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

[Eunbong Song]

Hi, I just wonder. Is there no problem with endianess.
I mean usually bit field is defined with __BIG_ENDIAN_BITFIELD or
__LITTLE_ENDIAN_BITFIELD. But b_jlist and b_modfied is defined with no
pad.
It seems to be good but i just want to make sure.


Thanks.

2013/5/13 Dmitry Monakhov <dmonakhov@xxxxxxxxxx>:
> On Mon, 13 May 2013 19:26:34 +0800, Zheng Liu <gnehzuil.liu@xxxxxxxxx> wrote:
>> On Mon, May 13, 2013 at 09:53:25AM +0000, EUNBONG SONG wrote:
>> >
>> >
>> > > 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.
>>
>> Thanks for trying this patch.  Could you please repost the dmesg log for
>> me?  I want to make sure whether the second suspicious stuff causes this
>> regression or not.  Further, that would be great if you could try to
>> comment this line as the following?
> AFAIK  following assertion was triggered jh->b_transaction != NULL
>>
>> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
>> index 886ec2f..a9e3779 100644
>> --- a/fs/jbd2/journal.c
>> +++ b/fs/jbd2/journal.c
>> @@ -2453,7 +2453,7 @@ static void __journal_remove_journal_head(struct
>> buffer_head *bh)
>>         J_ASSERT_JH(jh, jh->b_transaction == NULL);
>>         J_ASSERT_JH(jh, jh->b_next_transaction == NULL);
>>         J_ASSERT_JH(jh, jh->b_cp_transaction == NULL);
>> -       J_ASSERT_JH(jh, jh->b_jlist == BJ_None);
>> +       /*J_ASSERT_JH(jh, jh->b_jlist == BJ_None);*/
>>         J_ASSERT_BH(bh, buffer_jbd(bh));
>>         J_ASSERT_BH(bh, jh2bh(jh) == bh);
>>         BUFFER_TRACE(bh, "remove journal_head");
>>
>> Really thanks,
>>                                                 - Zheng
>> --
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