btrfs: call btrfs_close_devices from ->kill_sb

Although btrfs is not yet implementing blk_holder_ops yet, there is a
requirement for a proper blk_holder_ops:

- blkdev_put() must not be called under sb->s_umount
  The blkdev_put()/bdev_fput() must not be called under sb->s_umount to
  avoid lock order reversal with disk->open_mutex.
  This is for the proper blk_holder_ops callbacks.

  Currently we're fine because we call regular fput() which defers the
  blk holder reclaiming.

To prepare for the future of blk_holder_ops, move the
btrfs_close_devices() calls into btrfs_free_fs_info().

That will be called from kill_sb() callbacks, which is also called for
error handing during mount failures, or there is already an existing
super block.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: Christoph Hellwig

fs/btrfs/disk-io.c

@@ -1246,6 +1246,8 @@ void btrfs_free_fs_info(struct btrfs_fs_info *fs_info)
 {
 	struct percpu_counter *em_counter = &fs_info->evictable_extent_maps;
 
+	if (fs_info->fs_devices)
+		btrfs_close_devices(fs_info->fs_devices);
 	percpu_counter_destroy(&fs_info->stats_read_blocks);
 	percpu_counter_destroy(&fs_info->dirty_metadata_bytes);
 	percpu_counter_destroy(&fs_info->delalloc_bytes);
@@ -3683,7 +3685,6 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
 
 	iput(fs_info->btree_inode);
 fail:
-	btrfs_close_devices(fs_info->fs_devices);
 	ASSERT(ret < 0);
 	return ret;
 }
@@ -4430,7 +4431,6 @@ void __cold close_ctree(struct btrfs_fs_info *fs_info)
 	iput(fs_info->btree_inode);
 
 	btrfs_mapping_tree_free(fs_info);
-	btrfs_close_devices(fs_info->fs_devices);
 }
 
 void btrfs_mark_buffer_dirty(struct btrfs_trans_handle *trans,

fs/btrfs/super.c

@@ -1869,18 +1869,14 @@ static int btrfs_get_tree_super(struct fs_context *fc)
 	if (ret)
 		return ret;
 
-	if (!(fc->sb_flags & SB_RDONLY) && fs_devices->rw_devices == 0) {
-		ret = -EACCES;
-		goto error;
-	}
+	if (!(fc->sb_flags & SB_RDONLY) && fs_devices->rw_devices == 0)
+		return -EACCES;
 
 	bdev = fs_devices->latest_dev->bdev;
 
 	sb = sget_fc(fc, btrfs_fc_test_super, set_anon_super_fc);
-	if (IS_ERR(sb)) {
-		ret = PTR_ERR(sb);
-		goto error;
-	}
+	if (IS_ERR(sb))
+		return PTR_ERR(sb);
 
 	set_device_specific_options(fs_info);
 
@@ -1889,17 +1885,15 @@ static int btrfs_get_tree_super(struct fs_context *fc)
 		 * Not the first mount of the fs thus got an existing super block.
 		 *
 		 * Will reuse the returned super block, fs_info and fs_devices.
-		 */
-		ASSERT(fc->s_fs_info == fs_info);
-
-		/*
+		 *
 		 * fc->s_fs_info is not touched and will be later freed by
 		 * put_fs_context() through btrfs_free_fs_context().
 		 *
-		 * But we have opened fs_devices at the beginning of the
-		 * function, thus still need to close them manually.
+		 * And the fs_info->fs_devices will also be closed by
+		 * btrfs_free_fs_context().
 		 */
-		btrfs_close_devices(fs_devices);
+		ASSERT(fc->s_fs_info == fs_info);
+
 		/*
 		 * At this stage we may have RO flag mismatch between
 		 * fc->sb_flags and sb->s_flags.  Caller should detect such
@@ -1928,10 +1922,6 @@ static int btrfs_get_tree_super(struct fs_context *fc)
 
 	fc->root = dget(sb->s_root);
 	return 0;
-
-error:
-	btrfs_close_devices(fs_devices);
-	return ret;
 }
 
 /*