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

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Message-ID: <6d42612b-1c20-0484-ce9f-eac509e6740d@macbook-pro-de-camila.local>
Date: Thu, 18 Jul 2024 18:42:55 -0400 (-04)
From: Camila Alvarez Inostroza <cam.alvarez.i@...il.com>
To: Kent Overstreet <kent.overstreet@...ux.dev>
cc: Camila Alvarez <cam.alvarez.i@...il.com>, 
    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 Thu, 18 Jul 2024, Kent Overstreet wrote:

> 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.
>
Sure! Please let me know if there's anything I can do to help.
>>
>> 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
>>
>