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

Luis Henriques
2024-07-24T13:38:56Z

On Wed, Jul 24 2024, Jan Kara wrote:

> 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!

Sure, both suggestions make sense. I'll update the patches for v2.

Cheers,
--
Luís

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