From ecccd1248d6e6986130ffcc3b0d003cb46a485c0 Mon Sep 17 00:00:00 2001
From: Zlatko Calusic <zlatko.calusic@iskon.hr>
Date: Fri, 28 Dec 2012 03:16:38 +0100
Subject: [PATCH] mm: fix null pointer dereference in wait_iff_congested()
An unintended consequence of commit 4ae0a48b5efc ("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 <zliu@redhat.com>
Reported-and-tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Zlatko Calusic <zlatko.calusic@iskon.hr>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
mm/vmscan.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 23291b9ae8713..16b42af393ac0 100644
--- 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);
}
--
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