[PATCH v2] mm: vmscan: add VM_BUG_ON on illegal return values from scan_objects

[Oskar Andero]

Add a VM_BUG_ON to catch any illegal value from the shrinkers. It's a
potential bug if scan_objects returns a negative other than -1 and
would lead to undefined behaviour.

Cc: Glauber Costa <glommer@xxxxxxxxxx>
Cc: Dave Chinner <dchinner@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Oskar Andero <oskar.andero@xxxxxxxxxxxxxx>
---
 mm/vmscan.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 6bac41e..63fec86 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;
+		VM_BUG_ON(ret < -1);
 		freed += ret;
 
 		count_vm_events(SLABS_SCANNED, nr_to_scan);
-- 
1.8.1.5

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