linux-kernel - Re: [PATCH v2] bcachefs: fix last_seq and last_empty_seq in bch2_fs_journal

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Date: Mon, 27 May 2024 15:25:39 -0400 (-04)
From: Camila Alvarez Inostroza <cam.alvarez.i@...il.com>
To: Camila Alvarez <cam.alvarez.i@...il.com>
cc: Kent Overstreet <kent.overstreet@...ux.dev>, 
    Brian Foster <bfoster@...hat.com>, linux-bcachefs@...r.kernel.org, 
    linux-kernel@...r.kernel.org, 
    syzbot+10b936c5eaee2819b49b@...kaller.appspotmail.com
Subject: Re: [PATCH v2] bcachefs: fix last_seq and last_empty_seq in
 bch2_fs_journal_start()

Hello,
I was wondering if you had had the time to take a look at this.
Please let me know if there's something I'm missing.

Thanks!

On Sun, 19 May 2024, Camila Alvarez wrote:

> Values were left as the next possible sequence number when there were no
> entries.
>
> The fix involves updating the last_seq initial value and
> setting last_empty_seq to cur_seq - 1.
>
> Reported-by: syzbot+10b936c5eaee2819b49b@...kaller.appspotmail.com
> Signed-off-by: Camila Alvarez <cam.alvarez.i@...il.com>
> ---
> Changes in v2:
> - Introduce a new variable to distinguish the last sequence number, from
>  the last written sequence number
> - Abstract `cur_seq - 1` into a variable named `last_seq`
> - Reference to the last sequence number are changed from `cur_seq - 1`
>  to `last_seq`
> ---
> fs/bcachefs/journal.c | 22 +++++++++++-----------
> 1 file changed, 11 insertions(+), 11 deletions(-)
>
> diff --git a/fs/bcachefs/journal.c b/fs/bcachefs/journal.c
> index adec8e1ea73e..99fc32f0382d 100644
> --- a/fs/bcachefs/journal.c
> +++ b/fs/bcachefs/journal.c
> @@ -1195,8 +1195,8 @@ int bch2_fs_journal_start(struct journal *j, u64 cur_seq)
> 	struct journal_entry_pin_list *p;
> 	struct journal_replay *i, **_i;
> 	struct genradix_iter iter;
> -	bool had_entries = false;
> -	u64 last_seq = cur_seq, nr, seq;
> +	bool had_entries = false;
> +	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;
> @@ -1204,11 +1204,11 @@ 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);
> @@ -1219,14 +1219,14 @@ 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);
> @@ -1256,7 +1256,7 @@ 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;
>
> 	spin_lock(&j->lock);
>
> -- 
> 2.34.1
>
>