nvme: host delete_work and reset_work on separate workqueues

We need to ensure that delete_work will be hosted on a different
workqueue than all the works we flush or cancel from it.
Otherwise we may hit a circular dependency warning [1].

Also, given that delete_work flushes reset_work, host reset_work
on nvme_reset_wq and delete_work on nvme_delete_wq. In addition,
fix the flushing in the individual drivers to flush nvme_delete_wq
when draining queued deletes.

[1]:
[  178.491942] =============================================
[  178.492718] [ INFO: possible recursive locking detected ]
[  178.493495] 4.9.0-rc4-c844263313a8-lb #3 Tainted: G           OE
[  178.494382] ---------------------------------------------
[  178.495160] kworker/5:1/135 is trying to acquire lock:
[  178.495894]  (
[  178.496120] "nvme-wq"
[  178.496471] ){++++.+}
[  178.496599] , at:
[  178.496921] [<ffffffffa70ac206>] flush_work+0x1a6/0x2d0
[  178.497670]
               but task is already holding lock:
[  178.498499]  (
[  178.498724] "nvme-wq"
[  178.499074] ){++++.+}
[  178.499202] , at:
[  178.499520] [<ffffffffa70ad6c2>] process_one_work+0x162/0x6a0
[  178.500343]
               other info that might help us debug this:
[  178.501269]  Possible unsafe locking scenario:

[  178.502113]        CPU0
[  178.502472]        ----
[  178.502829]   lock(
[  178.503115] "nvme-wq"
[  178.503467] );
[  178.503716]   lock(
[  178.504001] "nvme-wq"
[  178.504353] );
[  178.504601]
                *** DEADLOCK ***

[  178.505441]  May be due to missing lock nesting notation

[  178.506453] 2 locks held by kworker/5:1/135:
[  178.507068]  #0:
[  178.507330]  (
[  178.507598] "nvme-wq"
[  178.507726] ){++++.+}
[  178.508079] , at:
[  178.508173] [<ffffffffa70ad6c2>] process_one_work+0x162/0x6a0
[  178.509004]  #1:
[  178.509265]  (
[  178.509532] (&ctrl->delete_work)
[  178.509795] ){+.+.+.}
[  178.510145] , at:
[  178.510239] [<ffffffffa70ad6c2>] process_one_work+0x162/0x6a0
[  178.511070]
               stack backtrace:
:
[  178.511693] CPU: 5 PID: 135 Comm: kworker/5:1 Tainted: G           OE   4.9.0-rc4-c844263313a8-lb #3
[  178.512974] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.1-1ubuntu1 04/01/2014
[  178.514247] Workqueue: nvme-wq nvme_del_ctrl_work [nvme_tcp]
[  178.515071]  ffffc2668175bae0 ffffffffa7450823 ffffffffa88abd80 ffffffffa88abd80
[  178.516195]  ffffc2668175bb98 ffffffffa70eb012 ffffffffa8d8d90d ffff9c472e9ea700
[  178.517318]  ffff9c472e9ea700 ffff9c4700000000 ffff9c4700007200 ab83be61bec0d50e
[  178.518443] Call Trace:
[  178.518807]  [<ffffffffa7450823>] dump_stack+0x85/0xc2
[  178.519542]  [<ffffffffa70eb012>] __lock_acquire+0x17d2/0x18f0
[  178.520377]  [<ffffffffa75839a7>] ? serial8250_console_putchar+0x27/0x30
[  178.521330]  [<ffffffffa7583980>] ? wait_for_xmitr+0xa0/0xa0
[  178.522174]  [<ffffffffa70ac1eb>] ? flush_work+0x18b/0x2d0
[  178.522975]  [<ffffffffa70eb7cb>] lock_acquire+0x11b/0x220
[  178.523753]  [<ffffffffa70ac206>] ? flush_work+0x1a6/0x2d0
[  178.524535]  [<ffffffffa70ac229>] flush_work+0x1c9/0x2d0
[  178.525291]  [<ffffffffa70ac206>] ? flush_work+0x1a6/0x2d0
[  178.526077]  [<ffffffffa70a9cf0>] ? flush_workqueue_prep_pwqs+0x220/0x220
[  178.527040]  [<ffffffffa70ae7cf>] __cancel_work_timer+0x10f/0x1d0
[  178.527907]  [<ffffffffa70fecb9>] ? vprintk_default+0x29/0x40
[  178.528726]  [<ffffffffa71cb507>] ? printk+0x48/0x50
[  178.529434]  [<ffffffffa70ae8c3>] cancel_delayed_work_sync+0x13/0x20
[  178.530381]  [<ffffffffc042100b>] nvme_stop_ctrl+0x5b/0x70 [nvme_core]
[  178.531314]  [<ffffffffc0403dcc>] nvme_del_ctrl_work+0x2c/0x50 [nvme_tcp]
[  178.532271]  [<ffffffffa70ad741>] process_one_work+0x1e1/0x6a0
[  178.533101]  [<ffffffffa70ad6c2>] ? process_one_work+0x162/0x6a0
[  178.533954]  [<ffffffffa70adc4e>] worker_thread+0x4e/0x490
[  178.534735]  [<ffffffffa70adc00>] ? process_one_work+0x6a0/0x6a0
[  178.535588]  [<ffffffffa70adc00>] ? process_one_work+0x6a0/0x6a0
[  178.536441]  [<ffffffffa70b48cf>] kthread+0xff/0x120
[  178.537149]  [<ffffffffa70b47d0>] ? kthread_park+0x60/0x60
[  178.538094]  [<ffffffffa70b47d0>] ? kthread_park+0x60/0x60
[  178.538900]  [<ffffffffa78e332a>] ret_from_fork+0x2a/0x40
Signed-off-by: NRoy Shterman <roys@lightbitslabs.com>
Signed-off-by: NSagi Grimberg <sagi@grimberg.me>
Signed-off-by: NChristoph Hellwig <hch@lst.de>

