6742 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -293,6 +293,7 @@ shrink_slab_one(struct shrinker *shrinker, struct shrink_control *shrinkctl,
> ret = shrinker->scan_objects(shrinker, shrinkctl);
> if (ret == -1)
> break;
> + BUG_ON(ret < -1);
> freed += ret;
>
> count_vm_events(SLABS_SCANNED, nr_to_scan);

Nack, this doesn't fix anything. I can see the intention, and for that it
might make sense to turn this into VM_BUG_ON() so that anybody debugging
an issue related to this with CONFIG_DEBUG_VM would get the indication,
but I don't think we need to enforce the API with BUG_ON().


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