blk-throttle: fix potential NULL pointer dereference in throtl_select_dispatch

tg in throtl_select_dispatch is used first and then do check. Since tg
may be NULL, it has potential NULL pointer dereference risk. So fix
it.

Signed-off-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Signed-off-by: Liu Bo <bo.liu@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index f63d88c..35bed77 100644 (file)
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -1207,7 +1207,7 @@ static int throtl_select_dispatch(struct throtl_service_queue *parent_sq)
 
        while (1) {
                struct throtl_grp *tg = throtl_rb_first(parent_sq);
-               struct throtl_service_queue *sq = &tg->service_queue;
+               struct throtl_service_queue *sq;
 
                if (!tg)
                        break;
@@ -1219,6 +1219,7 @@ static int throtl_select_dispatch(struct throtl_service_queue *parent_sq)
 
                nr_disp += throtl_dispatch_tg(tg);
 
+               sq = &tg->service_queue;
                if (sq->nr_queued[0] || sq->nr_queued[1])
                        tg_update_disptime(tg);