On Thu 04-10-18 08:44:02, Greg KH wrote:
> On Thu, Oct 04, 2018 at 12:46:40PM +0200, Jan Kara wrote:
> > The code cleaning transaction's lists of checkpoint buffers has a bug
> > where it increases bh refcount only after releasing
> > journal->j_list_lock. Thus the following race is possible:
> >
> > CPU0 CPU1
> > jbd2_log_do_checkpoint()
> > jbd2_journal_try_to_free_buffers()
> > __journal_try_to_free_buffer(bh)
> > ...
> > while (transaction->t_checkpoint_io_list)
> > ...
> > if (buffer_locked(bh)) {
> >
> > <-- IO completes now, buffer gets unlocked -->
> >
> > spin_unlock(&journal->j_list_lock);
> > spin_lock(&journal->j_list_lock);
> > __jbd2_journal_remove_checkpoint(jh);
> > spin_unlock(&journal->j_list_lock);
> > try_to_free_buffers(page);
> > get_bh(bh) <-- accesses freed bh
> >
> > Fix the problem by grabbing bh reference before unlocking
> > journal->j_list_lock.
> >
> > Fixes: dc6e8d669cf5cb3ff84707c372c0a2a8a5e80845
> > Fixes: be1158cc615fd723552f0d9912087423c7cadda5
>
> Nit, this normally looks like:
>
> Fixes: dc6e8d669cf5 ("jbd2: don't call get_bh() before calling __jbd2_journal_remove_checkpoint()")
>
> And this is created by:
> git show -s --abbrev-commit --abbrev=12 --pretty=format:"%h (\"%s\")%n"
OK, ok, will do next time. The full git commit ID is faster to cut-n-paste
which shows how lazy I'm ;)
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
