linux-kernel - Re: [PATCH v3 1/2] ext4: fix fast commit inode enqueueing during a full journal commit

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Date: Wed, 29 May 2024 09:52:15 -0700
From: harshad shirwadkar <harshadshirwadkar@...il.com>
To: Jan Kara <jack@...e.cz>
Cc: "Luis Henriques (SUSE)" <luis.henriques@...ux.dev>, "Theodore Ts'o" <tytso@....edu>, 
	Andreas Dilger <adilger@...ger.ca>, linux-ext4@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] ext4: fix fast commit inode enqueueing during a
 full journal commit

Looks good!

Reviewed-by: Harshad Shirwadkar <harshadshirwadkar@...il.com>


On Wed, May 29, 2024 at 2:50 AM Jan Kara <jack@...e.cz> wrote:
>
> On Wed 29-05-24 10:20:29, Luis Henriques (SUSE) wrote:
> > When a full journal commit is on-going, any fast commit has to be enqueued
> > into a different queue: FC_Q_STAGING instead of FC_Q_MAIN.  This enqueueing
> > is done only once, i.e. if an inode is already queued in a previous fast
> > commit entry it won't be enqueued again.  However, if a full commit starts
> > _after_ the inode is enqueued into FC_Q_MAIN, the next fast commit needs to
> > be done into FC_Q_STAGING.  And this is not being done in function
> > ext4_fc_track_template().
> >
> > This patch fixes the issue by re-enqueuing an inode into the STAGING queue
> > during the fast commit clean-up callback if it has a tid (i_sync_tid)
> > greater than the one being handled.  The STAGING queue will then be spliced
> > back into MAIN.
> >
> > This bug was found using fstest generic/047.  This test creates several 32k
> > bytes files, sync'ing each of them after it's creation, and then shutting
> > down the filesystem.  Some data may be loss in this operation; for example a
> > file may have it's size truncated to zero.
> >
> > Signed-off-by: Luis Henriques (SUSE) <luis.henriques@...ux.dev>
>
> Looks good to me! Feel free to add:
>
> Reviewed-by: Jan Kara <jack@...e.cz>
>
> Just a typo correction below.
>
> > diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
> > index 87c009e0c59a..088bd509b116 100644
> > --- a/fs/ext4/fast_commit.c
> > +++ b/fs/ext4/fast_commit.c
> > @@ -1282,8 +1282,17 @@ static void ext4_fc_cleanup(journal_t *journal, int full, tid_t tid)
> >               list_del_init(&iter->i_fc_list);
> >               ext4_clear_inode_state(&iter->vfs_inode,
> >                                      EXT4_STATE_FC_COMMITTING);
> > -             if (iter->i_sync_tid <= tid)
> > +             if (iter->i_sync_tid <= tid) {
> >                       ext4_fc_reset_inode(&iter->vfs_inode);
> > +             } else {
> > +                     /*
> > +                      * re-enqueue inode into STAGING, which later will be
> > +                      * splice back into MAIN
>                            ^^^ spliced
>
> > +                      */
> > +                     list_add_tail(&EXT4_I(&iter->vfs_inode)->i_fc_list,
> > +                                   &sbi->s_fc_q[FC_Q_STAGING]);
> > +             }
> > +
>
>                                                                 Honza
> --
> Jan Kara <jack@...e.com>
> SUSE Labs, CR