On Wed 17-07-24 18:22:20, 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 when doing a full commit. However,
> to prevent a race with a fast-commit, the clean-up callback has to be called
> with the journal locked.
>
> 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.
>
> Suggested-by: Jan Kara <jack@xxxxxxx>
> Signed-off-by: Luis Henriques (SUSE) <luis.henriques@xxxxxxxxx>
Looks good to me. Feel free to add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> Hi!
>
> And here's another attempt to fix this bug. The most significant change is
> that now it doesn't assume a 'special' meaning for a tid of '0'. Which is
> a wrong assumption as Jan has shown.
>
> I've also added a Suggested-by: tag, although Jan pretty much owns this
> patch -- I have simply tested it and sent it out!
>
> fs/ext4/fast_commit.c | 15 ++++++++++++++-
> fs/jbd2/journal.c | 2 +-
> 2 files changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
> index 3926a05eceee..df71fd5b1fed 100644
> --- a/fs/ext4/fast_commit.c
> +++ b/fs/ext4/fast_commit.c
> @@ -1288,8 +1288,21 @@ 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 (tid_geq(tid, iter->i_sync_tid))
> + if (tid_geq(tid, iter->i_sync_tid)) {
> ext4_fc_reset_inode(&iter->vfs_inode);
> + } else if (full) {
> + /*
> + * We are called after a full commit, inode has been
> + * modified while the commit was running. Re-enqueue
> + * the inode into STAGING, which will then be splice
> + * back into MAIN. This cannot happen during
> + * fastcommit because the journal is locked all the
> + * time in that case (and tid doesn't increase so
> + * tid check above isn't reliable).
> + */
> + 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)
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index 1ebf2393bfb7..291a431f8aaf 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -740,9 +740,9 @@ EXPORT_SYMBOL(jbd2_fc_begin_commit);
> */
> static int __jbd2_fc_end_commit(journal_t *journal, tid_t tid, bool fallback)
> {
> - jbd2_journal_unlock_updates(journal);
> if (journal->j_fc_cleanup_callback)
> journal->j_fc_cleanup_callback(journal, 0, tid);
> + jbd2_journal_unlock_updates(journal);
> write_lock(&journal->j_state_lock);
> journal->j_flags &= ~JBD2_FAST_COMMIT_ONGOING;
> if (fallback)
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
