[PATCH v2] jbd2: allocate lock_class_key for jbd2_handle dynamically

Tetsuo Handa
2025-10-22T11:11:58Z

syzbot is reporting possibility of deadlock due to sharing lock_class_key
for jbd2_handle across ext4 and ocfs2. But this is a false positive, for
one disk partition can't have two filesystems at the same time.

Reported-by: syzbot+6e493c165d26d6fcbf72@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=6e493c165d26d6fcbf72
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Tested-by: syzbot+6e493c165d26d6fcbf72@syzkaller.appspotmail.com
---
fs/jbd2/journal.c | 6 ++++--
include/linux/jbd2.h | 6 ++++++
2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index d480b94117cd..f43474002f50 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1521,7 +1521,6 @@ static journal_t *journal_init_common(struct block_device *bdev,
struct block_device *fs_dev,
unsigned long long start, int len, int blocksize)
{
- static struct lock_class_key jbd2_trans_commit_key;
journal_t *journal;
int err;
int n;
@@ -1530,6 +1529,7 @@ static journal_t *journal_init_common(struct block_device *bdev,
if (!journal)
return ERR_PTR(-ENOMEM);

+ lockdep_register_key(&journal->jbd2_trans_commit_key);
journal->j_blocksize = blocksize;
journal->j_dev = bdev;
journal->j_fs_dev = fs_dev;
@@ -1560,7 +1560,7 @@ static journal_t *journal_init_common(struct block_device *bdev,
journal->j_max_batch_time = 15000; /* 15ms */
atomic_set(&journal->j_reserved_credits, 0);
lockdep_init_map(&journal->j_trans_commit_map, "jbd2_handle",
- &jbd2_trans_commit_key, 0);
+ &journal->jbd2_trans_commit_key, 0);

/* The journal is marked for error until we succeed with recovery! */
journal->j_flags = JBD2_ABORT;
@@ -1611,6 +1611,7 @@ static journal_t *journal_init_common(struct block_device *bdev,
kfree(journal->j_wbuf);
jbd2_journal_destroy_revoke(journal);
journal_fail_superblock(journal);
+ lockdep_unregister_key(&journal->jbd2_trans_commit_key);
kfree(journal);
return ERR_PTR(err);
}
@@ -2187,6 +2188,7 @@ int jbd2_journal_destroy(journal_t *journal)
jbd2_journal_destroy_revoke(journal);
kfree(journal->j_fc_wbuf);
kfree(journal->j_wbuf);
+ lockdep_unregister_key(&journal->jbd2_trans_commit_key);
kfree(journal);

return err;
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index 43b9297fe8a7..f5eaf76198f3 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -1253,6 +1253,12 @@ struct journal_s
*/
struct lockdep_map j_trans_commit_map;
#endif
+ /**
+ * @jbd2_trans_commit_key:
+ *
+ * "struct lock_class_key" for @j_trans_commit_map
+ */
+ struct lock_class_key jbd2_trans_commit_key;

/**
* @j_fc_cleanup_callback:
--
2.47.3