Re: [PATCH v4] ext4: fix fast commit inode enqueueing during a full journal commit

["wangjianjian (C)" <wangjianjian3@huawei.com>]

On 2024/7/11 16:35, 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@linux.dev>
> ---
> Hi!
> 
> v4 of this patch enqueues the inode into STAGING *only* if the current tid
> is non-zero.  It will be zero when doing an fc commit, and this would mean
> to always re-enqueue the inode.  This fixes the regressions caught by Ted
> in v3 with fstests generic/472 generic/496 generic/643.
> 
> Also, since 2nd patch of v3 has already been merged, I've rebased this patch
> to be applied on top of it.
> 
>   fs/ext4/fast_commit.c | 10 ++++++++++
>   1 file changed, 10 insertions(+)
> 
> diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
> index 3926a05eceee..facbc8dbbaa2 100644
> --- a/fs/ext4/fast_commit.c
> +++ b/fs/ext4/fast_commit.c
> @@ -1290,6 +1290,16 @@ static void ext4_fc_cleanup(journal_t *journal, int full, tid_t tid)
>   				       EXT4_STATE_FC_COMMITTING);
>   		if (tid_geq(tid, iter->i_sync_tid))
>   			ext4_fc_reset_inode(&iter->vfs_inode);
> +		} else if (tid) {
> +			/*
> +			 * If the tid is valid (i.e. non-zero) re-enqueue the
one quick question about tid, if one disk is using long time and its tid 
  get wrapped to 0, is it a valid seq? I don't find code handling this 
situation.
> +			 * inode into STAGING, which will then be splice back
> +			 * into MAIN
> +			 */
> +			list_add_tail(&EXT4_I(&iter->vfs_inode)->i_fc_list,
> +				      &sbi->s_fc_q[FC_Q_STAGING]);
> +		}
> +
>   		/* Make sure EXT4_STATE_FC_COMMITTING bit is clear */
>   		smp_mb();
>   #if (BITS_PER_LONG < 64)
> 
-- 
Regards