[PATCH V2] null_blk: cleanup null_init_tag_set

[Ming Lei <ming.lei@redhat.com>]

The passed 'nullb' can be NULL, so cause null ptr reference.

Fix the issue, meantime cleanup null_init_tag_set for avoiding to add
similar issue in future.

Meantime set BLK_MQ_F_NO_SCHED if g_no_sched is true in case of NULL
device, same with BLK_MQ_F_TAG_HCTX_SHARED.

Cc: Vincent Fu <vincent.fu@samsung.com>
Fixes: 37ae152c7a0d ("null_blk: add configfs variables for 2 options")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
V2:
	- set BLK_MQ_F_NO_SCHED & BLK_MQ_F_TAG_HCTX_SHARED correctly in case
	of null device, as suggested by Vincent Fu

 drivers/block/null_blk/main.c | 53 +++++++++++++++++++++++------------
 1 file changed, 35 insertions(+), 18 deletions(-)

diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
index c955a07dba2d..1501c85fc9e4 100644
--- a/drivers/block/null_blk/main.c
+++ b/drivers/block/null_blk/main.c
@@ -1898,31 +1898,48 @@ static int null_gendisk_register(struct nullb *nullb)
 
 static int null_init_tag_set(struct nullb *nullb, struct blk_mq_tag_set *set)
 {
+	unsigned int flags = BLK_MQ_F_SHOULD_MERGE;
+	int hw_queues, numa_node;
+	unsigned int queue_depth;
 	int poll_queues;
 
+	if (nullb) {
+		hw_queues = nullb->dev->submit_queues;
+		poll_queues = nullb->dev->poll_queues;
+		queue_depth = nullb->dev->hw_queue_depth;
+		numa_node = nullb->dev->home_node;
+		if (nullb->dev->no_sched)
+			flags |= BLK_MQ_F_NO_SCHED;
+		if (nullb->dev->shared_tag_bitmap)
+			flags |= BLK_MQ_F_TAG_HCTX_SHARED;
+		if (nullb->dev->blocking)
+			flags |= BLK_MQ_F_BLOCKING;
+	} else {
+		hw_queues = g_submit_queues;
+		poll_queues = g_poll_queues;
+		queue_depth = g_hw_queue_depth;
+		numa_node = g_home_node;
+		if (g_no_sched)
+			flags |= BLK_MQ_F_NO_SCHED;
+		if (g_shared_tag_bitmap)
+			flags |= BLK_MQ_F_TAG_HCTX_SHARED;
+		if (g_blocking)
+			flags |= BLK_MQ_F_BLOCKING;
+	}
+
 	set->ops = &null_mq_ops;
-	set->nr_hw_queues = nullb ? nullb->dev->submit_queues :
-						g_submit_queues;
-	poll_queues = nullb ? nullb->dev->poll_queues : g_poll_queues;
-	if (poll_queues)
-		set->nr_hw_queues += poll_queues;
-	set->queue_depth = nullb ? nullb->dev->hw_queue_depth :
-						g_hw_queue_depth;
-	set->numa_node = nullb ? nullb->dev->home_node : g_home_node;
 	set->cmd_size	= sizeof(struct nullb_cmd);
-	set->flags = BLK_MQ_F_SHOULD_MERGE;
-	if (nullb->dev->no_sched)
-		set->flags |= BLK_MQ_F_NO_SCHED;
-	if (nullb->dev->shared_tag_bitmap)
-		set->flags |= BLK_MQ_F_TAG_HCTX_SHARED;
+	set->flags = flags;
 	set->driver_data = nullb;
-	if (poll_queues)
+	set->nr_hw_queues = hw_queues;
+	set->queue_depth = queue_depth;
+	set->numa_node = numa_node;
+	if (poll_queues) {
+		set->nr_hw_queues += poll_queues;
 		set->nr_maps = 3;
-	else
+	} else {
 		set->nr_maps = 1;
-
-	if ((nullb && nullb->dev->blocking) || g_blocking)
-		set->flags |= BLK_MQ_F_BLOCKING;
+	}
 
 	return blk_mq_alloc_tag_set(set);
 }
-- 
2.31.1