From: Jan Kara <jack@xxxxxxx> commit 3b1833e92baba135923af4a07e73fe6e54be5a2f upstream. Access to journal->j_running_transaction is not protected by appropriate lock and thus is racy. We are well aware of that and the code handles the race properly. Just add a comment and data_race() annotation. Cc: stable@xxxxxxxxxx Reported-by: syzbot+30774a6acf6a2cf6d535@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Jan Kara <jack@xxxxxxx> Link: https://lore.kernel.org/r/20210406161804.20150-1-jack@xxxxxxx Signed-off-by: Theodore Ts'o <tytso@xxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- fs/jbd2/transaction.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) --- a/fs/jbd2/transaction.c +++ b/fs/jbd2/transaction.c @@ -349,7 +349,12 @@ static int start_this_handle(journal_t * } alloc_transaction: - if (!journal->j_running_transaction) { + /* + * This check is racy but it is just an optimization of allocating new + * transaction early if there are high chances we'll need it. If we + * guess wrong, we'll retry or free unused transaction. + */ + if (!data_race(journal->j_running_transaction)) { /* * If __GFP_FS is not present, then we may be being called from * inside the fs writeback layer, so we MUST NOT fail.