drivers/nvme/host/core.c

@@ -65,9 +65,26 @@ static bool streams;
 module_param(streams, bool, 0644);
 MODULE_PARM_DESC(streams, "turn on support for Streams write directives");
 
+/*
+ * nvme_wq - hosts nvme related works that are not reset or delete
+ * nvme_reset_wq - hosts nvme reset works
+ * nvme_delete_wq - hosts nvme delete works
+ *
+ * nvme_wq will host works such are scan, aen handling, fw activation,
+ * keep-alive error recovery, periodic reconnects etc. nvme_reset_wq
+ * runs reset works which also flush works hosted on nvme_wq for
+ * serialization purposes. nvme_delete_wq host controller deletion
+ * works which flush reset works for serialization.
+ */
 struct workqueue_struct *nvme_wq;
 EXPORT_SYMBOL_GPL(nvme_wq);
 
+struct workqueue_struct *nvme_reset_wq;
+EXPORT_SYMBOL_GPL(nvme_reset_wq);
+
+struct workqueue_struct *nvme_delete_wq;
+EXPORT_SYMBOL_GPL(nvme_delete_wq);
+
 static DEFINE_IDA(nvme_subsystems_ida);
 static LIST_HEAD(nvme_subsystems);
 static DEFINE_MUTEX(nvme_subsystems_lock);
@@ -89,7 +106,7 @@ int nvme_reset_ctrl(struct nvme_ctrl *ctrl)
 {
 	if (!nvme_change_ctrl_state(ctrl, NVME_CTRL_RESETTING))
 		return -EBUSY;
-	if (!queue_work(nvme_wq, &ctrl->reset_work))
+	if (!queue_work(nvme_reset_wq, &ctrl->reset_work))
 		return -EBUSY;
 	return 0;
 }
@@ -123,7 +140,7 @@ int nvme_delete_ctrl(struct nvme_ctrl *ctrl)
 {
 	if (!nvme_change_ctrl_state(ctrl, NVME_CTRL_DELETING))
 		return -EBUSY;
-	if (!queue_work(nvme_wq, &ctrl->delete_work))
+	if (!queue_work(nvme_delete_wq, &ctrl->delete_work))
 		return -EBUSY;
 	return 0;
 }
@@ -3526,16 +3543,26 @@ EXPORT_SYMBOL_GPL(nvme_reinit_tagset);
 
