Btrfs: make btrfs_rm_device() fail gracefully

If shrinking done as part of the online device removal fails add that
device back to the allocation list and increment the rw_devices counter.
This fixes two bugs:

1) we could have a perfectly good device out of alloc list for no good
reason;

2) in the btrfs consisting of two devices, failure in btrfs_rm_device()
could lead to a situation where it was impossible to remove any of the
devices because of the "unable to remove the only writeable device"
error.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 9 insertions, 2 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index dadaaa8005c8..f31c33119bb6 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1337,11 +1337,11 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path)
 
         ret = btrfs_shrink_device(device, 0);
         if (ret)
-                goto error_brelse;
+                goto error_undo;
 
         ret = btrfs_rm_dev_item(root->fs_info->chunk_root, device);
         if (ret)
-                goto error_brelse;
+                goto error_undo;
 
         device->in_fs_metadata = 0;
 
@@ -1415,6 +1415,13 @@ out:
         mutex_unlock(&root->fs_info->volume_mutex);
         mutex_unlock(&uuid_mutex);
         return ret;
+error_undo:
+        if (device->writeable) {
+                list_add(&device->dev_alloc_list,
+                         &root->fs_info->fs_devices->alloc_list);
+                root->fs_info->fs_devices->rw_devices++;
+        }
+        goto error_brelse;
 }
 
 /*