Re: [RFC PATCH 2/2] jbd2: reset fast commit offset only after fs cleanup is done

Jan Kara
2024-05-22T10:45:08Z

On Tue 21-05-24 16:45:35, Luis Henriques (SUSE) wrote:
> When doing a journal commit, the fast journal offset (journal->j_fc_off) is
> set to zero too early in the process. Since ext4 filesystem calls function
> jbd2_fc_release_bufs() in its j_fc_cleanup_callback (ext4_fc_cleanup()),
> that call will be a no-op exactly because the offset is zero.
>
> Move the fast commit offset further down in the journal commit code, until
> it's mostly done, immediately before clearing the on-going commit flags.
>
> Signed-off-by: Luis Henriques (SUSE) <luis.henriques@linux.dev>

Did you see any particular failure because of this? Because AFAICS the
buffers cleaned up by jbd2_fc_release_bufs() are only allocated during fast
commit (from ext4_fc_reserve_space()). And the code in
jbd2_journal_commit_transaction() is making sure fast commit isn't running
before we set journal->j_fc_off to 0.

Honza

> ---
> fs/jbd2/commit.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
> index 75ea4e9a5cab..88b834c7c9c9 100644
> --- a/fs/jbd2/commit.c
> +++ b/fs/jbd2/commit.c
> @@ -435,7 +435,6 @@ void jbd2_journal_commit_transaction(journal_t *journal)
> commit_transaction->t_tid);
>
> write_lock(&journal->j_state_lock);
> - journal->j_fc_off = 0;
> J_ASSERT(commit_transaction->t_state == T_RUNNING);
> commit_transaction->t_state = T_LOCKED;
>
> @@ -1133,6 +1132,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
> journal->j_commit_sequence, journal->j_tail_sequence);
>
> write_lock(&journal->j_state_lock);
> + journal->j_fc_off = 0;
> journal->j_flags &= ~JBD2_FULL_COMMIT_ONGOING;
> journal->j_flags &= ~JBD2_FAST_COMMIT_ONGOING;
> spin_lock(&journal->j_list_lock);
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR