On Tue, Dec 19, 2017 at 7:44 AM, Qu Wenruo <wqu@xxxxxxxx> wrote:
> When multiple pending snapshots referring the same source subvolume are
> executed, enabled quota will cause root item corruption, where root
> items are using old bytenr (no backref in extent tree).
>
> This can be triggered by fstests btrfs/152.
>
> The cause is when source subvolume is still dirty, extra commit
> (simplied transaction commit) of qgroup_account_snapshot() can skip
> dirty roots not recorded in current transaction, making root item of
> source subvolume not updated.
>
> Fix it by forcing recording source subvolume in current transaction
> before qgroup sub-transaction commit.
>
> Reported-by: Justin Maggard <jmaggard@xxxxxxxxxxx>
> Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
Reviewed-by: Filipe Manana <fdmanana@xxxxxxxx>
Looks good.
> ---
> fs/btrfs/transaction.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
> index ddae813c01dd..f645e5de5fa5 100644
> --- a/fs/btrfs/transaction.c
> +++ b/fs/btrfs/transaction.c
> @@ -319,7 +319,7 @@ static int record_root_in_trans(struct btrfs_trans_handle *trans,
> if ((test_bit(BTRFS_ROOT_REF_COWS, &root->state) &&
> root->last_trans < trans->transid) || force) {
> WARN_ON(root == fs_info->extent_root);
> - WARN_ON(root->commit_root != root->node);
> + WARN_ON(!force && root->commit_root != root->node);
>
> /*
> * see below for IN_TRANS_SETUP usage rules
> @@ -1366,6 +1366,14 @@ static int qgroup_account_snapshot(struct btrfs_trans_handle *trans,
> if (!test_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags))
> return 0;
>
> + /*
> + * Ensure dirty @src will be commited.
> + * Or after comming commit_fs_roots() and switch_commit_roots(),
> + * any dirty but not recorded root will never be updated again.
> + * Causing outdated root item.
> + */
> + record_root_in_trans(trans, src, 1);
> +
> /*
> * We are going to commit transaction, see btrfs_commit_transaction()
> * comment for reason locking tree_log_mutex
> --
> 2.15.1
>
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--
Filipe David Manana,
“Whether you think you can, or you think you can't — you're right.”
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