Re: [PATCH] btrfs: fix a possible umount deadlock

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On 09/09/2016 08:53 PM, David Sterba wrote:
On Fri, Sep 09, 2016 at 04:31:04PM +0800, Anand Jain wrote:
 static int __btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
 {
 	struct btrfs_device *device, *tmp;
+	static LIST_HEAD(pending_put);

Why is it static?

 sorry my mistake its typo. v2 is sent out.

Thanks, Anand


+	INIT_LIST_HEAD(&pending_put);

 	if (--fs_devices->opened > 0)
 		return 0;
@@ -906,9 +904,24 @@ static int __btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
 	mutex_lock(&fs_devices->device_list_mutex);
 	list_for_each_entry_safe(device, tmp, &fs_devices->devices, dev_list) {
 		btrfs_close_one_device(device);
+		list_add(&device->dev_list, &pending_put);
 	}
 	mutex_unlock(&fs_devices->device_list_mutex);

+	/*
+	 * btrfs_show_devname() is using the device_list_mutex,
+	 * sometimes a call to blkdev_put() leads vfs calling
+	 * into this func. So do put outside of device_list_mutex,
+	 * as of now.
+	 */
+	while (!list_empty(&pending_put)) {
+		device = list_entry(pending_put.next,
+					struct btrfs_device, dev_list);
+		list_del(&device->dev_list);
+		btrfs_close_bdev(device);
+		call_rcu(&device->rcu, free_device);
+	}
+
 	WARN_ON(fs_devices->open_devices);
 	WARN_ON(fs_devices->rw_devices);
 	fs_devices->opened = 0;
--
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