NVMe: Start-stop nvme_thread during device add-remove.

Done to ensure nvme_thread is not running when there
are no devices to poll.

Signed-off-by: Dan McLeran <daniel.mcleran@intel.com>
Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>

1 files changed, 42 insertions, 14 deletions

diff --git a/drivers/block/nvme-core.c b/drivers/block/nvme-core.c
index 7c57b1d955a1..2d69bfec95a4 100644
--- a/drivers/block/nvme-core.c
+++ b/drivers/block/nvme-core.c
@@ -64,6 +64,7 @@ static DEFINE_SPINLOCK(dev_list_lock);
 static LIST_HEAD(dev_list);
 static struct task_struct *nvme_thread;
 static struct workqueue_struct *nvme_workq;
+static wait_queue_head_t nvme_kthread_wait;
 
 static void nvme_reset_failed_dev(struct work_struct *ws);
 
@@ -2374,6 +2375,26 @@ static void nvme_disable_io_queues(struct nvme_dev *dev)
         kthread_stop(kworker_task);
 }
 
+/*
+* Remove the node from the device list and check
+* for whether or not we need to stop the nvme_thread.
+*/
+static void nvme_dev_list_remove(struct nvme_dev *dev)
+{
+        struct task_struct *tmp = NULL;
+
+        spin_lock(&dev_list_lock);
+        list_del_init(&dev->node);
+        if (list_empty(&dev_list) && !IS_ERR_OR_NULL(nvme_thread)) {
+                tmp = nvme_thread;
+                nvme_thread = NULL;
+        }
+        spin_unlock(&dev_list_lock);
+
+        if (tmp)
+                kthread_stop(tmp);
+}
+
 static void nvme_dev_shutdown(struct nvme_dev *dev)
 {
         int i;
@@ -2381,9 +2402,7 @@ static void nvme_dev_shutdown(struct nvme_dev *dev)
         dev->initialized = 0;
         unregister_hotcpu_notifier(&dev->nb);
 
-        spin_lock(&dev_list_lock);
-        list_del_init(&dev->node);
-        spin_unlock(&dev_list_lock);
+        nvme_dev_list_remove(dev);
 
         if (!dev->bar || (dev->bar && readl(&dev->bar->csts) == -1)) {
                 for (i = dev->queue_count - 1; i >= 0; i--) {
@@ -2524,6 +2543,7 @@ static const struct file_operations nvme_dev_fops = {
 static int nvme_dev_start(struct nvme_dev *dev)
 {
         int result;
+        bool start_thread = false;
 
         result = nvme_dev_map(dev);
         if (result)
@@ -2534,9 +2554,24 @@ static int nvme_dev_start(struct nvme_dev *dev)
                 goto unmap;
 
         spin_lock(&dev_list_lock);
+        if (list_empty(&dev_list) && IS_ERR_OR_NULL(nvme_thread)) {
+                start_thread = true;
+                nvme_thread = NULL;
+        }
         list_add(&dev->node, &dev_list);
         spin_unlock(&dev_list_lock);
 
+        if (start_thread) {
+                nvme_thread = kthread_run(nvme_kthread, NULL, "nvme");
+                wake_up(&nvme_kthread_wait);
+        } else
+                wait_event_killable(nvme_kthread_wait, nvme_thread);
+
+        if (IS_ERR_OR_NULL(nvme_thread)) {
+                result = nvme_thread ? PTR_ERR(nvme_thread) : -EINTR;
+                goto disable;
+        }
+
         result = nvme_setup_io_queues(dev);
         if (result && result != -EBUSY)
                 goto disable;
@@ -2545,9 +2580,7 @@ static int nvme_dev_start(struct nvme_dev *dev)
 
  disable:
         nvme_disable_queue(dev, 0);
-        spin_lock(&dev_list_lock);
-        list_del_init(&dev->node);
-        spin_unlock(&dev_list_lock);
+        nvme_dev_list_remove(dev);
  unmap:
         nvme_dev_unmap(dev);
         return result;
@@ -2776,14 +2809,11 @@ static int __init nvme_init(void)
 {
         int result;
 
-        nvme_thread = kthread_run(nvme_kthread, NULL, "nvme");
-        if (IS_ERR(nvme_thread))
-                return PTR_ERR(nvme_thread);
+        init_waitqueue_head(&nvme_kthread_wait);
 
-        result = -ENOMEM;
         nvme_workq = create_singlethread_workqueue("nvme");
         if (!nvme_workq)
-                goto kill_kthread;
+                return -ENOMEM;
 
         result = register_blkdev(nvme_major, "nvme");
         if (result < 0)
@@ -2800,8 +2830,6 @@ static int __init nvme_init(void)
         unregister_blkdev(nvme_major, "nvme");
  kill_workq:
         destroy_workqueue(nvme_workq);
- kill_kthread:
-        kthread_stop(nvme_thread);
         return result;
 }
 
@@ -2810,7 +2838,7 @@ static void __exit nvme_exit(void)
         pci_unregister_driver(&nvme_driver);
         unregister_blkdev(nvme_major, "nvme");
         destroy_workqueue(nvme_workq);
-        kthread_stop(nvme_thread);
+        BUG_ON(nvme_thread && !IS_ERR(nvme_thread));
 }
 
 MODULE_AUTHOR("Matthew Wilcox <willy@linux.intel.com>");