btrfs: remove no longer necessary chunk mutex locking cases

Initially when the 'removed' flag was added to a block group to avoid
races between block group removal and fitrim, by commit 04216820
("Btrfs: fix race between fs trimming and block group remove/allocation"),
we had to lock the chunks mutex because we could be moving the block
group from its current list, the pending chunks list, into the pinned
chunks list, or we could just be adding it to the pinned chunks if it was
not in the pending chunks list. Both lists were protected by the chunk
mutex.

However we no longer have those lists since commit 1c11b63e
("btrfs: replace pending/pinned chunks lists with io tree"), and locking
the chunk mutex is no longer necessary because of that. The same happens
at btrfs_unfreeze_block_group(), we lock the chunk mutex because the block
group's extent map could be part of the pinned chunks list and the call
to remove_extent_mapping() could be deleting it from that list, which
used to be protected by that mutex.

So just remove those lock and unlock calls as they are not needed anymore.
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/block-group.c

@@ -1111,7 +1111,6 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
 	if (ret < 0)
 		goto out;
 
-	mutex_lock(&fs_info->chunk_mutex);
 	spin_lock(&block_group->lock);
 	block_group->removed = 1;
 	/*
@@ -1143,8 +1142,6 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
 	remove_em = (atomic_read(&block_group->frozen) == 0);
 	spin_unlock(&block_group->lock);
 
-	mutex_unlock(&fs_info->chunk_mutex);
-
 	if (remove_em) {
 		struct extent_map_tree *em_tree;
 
@@ -3437,7 +3434,6 @@ void btrfs_unfreeze_block_group(struct btrfs_block_group *block_group)
 	spin_unlock(&block_group->lock);
 
 	if (cleanup) {
-		mutex_lock(&fs_info->chunk_mutex);
 		em_tree = &fs_info->mapping_tree;
 		write_lock(&em_tree->lock);
 		em = lookup_extent_mapping(em_tree, block_group->start,
@@ -3445,7 +3441,6 @@ void btrfs_unfreeze_block_group(struct btrfs_block_group *block_group)
 		BUG_ON(!em); /* logic error, can't happen */
 		remove_extent_mapping(em_tree, em);
 		write_unlock(&em_tree->lock);
-		mutex_unlock(&fs_info->chunk_mutex);
 
 		/* once for us and once for the tree */
 		free_extent_map(em);