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"
thanks
greg k-h
