Re: [PATCH 3/4] ext4: fix incorrect tid assumption in jbd2_journal_shrink_checkpoint_list()

Jan Kara
2024-07-24T09:30:04Z

On Tue 23-07-24 16:44:01, Luis Henriques (SUSE) wrote:
> Function jbd2_journal_shrink_checkpoint_list() assumes that '0' is not a
> valid value for transaction IDs, which is incorrect. Don't assume that and
> use two extra boolean variables to control the loop iterations and keep
> track of the first and last tid.
>
> Signed-off-by: Luis Henriques (SUSE) <luis.henriques@linux.dev>
> ---
> fs/jbd2/checkpoint.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
> index 77bc522e6821..f5a594237b7a 100644
> --- a/fs/jbd2/checkpoint.c
> +++ b/fs/jbd2/checkpoint.c
> @@ -410,6 +410,7 @@ unsigned long jbd2_journal_shrink_checkpoint_list(journal_t *journal,
> tid_t tid = 0;
> unsigned long nr_freed = 0;
> unsigned long freed;
> + bool is_first = true, is_last = false;
>
> again:
> spin_lock(&journal->j_list_lock);
> @@ -429,8 +430,10 @@ unsigned long jbd2_journal_shrink_checkpoint_list(journal_t *journal,
> else
> transaction = journal->j_checkpoint_transactions;
>
> - if (!first_tid)
> + if (is_first) {
> first_tid = transaction->t_tid;
> + is_first = false;
> + }
> last_transaction = journal->j_checkpoint_transactions->t_cpprev;
> next_transaction = transaction;
> last_tid = last_transaction->t_tid;
> @@ -455,12 +458,13 @@ unsigned long jbd2_journal_shrink_checkpoint_list(journal_t *journal,
> } else {
> journal->j_shrink_transaction = NULL;
> next_tid = 0;
> + is_last = true;
> }
>
> spin_unlock(&journal->j_list_lock);
> cond_resched();
>
> - if (*nr_to_scan && next_tid)
> + if (*nr_to_scan && !is_last)

I'd make this:

if (*nr_to_scan && journal->j_shrink_transaction)
goto again;

and just remove is_last. Also we might rename is_first to first_set? At
least to me it would be more comprehensible. Thanks!

Honza

> goto again;
> out:
> trace_jbd2_shrink_checkpoint_list(journal, first_tid, tid, last_tid,
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR