[PATCH] block, bfq: initialize active lists for all actuators

[lirongqing <lirongqing@baidu.com>]

From: Li RongQing <lirongqing@baidu.com>

Commit 2d31c684a053 ("block, bfq: inject I/O to underutilized
actuators") extended bfqd->active_list from a single list_head to an
array indexed by actuator, but bfq_init_queue() still only initialized
the first two entries:

        INIT_LIST_HEAD(&bfqd->active_list[0]);
        INIT_LIST_HEAD(&bfqd->active_list[1]);

For devices with more than two independent access ranges, the remaining
list heads stay zeroed by kzalloc() and are never set up as empty lists.
When BFQ later adds a bfq_queue to one of those lists, list_add() writes
through head->next, which is NULL, corrupting the list or crashing the
kernel.

Initialize every actuator's active list using bfqd->num_actuators,
which is already set up earlier in bfq_init_queue().

Fixes: 2d31c684a053 ("block, bfq: inject I/O to underutilized actuators")
Signed-off-by: Li RongQing <lirongqing@baidu.com>
---
 block/bfq-iosched.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 0f75301..b21ddba 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -7273,8 +7273,8 @@ static int bfq_init_queue(struct request_queue *q, struct elevator_queue *eq)
 	bfqd->num_groups_with_pending_reqs = 0;
 #endif
 
-	INIT_LIST_HEAD(&bfqd->active_list[0]);
-	INIT_LIST_HEAD(&bfqd->active_list[1]);
+	for (i = 0; i < bfqd->num_actuators; i++)
+		INIT_LIST_HEAD(&bfqd->active_list[i]);
 	INIT_LIST_HEAD(&bfqd->idle_list);
 	INIT_HLIST_HEAD(&bfqd->burst_list);
 
-- 
2.9.4