linux-kernel - Re: [PATCH] bcachefs: WARNING in bch2_fs_journal

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Message-ID: <e2oi7a4jj4gjhzcp66rygr5d6wqlock6c5jvuwszxuej3hldmd@tnvbf45nbx2x>
Date: Thu, 18 Jul 2024 17:24:11 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Camila Alvarez <cam.alvarez.i@...il.com>
Cc: syzbot+4093905737cf289b6b38@...kaller.appspotmail.com, 
	Brian Foster <bfoster@...hat.com>, linux-bcachefs@...r.kernel.org, linux-kernel@...r.kernel.org, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] bcachefs: WARNING in bch2_fs_journal_stop

On Wed, Jul 17, 2024 at 06:02:39PM GMT, Camila Alvarez wrote:
> last_seq and last_empty_seq suffered from an off by one error when the
> journal has no entries.
> 
> The indexes were fixed and an assertion is added to check that the
> last_empty_seq is always kept under the next valid seq number.

oh nice. I'm going to need to stare at this some more, I still feel like
this code needs to be clearer and less fiddly.

> 
> Reported-by: syzbot+4093905737cf289b6b38@...kaller.appspotmail.com
> Signed-off-by: Camila Alvarez <cam.alvarez.i@...il.com>
> ---
>  fs/bcachefs/journal.c | 23 +++++++++++++----------
>  1 file changed, 13 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/bcachefs/journal.c b/fs/bcachefs/journal.c
> index 10b19791ec98..7bbbf4b149e9 100644
> --- a/fs/bcachefs/journal.c
> +++ b/fs/bcachefs/journal.c
> @@ -1201,7 +1201,7 @@ int bch2_fs_journal_start(struct journal *j, u64 cur_seq)
>  	struct journal_replay *i, **_i;
>  	struct genradix_iter iter;
>  	bool had_entries = false;
> -	u64 last_seq = cur_seq, nr, seq;
> +        u64 last_written_seq = cur_seq - 1, last_seq = cur_seq - 1, nr, seq;
>  
>  	genradix_for_each_reverse(&c->journal_entries, iter, _i) {
>  		i = *_i;
> @@ -1209,11 +1209,11 @@ int bch2_fs_journal_start(struct journal *j, u64 cur_seq)
>  		if (journal_replay_ignore(i))
>  			continue;
>  
> -		last_seq = le64_to_cpu(i->j.last_seq);
> +		last_written_seq = le64_to_cpu(i->j.last_seq);
>  		break;
>  	}
>  
> -	nr = cur_seq - last_seq;
> +	nr = cur_seq - last_written_seq;
>  
>  	if (nr + 1 > j->pin.size) {
>  		free_fifo(&j->pin);
> @@ -1224,14 +1224,14 @@ int bch2_fs_journal_start(struct journal *j, u64 cur_seq)
>  		}
>  	}
>  
> -	j->replay_journal_seq	= last_seq;
> +	j->replay_journal_seq	= last_written_seq;
>  	j->replay_journal_seq_end = cur_seq;
> -	j->last_seq_ondisk	= last_seq;
> -	j->flushed_seq_ondisk	= cur_seq - 1;
> -	j->seq_ondisk		= cur_seq - 1;
> -	j->pin.front		= last_seq;
> +	j->last_seq_ondisk	= last_written_seq;
> +	j->flushed_seq_ondisk	= last_seq;
> +	j->seq_ondisk		= last_seq;
> +	j->pin.front		= last_written_seq;
>  	j->pin.back		= cur_seq;
> -	atomic64_set(&j->seq, cur_seq - 1);
> +	atomic64_set(&j->seq, last_seq);
>  
>  	fifo_for_each_entry_ptr(p, &j->pin, seq)
>  		journal_pin_list_init(p, 1);
> @@ -1261,7 +1261,10 @@ int bch2_fs_journal_start(struct journal *j, u64 cur_seq)
>  	}
>  
>  	if (!had_entries)
> -		j->last_empty_seq = cur_seq;
> +		j->last_empty_seq = last_seq;
> +
> +	WARN(j->last_empty_seq >= cur_seq, "journal startup error: last empty seq %llu is higher or equal than the next seq number to be used (%llu)",
> +	      j->last_empty_seq, cur_seq);
>  
>  	spin_lock(&j->lock);
>  
> -- 
> 2.34.1
>