jbd2: fix data missing when reusing bh which is ready to be checkpointed
authorZhihao Cheng <chengzhihao1@huawei.com>
Tue, 10 Jan 2023 01:53:27 +0000 (09:53 +0800)
committerTheodore Ts'o <tytso@mit.edu>
Sun, 19 Feb 2023 05:09:59 +0000 (00:09 -0500)
commite6b9bd7290d334451ce054e98e752abc055e0034
tree896b2a1ef4b8f83cdbe08dfd0980721cab4e476a
parent3039d8b8692408438a618fac2776b629852663c3
jbd2: fix data missing when reusing bh which is ready to be checkpointed

Following process will make data lost and could lead to a filesystem
corrupted problem:

1. jh(bh) is inserted into T1->t_checkpoint_list, bh is dirty, and
   jh->b_transaction = NULL
2. T1 is added into journal->j_checkpoint_transactions.
3. Get bh prepare to write while doing checkpoing:
           PA     PB
   do_get_write_access             jbd2_log_do_checkpoint
    spin_lock(&jh->b_state_lock)
     if (buffer_dirty(bh))
      clear_buffer_dirty(bh)   // clear buffer dirty
       set_buffer_jbddirty(bh)
    transaction =
    journal->j_checkpoint_transactions
    jh = transaction->t_checkpoint_list
    if (!buffer_dirty(bh))
                      __jbd2_journal_remove_checkpoint(jh)
      // bh won't be flushed
                    jbd2_cleanup_journal_tail
    __jbd2_journal_file_buffer(jh, transaction, BJ_Reserved)
4. Aborting journal/Power-cut before writing latest bh on journal area.

In this way we get a corrupted filesystem with bh's data lost.

Fix it by moving the clearing of buffer_dirty bit just before the call
to __jbd2_journal_file_buffer(), both bit clearing and jh->b_transaction
assignment are under journal->j_list_lock locked, so that
jbd2_log_do_checkpoint() will wait until jh's new transaction fininshed
even bh is currently not dirty. And journal_shrink_one_cp_list() won't
remove jh from checkpoint list if the buffer head is reused in
do_get_write_access().

Fetch a reproducer in [Link].

Link: https://bugzilla.kernel.org/show_bug.cgi?id=216898
Cc: <stable@kernel.org>
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: zhanchengbin <zhanchengbin1@huawei.com>
Suggested-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20230110015327.1181863-1-chengzhihao1@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
fs/jbd2/transaction.c