Commit 6822b3f7 authored by Filipe Manana's avatar Filipe Manana Committed by David Sterba
Browse files

btrfs: do not BUG_ON after failure to migrate space during truncation 



During truncation we reserve 2 metadata units when starting a transaction
(reserved space goes to fs_info->trans_block_rsv) and then attempt to
migrate 1 unit (min_size bytes) from fs_info->trans_block_rsv into the
local block reserve. If we ever fail we trigger a BUG_ON(), which should
never happen, because we reserved 2 units. However if we happen to fail
for some reason, we don't need to be so dire and hit a BUG_ON(), we can
just error out the truncation and, since this is highly unexpected,
surround the error check with WARN_ON(), to get an informative stack
trace and tag the branh as 'unlikely'. Also make the 'min_size' variable
const, since it's not supposed to ever change and any accidental change
could possibly make the space migration not so unlikely to fail.

Reviewed-by: default avatarQu Wenruo <wqu@suse.com>
Signed-off-by: default avatarFilipe Manana <fdmanana@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent df9f2782

fs/btrfs/inode.c

+18 −3
Original line number Diff line number Diff line
@@ -8344,7 +8344,7 @@ static int btrfs_truncate(struct btrfs_inode *inode, bool skip_writeback) 
	int ret;

	struct btrfs_trans_handle *trans;

	u64 mask = fs_info->sectorsize - 1;

	u64 min_size = btrfs_calc_metadata_size(fs_info, 1);

	const u64 min_size = btrfs_calc_metadata_size(fs_info, 1);



	if (!skip_writeback) {

		ret = btrfs_wait_ordered_range(&inode->vfs_inode,
@@ -8401,7 +8401,15 @@ static int btrfs_truncate(struct btrfs_inode *inode, bool skip_writeback) 
	/* Migrate the slack space for the truncate to our reserve */

	ret = btrfs_block_rsv_migrate(&fs_info->trans_block_rsv, rsv,

				      min_size, false);

	BUG_ON(ret);

	/*

	 * We have reserved 2 metadata units when we started the transaction and

	 * min_size matches 1 unit, so this should never fail, but if it does,

	 * it's not critical we just fail truncation.

	 */

	if (WARN_ON(ret)) {

		btrfs_end_transaction(trans);

		goto out;

	}



	trans->block_rsv = rsv;
@@ -8449,7 +8457,14 @@ static int btrfs_truncate(struct btrfs_inode *inode, bool skip_writeback) 
		btrfs_block_rsv_release(fs_info, rsv, -1, NULL);

		ret = btrfs_block_rsv_migrate(&fs_info->trans_block_rsv,

					      rsv, min_size, false);

		BUG_ON(ret);	/* shouldn't happen */

		/*

		 * We have reserved 2 metadata units when we started the

		 * transaction and min_size matches 1 unit, so this should never

		 * fail, but if it does, it's not critical we just fail truncation.

		 */

		if (WARN_ON(ret))

			break;



		trans->block_rsv = rsv;

	}