Re: Re: Re: EXT4 panic at jbd2_journal_put_journal_head() in 3.9+

[EUNBONG SONG <eunb.song@samsung.com>]

> Hi all,

> First of all I couldn't reproduce this regression in my sand box.  So
> the following speculation is only my guess.  I suspect that the commit
> (ae4647fb) isn't root cause.  It just uncover a potential bug that has
> been there for a long time.  I look at the code, and found two
> suspicious stuff in jbd2.  The first one is in do_get_write_access().
> In this function we forgot to lock bh state when we check b_jlist ==
> BJ_Shadow.  I generate a patch to fix it, and I really think it is the
> root cause.  Further, in __journal_remove_journal_head() we check
> b_jlist == BJ_None.  But, when this function is called, bh state won't
> be locked sometimes.  So I suspect this is why we hit a BUG in
> jbd2_journal_put_journal_head().  But I don't have a good solution to
> fix this until now because I don't know whether we need to lock bh state
> here, or maybe we should remove this assertation.
>
> So, generally, Tony, Eunbong, could you please try the following patch?
>
> Thanks in advance,
>                                                 - Zheng


Hi, I tested your patch. Unfortunately, the same problem was reproduced.
Thanks.