mm: fix null pointer dereference in wait_iff_congested()

An unintended consequence of commit 4ae0a48 ("mm: modify pgdat_balanced() so that it also handles order-0") 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 <[email protected]> Reported-and-tested-by: Sedat Dilek <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Mel Gorman <[email protected]> Cc: Hugh Dickins <[email protected]> Signed-off-by: Zlatko Calusic <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
tiwai · Dec 28, 2012 · ecccd12 · ecccd12
1 parent 101e5c7
commit ecccd12
Showing 1 changed file with 1 addition and 1 deletion.
diff --git a/mm/vmscan.c b/mm/vmscan.c
@@ -2775,7 +2775,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
 		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);
 		}