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

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Message-ID: <000000000000bb836e0618888015@google.com>
Date: Wed, 15 May 2024 18:53:34 -0700
From: syzbot <syzbot+10b936c5eaee2819b49b@...kaller.appspotmail.com>
To: linux-kernel@...r.kernel.org
Subject: Re: [syzbot] [PATCH] bcachefs: fix last_seq and last_empty_seq in bch2_fs_journal_start()

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***

Subject: [PATCH] bcachefs: fix last_seq and last_empty_seq in bch2_fs_journal_start()
Author: cam.alvarez.i@...il.com

#syz test
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.

Signed-off-by: Camila Alvarez <cam.alvarez.i@...il.com>
---
 fs/bcachefs/journal.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/bcachefs/journal.c b/fs/bcachefs/journal.c
index adec8e1ea73e..3835c458eec9 100644
--- a/fs/bcachefs/journal.c
+++ b/fs/bcachefs/journal.c
@@ -1196,7 +1196,7 @@ 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_seq = cur_seq - 1, nr, seq;
 
 	genradix_for_each_reverse(&c->journal_entries, iter, _i) {
 		i = *_i;
@@ -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 = cur_seq - 1;
 
 	spin_lock(&j->lock);
 
-- 
2.34.1