nvme-auth: use workqueue dedicated to authentication

NVMe In-Band authentication uses two kinds of works: chap->auth_work and
ctrl->dhchap_auth_work. The latter work flushes or cancels the former
work. However, the both works are queued to the same workqueue nvme-wq.
It results in the lockdep WARNING as follows:

 WARNING: possible recursive locking detected
 6.2.0-rc4+ #1 Not tainted
 --------------------------------------------
 kworker/u16:7/69 is trying to acquire lock:
 ffff902d52e65548 ((wq_completion)nvme-wq){+.+.}-{0:0}, at: start_flush_work+0x2c5/0x380

 but task is already holding lock:
 ffff902d52e65548 ((wq_completion)nvme-wq){+.+.}-{0:0}, at: process_one_work+0x210/0x410

To avoid the WARNING, introduce a new workqueue nvme-auth-wq dedicated
to chap->auth_work.
Reported-by: Daniel Wagner <dwagner@suse.de>
Link: https://lore.kernel.org/linux-nvme/20230130110802.paafkiipmitwtnwr@carbon.lan/
Fixes: f50fff73 ("nvme: implement In-Band authentication")
Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Tested-by: Daniel Wagner <dwagner@suse.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/auth.c

@@ -45,6 +45,8 @@ struct nvme_dhchap_queue_context {
 	int sess_key_len;
 };
 
+struct workqueue_struct *nvme_auth_wq;
+
 #define nvme_auth_flags_from_qid(qid) \
 	(qid == 0) ? 0 : BLK_MQ_REQ_NOWAIT | BLK_MQ_REQ_RESERVED
 #define nvme_auth_queue_from_qid(ctrl, qid) \
@@ -866,7 +868,7 @@ int nvme_auth_negotiate(struct nvme_ctrl *ctrl, int qid)
 
 	chap = &ctrl->dhchap_ctxs[qid];
 	cancel_work_sync(&chap->auth_work);
-	queue_work(nvme_wq, &chap->auth_work);
+	queue_work(nvme_auth_wq, &chap->auth_work);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(nvme_auth_negotiate);
@@ -1008,10 +1010,15 @@ EXPORT_SYMBOL_GPL(nvme_auth_free);
 
 int __init nvme_init_auth(void)
 {
+	nvme_auth_wq = alloc_workqueue("nvme-auth-wq",
+			       WQ_UNBOUND | WQ_MEM_RECLAIM | WQ_SYSFS, 0);
+	if (!nvme_auth_wq)
+		return -ENOMEM;
+
 	nvme_chap_buf_cache = kmem_cache_create("nvme-chap-buf-cache",
 				CHAP_BUF_SIZE, 0, SLAB_HWCACHE_ALIGN, NULL);
 	if (!nvme_chap_buf_cache)
-		return -ENOMEM;
+		goto err_destroy_workqueue;
 
 	nvme_chap_buf_pool = mempool_create(16, mempool_alloc_slab,
 			mempool_free_slab, nvme_chap_buf_cache);
@@ -1021,6 +1028,8 @@ int __init nvme_init_auth(void)
 	return 0;
 err_destroy_chap_buf_cache:
 	kmem_cache_destroy(nvme_chap_buf_cache);
+err_destroy_workqueue:
+	destroy_workqueue(nvme_auth_wq);
 	return -ENOMEM;
 }
 
@@ -1028,4 +1037,5 @@ void __exit nvme_exit_auth(void)
 {
 	mempool_destroy(nvme_chap_buf_pool);
 	kmem_cache_destroy(nvme_chap_buf_cache);
+	destroy_workqueue(nvme_auth_wq);
 }