linux-ext4 - Re: [RFC][PATCH] set_page_buffer_dirty should skip unmapped buffers

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Date:	Thu, 7 Sep 2006 22:48:08 +0200
From:	Jan Kara <jack@...e.cz>
To:	Badari Pulavarty <pbadari@...ibm.com>
Cc:	Andrew Morton <akpm@...l.org>,
	Anton Altaparmakov <aia21@....ac.uk>, sct@...hat.com,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [RFC][PATCH] set_page_buffer_dirty should skip unmapped buffers

  Hi,

> >   Ugh! Are you sure? For this path the buffer must be attached (only) to
> > the running transaction. But then how the commit code comes to it?
> > Somebody would have to even manage to refile the buffer from the
> > committing transaction to the running one while the buffer is in wbuf[].
> > Could you check whether someone does __journal_refile_buffer() on your
> > marked buffers, please? Or whether we move buffer to BJ_Locked list in
> > the write_out_data: loop? Thanks.
> > 
> > 							
> 
> I added more debug in __journal_refile_buffer() to see if the marked
> buffers are getting refiled. I am able to reproduce the problem,
> but I don't see any debug including my original prints. (It looks as 
> if none of my debug code exists) - its really confusing. 
> 
> I will keep looking and get back to you.
> 
> I may try Andrew's buffer debug patch - if I get desperate.
  Ho, hum, I think I see what is hapenning. I think we steal the buffer
from commit in journal_dirty_data() (called e.g. from ext3_writepage()).
There we also take care of writing out the buffer so it's mostly OK.
Except that the commit code still keeps the reference to the buffer in
wbuf[]. So the right solution along the lines of your one would be to
check that each buffer in wbuf[] is buffer_jbd(), belongs to the right
transaction and list and only in that case run submit_bh() on it...

								Honza
-- 
Jan Kara <jack@...e.cz>
SuSE CR Labs
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