 int __init nvme_core_init(void)
 {
-	int result;
+	int result = -ENOMEM;
 
 	nvme_wq = alloc_workqueue("nvme-wq",
 			WQ_UNBOUND | WQ_MEM_RECLAIM | WQ_SYSFS, 0);
 	if (!nvme_wq)
-		return -ENOMEM;
+		goto out;
+
+	nvme_reset_wq = alloc_workqueue("nvme-reset-wq",
+			WQ_UNBOUND | WQ_MEM_RECLAIM | WQ_SYSFS, 0);
+	if (!nvme_reset_wq)
+		goto destroy_wq;
+
+	nvme_delete_wq = alloc_workqueue("nvme-delete-wq",
+			WQ_UNBOUND | WQ_MEM_RECLAIM | WQ_SYSFS, 0);
+	if (!nvme_delete_wq)
+		goto destroy_reset_wq;
 
 	result = alloc_chrdev_region(&nvme_chr_devt, 0, NVME_MINORS, "nvme");
 	if (result < 0)
-		goto destroy_wq;
+		goto destroy_delete_wq;
 
 	nvme_class = class_create(THIS_MODULE, "nvme");
 	if (IS_ERR(nvme_class)) {
@@ -3554,8 +3581,13 @@ int __init nvme_core_init(void)
 	class_destroy(nvme_class);
 unregister_chrdev:
 	unregister_chrdev_region(nvme_chr_devt, NVME_MINORS);
+destroy_delete_wq:
+	destroy_workqueue(nvme_delete_wq);
+destroy_reset_wq:
+	destroy_workqueue(nvme_reset_wq);
 destroy_wq:
 	destroy_workqueue(nvme_wq);
+out:
 	return result;
 }
 
@@ -3565,6 +3597,8 @@ void nvme_core_exit(void)
 	class_destroy(nvme_subsys_class);
 	class_destroy(nvme_class);
 	unregister_chrdev_region(nvme_chr_devt, NVME_MINORS);
+	destroy_workqueue(nvme_delete_wq);
+	destroy_workqueue(nvme_reset_wq);
 	destroy_workqueue(nvme_wq);
 }
 

drivers/nvme/host/nvme.h

@@ -32,6 +32,8 @@ extern unsigned int admin_timeout;
 #define NVME_KATO_GRACE		10
 
 extern struct workqueue_struct *nvme_wq;
+extern struct workqueue_struct *nvme_reset_wq;
+extern struct workqueue_struct *nvme_delete_wq;
 
 enum {
 	NVME_NS_LBA		= 0,

drivers/nvme/host/rdma.c

@@ -2029,7 +2029,7 @@ static void nvme_rdma_remove_one(struct ib_device *ib_device, void *client_data)
 	}
 	mutex_unlock(&nvme_rdma_ctrl_mutex);
 
-	flush_workqueue(nvme_wq);
+	flush_workqueue(nvme_delete_wq);
 }
 
 static struct ib_client nvme_rdma_ib_client = {

drivers/nvme/target/loop.c

@@ -717,7 +717,7 @@ static void __exit nvme_loop_cleanup_module(void)
 		nvme_delete_ctrl(&ctrl->ctrl);
 	mutex_unlock(&nvme_loop_ctrl_mutex);
 
-	flush_workqueue(nvme_wq);
+	flush_workqueue(nvme_delete_wq);
 }
 
 module_init(nvme_loop_init_module);