blk-mq: don't create hctx debugfs dir until q->debugfs_dir is created

stable inclusion
from stable-v5.10.137
commit ed6ae2381150bd8235e5f8460913ea6152bde2e1
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I60PLB

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ed6ae2381150bd8235e5f8460913ea6152bde2e1

--------------------------------

[ Upstream commit f3ec5d11 ]

blk_mq_debugfs_register_hctx() can be called by blk_mq_update_nr_hw_queues
when gendisk isn't added yet, such as nvme tcp.

Fixes the warning of 'debugfs: Directory 'hctx0' with parent '/' already present!'
which can be observed reliably when running blktests nvme/005.

Fixes: 6cfc0081 ("blk-mq: no need to check return value of debugfs_create functions")
Reported-by: NYi Zhang <yi.zhang@redhat.com>
Signed-off-by: NMing Lei <ming.lei@redhat.com>
Tested-by: NYi Zhang <yi.zhang@redhat.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220711090808.259682-1-ming.lei@redhat.comSigned-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>

block/blk-mq-debugfs.c

@@ -915,6 +915,9 @@ void blk_mq_debugfs_register_hctx(struct request_queue *q,
 	char name[20];
 	int i;
 
+	if (!q->debugfs_dir)
+		return;
+
 	snprintf(name, sizeof(name), "hctx%u", hctx->queue_num);
 	hctx->debugfs_dir = debugfs_create_dir(name, q->debugfs_dir);