nvme: don't call blk_mq_{,un}quiesce_tagset when ctrl->tagset is NULL

The NVMe drivers support a mode where no tagset is allocated for the I/O
queues and only the admin queue is usable.  In that case ctrl->tagset is
NULL and we must not call the block per-tagset quiesce helpers that
dereference it.

Fixes: 98d81f0 ("nvme: use blk_mq_[un]quiesce_tagset")
Reported-by: Gerd Bayer <[email protected]>
Reported-by: Chao Leng <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Chao Leng <[email protected]>

Author: Christoph Hellwig

drivers/nvme/host/core.c

@@ -5215,6 +5215,8 @@ EXPORT_SYMBOL_GPL(nvme_start_freeze);
 
 void nvme_quiesce_io_queues(struct nvme_ctrl *ctrl)
 {
+	if (!ctrl->tagset)
+		return;
 	if (!test_and_set_bit(NVME_CTRL_STOPPED, &ctrl->flags))
 		blk_mq_quiesce_tagset(ctrl->tagset);
 	else
@@ -5224,6 +5226,8 @@ EXPORT_SYMBOL_GPL(nvme_quiesce_io_queues);
 
 void nvme_unquiesce_io_queues(struct nvme_ctrl *ctrl)
 {
+	if (!ctrl->tagset)
+		return;
 	if (test_and_clear_bit(NVME_CTRL_STOPPED, &ctrl->flags))
 		blk_mq_unquiesce_tagset(ctrl->tagset);
 }