Re: [PATCH] [RFC] Fix data missing when reusing bh which is ready to be checkpointed

[Zhihao Cheng]

在 2022/12/21 18:13, Jan Kara 写道:
> On Tue 20-12-22 23:05:51, Zhihao Cheng wrote:
> > From: zhanchengbin <zhanchengbin1@xxxxxxxxxx>
> >
> > 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.

[...]
> >   fs/jbd2/transaction.c | 8 ++++++--
> >   1 file changed, 6 insertions(+), 2 deletions(-)
>
> Good catch! Did you find it by code inspection or were you able to actually
> trigger this problem?

By code inspection.
Reproducer: https://bugzilla.kernel.org/show_bug.cgi?id=216898