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Commit 60376ce4 authored by Josef Bacik's avatar Josef Bacik Committed by Chris Mason
Browse files

Btrfs: fix race in sync and freeze again 



I screwed this up, there is a race between checking if there is a running
transaction and actually starting a transaction in sync where we could race
with a freezer and get ourselves into trouble.  To fix this we need to make
a new join type to only do the try lock on the freeze stuff.  If it fails
we'll return EPERM and just return from sync.  This fixes a hang Liu Bo
reported when running xfstest 68 in a loop.  Thanks,

Reported-by: default avatarLiu Bo <bo.li.liu@oracle.com>
Signed-off-by: default avatarJosef Bacik <jbacik@fusionio.com>
parent b3ae244e

fs/btrfs/super.c

+6 −9
Original line number Diff line number Diff line
@@ -854,16 +854,13 @@ int btrfs_sync_fs(struct super_block *sb, int wait) 


	btrfs_wait_ordered_extents(root, 0, 0);



	spin_lock(&fs_info->trans_lock);

	if (!fs_info->running_transaction) {

		spin_unlock(&fs_info->trans_lock);

	trans = btrfs_join_transaction_freeze(root);

	if (IS_ERR(trans)) {

		/* Frozen, don't bother */

		if (PTR_ERR(trans) == -EPERM)

			return 0;

	}

	spin_unlock(&fs_info->trans_lock);



	trans = btrfs_join_transaction(root);

	if (IS_ERR(trans))

		return PTR_ERR(trans);

	}

	return btrfs_commit_transaction(trans, root);

}

fs/btrfs/transaction.c

+11 −1
Original line number Diff line number Diff line
@@ -272,6 +272,7 @@ enum btrfs_trans_type { 
	TRANS_JOIN,

	TRANS_USERSPACE,

	TRANS_JOIN_NOLOCK,

	TRANS_JOIN_FREEZE,

};



static int may_wait_transaction(struct btrfs_root *root, int type)
@@ -341,7 +342,11 @@ 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 (type == TRANS_JOIN_FREEZE)

			return ERR_PTR(-EPERM);

		sb_start_intwrite(root->fs_info->sb);

	}



	if (may_wait_transaction(root, type))

		wait_current_trans(root);
@@ -424,6 +429,11 @@ struct btrfs_trans_handle *btrfs_start_ioctl_transaction(struct btrfs_root *root 
	return start_transaction(root, 0, TRANS_USERSPACE, 0);

}



struct btrfs_trans_handle *btrfs_join_transaction_freeze(struct btrfs_root *root)

{

	return start_transaction(root, 0, TRANS_JOIN_FREEZE, 0);

}



/* wait for a transaction commit to be fully complete */

static noinline void wait_for_commit(struct btrfs_root *root,

				    struct btrfs_transaction *commit)

fs/btrfs/transaction.h

+1 −0
Original line number Diff line number Diff line
@@ -102,6 +102,7 @@ struct btrfs_trans_handle *btrfs_start_transaction_noflush( 
					struct btrfs_root *root, int num_items);

struct btrfs_trans_handle *btrfs_join_transaction(struct btrfs_root *root);

struct btrfs_trans_handle *btrfs_join_transaction_nolock(struct btrfs_root *root);

struct btrfs_trans_handle *btrfs_join_transaction_freeze(struct btrfs_root *root);

struct btrfs_trans_handle *btrfs_start_ioctl_transaction(struct btrfs_root *root);

int btrfs_wait_for_commit(struct btrfs_root *root, u64 transid);

int btrfs_write_and_wait_transaction(struct btrfs_trans_handle *trans,