btrfs: close devices without offloading to a temporary list

Since commit 88c14590cdd6 ("btrfs: use RCU in btrfs_show_devname for
device list traversal") btrfs_show_devname no longer takes
device_list_mutex. As such the deadlock that 0ccd05285e7f ("btrfs: fix a
possible umount deadlock") aimed to fix no longer exists, we can free
the devices immediatelly and remove the code that does the pending work.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
[ update changelog ]
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index f7191fd..3c3359d 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1001,7 +1001,7 @@ static void btrfs_close_bdev(struct btrfs_device *device)
        blkdev_put(device->bdev, device->mode);
 }
 
-static void btrfs_prepare_close_one_device(struct btrfs_device *device)
+static void btrfs_close_one_device(struct btrfs_device *device)
 {
        struct btrfs_fs_devices *fs_devices = device->fs_devices;
        struct btrfs_device *new_device;
@@ -1019,6 +1019,8 @@ static void btrfs_prepare_close_one_device(struct btrfs_device *device)
        if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state))
                fs_devices->missing_devices--;
 
+       btrfs_close_bdev(device);
+
        new_device = btrfs_alloc_device(NULL, &device->devid,
                                        device->uuid);
        BUG_ON(IS_ERR(new_device)); /* -ENOMEM */
@@ -1032,39 +1034,23 @@ static void btrfs_prepare_close_one_device(struct btrfs_device *device)
 
        list_replace_rcu(&device->dev_list, &new_device->dev_list);
        new_device->fs_devices = device->fs_devices;
+
+       call_rcu(&device->rcu, free_device_rcu);
 }
 
 static int close_fs_devices(struct btrfs_fs_devices *fs_devices)
 {
        struct btrfs_device *device, *tmp;
-       struct list_head pending_put;
-
-       INIT_LIST_HEAD(&pending_put);
 
        if (--fs_devices->opened > 0)
                return 0;
 
        mutex_lock(&fs_devices->device_list_mutex);
        list_for_each_entry_safe(device, tmp, &fs_devices->devices, dev_list) {
-               btrfs_prepare_close_one_device(device);
-               list_add(&device->dev_list, &pending_put);
+               btrfs_close_one_device(device);
        }
        mutex_unlock(&fs_devices->device_list_mutex);
 
-       /*
-        * btrfs_show_devname() is using the device_list_mutex,
-        * sometimes 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_first_entry(&pending_put,
-                               struct btrfs_device, dev_list);
-               list_del(&device->dev_list);
-               btrfs_close_bdev(device);
-               call_rcu(&device->rcu, free_device_rcu);
-       }
-
        WARN_ON(fs_devices->open_devices);
        WARN_ON(fs_devices->rw_devices);
        fs_devices->opened = 0;