nvme-fc: use separate work queue to avoid warning

When tearing down a controller the following warning is issued:

WARNING: CPU: 0 PID: 30681 at ../kernel/workqueue.c:2418 check_flush_dependency

This happens as the err_work workqueue item is scheduled on the
system workqueue (which has WQ_MEM_RECLAIM not set), but is flushed
from a workqueue which has WQ_MEM_RECLAIM set.

Fix this by providing an FC-NVMe specific workqueue.

Fixes: 4cff280a ("nvme-fc: resolve io failures during connect")
Signed-off-by: NHannes Reinecke <hare@suse.com>
Reviewed-by: NJames Smart <james.smart@broadcom.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>

drivers/nvme/host/fc.c

@@ -202,7 +202,7 @@ static LIST_HEAD(nvme_fc_lport_list);
 static DEFINE_IDA(nvme_fc_local_port_cnt);
 static DEFINE_IDA(nvme_fc_ctrl_cnt);
 
-
+static struct workqueue_struct *nvme_fc_wq;
 
 /*
  * These items are short-term. They will eventually be moved into
@@ -2054,7 +2054,7 @@ nvme_fc_error_recovery(struct nvme_fc_ctrl *ctrl, char *errmsg)
 	 */
 	if (ctrl->ctrl.state == NVME_CTRL_CONNECTING) {
 		active = atomic_xchg(&ctrl->err_work_active, 1);
-		if (!active && !schedule_work(&ctrl->err_work)) {
+		if (!active && !queue_work(nvme_fc_wq, &ctrl->err_work)) {
 			atomic_set(&ctrl->err_work_active, 0);
 			WARN_ON(1);
 		}
@@ -3399,6 +3399,10 @@ static int __init nvme_fc_init_module(void)
 {
 	int ret;
 
+	nvme_fc_wq = alloc_workqueue("nvme_fc_wq", WQ_MEM_RECLAIM, 0);
+	if (!nvme_fc_wq)
+		return -ENOMEM;
+
 	/*
 	 * NOTE:
 	 * It is expected that in the future the kernel will combine
@@ -3416,7 +3420,7 @@ static int __init nvme_fc_init_module(void)
 	ret = class_register(&fc_class);
 	if (ret) {
 		pr_err("couldn't register class fc\n");
-		return ret;
+		goto out_destroy_wq;
 	}
 
 	/*
@@ -3440,6 +3444,9 @@ static int __init nvme_fc_init_module(void)
 	device_destroy(&fc_class, MKDEV(0, 0));
 out_destroy_class:
 	class_unregister(&fc_class);
+out_destroy_wq:
+	destroy_workqueue(nvme_fc_wq);
+
 	return ret;
 }
 
@@ -3456,6 +3463,7 @@ static void __exit nvme_fc_exit_module(void)
 
 	device_destroy(&fc_class, MKDEV(0, 0));
 	class_unregister(&fc_class);
+	destroy_workqueue(nvme_fc_wq);
 }
 
 module_init(nvme_fc_init_module);