Re: [PATCH 2/2] jbd2: flush filesystem device before updating tail sequence

[Kemeng Shi]

on 12/3/2024 9:44 AM, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@xxxxxxxxxx>
> 
> When committing transaction in jbd2_journal_commit_transaction(), the
> disk caches for the filesystem device should be flushed before updating
> the journal tail sequence. However, this step is missed if the journal
> is not located on the filesystem device. As a result, the filesystem may
> become inconsistent following a power failure or system crash. Fix it by
> ensuring that the filesystem device is flushed appropriately.
> 
> Fixes: 3339578f0578 ("jbd2: cleanup journal tail after transaction commit")
> Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
> ---
>  fs/jbd2/commit.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
> index 4305a1ac808a..f95cf272a1b5 100644
> --- a/fs/jbd2/commit.c
> +++ b/fs/jbd2/commit.c
> @@ -776,9 +776,9 @@ void jbd2_journal_commit_transaction(journal_t *journal)
>  	/*
>  	 * If the journal is not located on the file system device,
>  	 * then we must flush the file system device before we issue
> -	 * the commit record
> +	 * the commit record and update the journal tail sequence.
>  	 */
> -	if (commit_transaction->t_need_data_flush &&
> +	if ((commit_transaction->t_need_data_flush || update_tail) &&
>  	    (journal->j_fs_dev != journal->j_dev) &&
>  	    (journal->j_flags & JBD2_BARRIER))
>  		blkdev_issue_flush(journal->j_fs_dev);
> 
In journal_submit_commit_record(), we will submit commit block with REQ_PREFLUSH
which is supposed to ensure disk cache is flushed before writing commit block.
So I think the current code is fine.
Please correct me if I miss anything.

Thanks,
Kemeng