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Commit 98114659 authored by Josef Bacik's avatar Josef Bacik Committed by Chris Mason
Browse files

Btrfs: fix race with freeze and free space inodes 



So we start our freeze, somebody comes in and does an fsync() on a file
where we have to commit a transaction for whatever reason, and we will
deadlock because the freeze is waiting on FS_FREEZE people to stop writing
to the file system, but the transaction is waiting for its free space inodes
to be written out, which are in turn waiting on sb_start_intwrite while
trying to write the file extents.  To fix this we'll just skip the
sb_start_intwrite() if we TRANS_JOIN_NOLOCK since we're being waited on by a
transaction commit so we're safe wrt to freeze and this will keep us from
deadlocking.  Thanks,

Signed-off-by: default avatarJosef Bacik <jbacik@fusionio.com>
parent 6bbe3a9c

fs/btrfs/transaction.c

+11 −2
Original line number Diff line number Diff line
@@ -342,7 +342,15 @@ static struct btrfs_trans_handle *start_transaction(struct btrfs_root *root, 
	if (!h)

		return ERR_PTR(-ENOMEM);



	if (!__sb_start_write(root->fs_info->sb, SB_FREEZE_FS, false)) {

	/*

	 * If we are JOIN_NOLOCK we're already committing a transaction and

	 * waiting on this guy, so we don't need to do the sb_start_intwrite

	 * because we're already holding a ref.  We need this because we could

	 * have raced in and did an fsync() on a file which can kick a commit

	 * and then we deadlock with somebody doing a freeze.

	 */

	if (type != TRANS_JOIN_NOLOCK &&

	    !__sb_start_write(root->fs_info->sb, SB_FREEZE_FS, false)) {

		if (type == TRANS_JOIN_FREEZE)

			return ERR_PTR(-EPERM);

		sb_start_intwrite(root->fs_info->sb);
@@ -601,6 +609,7 @@ static int __btrfs_end_transaction(struct btrfs_trans_handle *trans, 
		}

	}



	if (lock)

		sb_end_intwrite(root->fs_info->sb);



	WARN_ON(cur_trans != info->running_transaction);