[PATCH block/for-linus] blk-rq-qos: fix first node deletion of rq_qos_del()

[Tejun Heo]

rq_qos_del() incorrectly assigns the node being deleted to the head if
it was the first on the list in the !prev path.  Fix it by iterating
with ** instead.

Signed-off-by: Tejun Heo <t...@kernel.org>
Cc: Josef Bacik <jo...@toxicpanda.com>
Fixes: a79050434b45 ("blk-rq-qos: refactor out common elements of blk-wbt")
Cc: sta...@vger.kernel.org # v4.19+
---
 block/blk-rq-qos.h |   13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

--- a/block/blk-rq-qos.h
+++ b/block/blk-rq-qos.h
@@ -108,16 +108,13 @@ static inline void rq_qos_add(struct req
 
 static inline void rq_qos_del(struct request_queue *q, struct rq_qos *rqos)
 {
-       struct rq_qos *cur, *prev = NULL;
-       for (cur = q->rq_qos; cur; cur = cur->next) {
-               if (cur == rqos) {
-                       if (prev)
-                               prev->next = rqos->next;
-                       else
-                               q->rq_qos = cur;
+       struct rq_qos **cur;
+
+       for (cur = &q->rq_qos; *cur; cur = &(*cur)->next) {
+               if (*cur == rqos) {
+                       *cur = rqos->next;
                        break;
                }
-               prev = cur;
        }
 
        blk_mq_debugfs_unregister_rqos(rqos);