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 11:50:32 +0200
From: Jan Kara <jack@...e.cz>
To: "Luis Henriques (SUSE)" <luis.henriques@...ux.dev>
Cc: Theodore Ts'o <tytso@....edu>, Andreas Dilger <adilger@...ger.ca>,
	Jan Kara <jack@...e.cz>,
	Harshad Shirwadkar <harshadshirwadkar@...il.com>,
	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

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