linux-ext4 - Re: Help required for Debugging JBD

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Message-ID: <BANLkTimps6FyqNNUXFg2D6iAkFkLrKORMg@mail.gmail.com>
Date:	Wed, 22 Jun 2011 22:29:28 +0300
From:	Amir Goldstein <amir73il@...il.com>
To:	Niraj Kulkarni <kulkarniniraj14@...il.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: Help required for Debugging JBD

On Wed, Jun 22, 2011 at 9:27 PM, Niraj Kulkarni
<kulkarniniraj14@...il.com> wrote:
> Hi,
>     Thanks for that SysRq tip. Now I am able to get some logs.
>
> From OOPS message, it showed an assertion failure on
>    J_ASSERT_JH(jh, jh->b_transaction == journal->j_committing_transaction);
>
> In my code, I've modified journal_commit_transaction such that it collects
> all buffer_head in a linked list, with their corresponding
> buffer numbers in other list.
>     I collect all buffers (data + metadata ) and push them all
> simultaneously and pass list of block numbers through a special ioctl call.
>
> The problem that I see in my code is that all buffers are handled in same
> way as all data buffers in original code. ie metadata buffers are
> getting unfiled instead of refiling.

I am not sure what you are saying, but it sounds bad.
data buffers and metadata buffers are handled very differently.

>
> I am attaching my patch. Please can you see and check if that indeed is
> problem here?
>

JBD is one complicated piece of work (to me), so even if I do find time
to review your patch, it's not going to be easy for me.

> Also what can be possible solution to it? separation of buffers in 2 list
> (data, metadata) and handling them separately?
>

Without looking at your patches, I have a lead for you.
Lookup the "Journal guided RAID resync" patches.
They do something similar to what you describe, for a different purpose,
but they also maintain a list of data blocks and yes, they deal with them
separately.
These patches have been already tested, so they used to be in good shape,
but are not uptodate.

Good luck,
Amir.

> (Being a kernel noob, my coding does not conform to any standard. So please
> point out any blunders I've committed in my patch)
>
> Thank You
> Niraj
>
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