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+4093905737cf289b6...@syzkaller.appspotmail.com
> Signed-off-by: Camila Alvarez <cam.alvare...@gmail.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
>
