[PATCH] block: Fix elevator_get_default() to check for null q->tag_set

[SurajSonawane2415 <surajsonawane0215@gmail.com>]

Fix null pointer error by checking if q->tag_set is null.
Address "block/elevator.c:569 elevator_get_default() error:
we previously assumed 'q->tag_set' could be null (see line 565)"
This change prevents errors by making sure q->tag_set is valid
before accessing its flags.

Signed-off-by: SurajSonawane2415 <surajsonawane0215@gmail.com>
---
 block/elevator.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/block/elevator.c b/block/elevator.c
index 4122026b1..9ca32a6bd 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -562,12 +562,14 @@ static inline bool elv_support_iosched(struct request_queue *q)
  */
 static struct elevator_type *elevator_get_default(struct request_queue *q)
 {
-	if (q->tag_set && q->tag_set->flags & BLK_MQ_F_NO_SCHED_BY_DEFAULT)
-		return NULL;
+	if (q->tag_set) {
+		if (q->tag_set->flags & BLK_MQ_F_NO_SCHED_BY_DEFAULT)
+			return NULL;
 
-	if (q->nr_hw_queues != 1 &&
-	    !blk_mq_is_shared_tags(q->tag_set->flags))
-		return NULL;
+		if (q->nr_hw_queues != 1 &&
+			!blk_mq_is_shared_tags(q->tag_set->flags))
+			return NULL;
+	}
 
 	return elevator_find_get(q, "mq-deadline");
 }
-- 
2.34.1