Subject: Re: ide errors in 7-rc1-mm1 and later
From: Chris Mason <mason@suse.com>
To: Andrew Morton <akpm@osdl.org>
Cc: Bartlomiej Zolnierkiewicz <B.Zolnierkiewicz@elka.pw.edu.pl>, axboe@suse.de,
       edt@aei.ca, linux-kernel@vger.kernel.org
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Date: Wed, 09 Jun 2004 20:28:08 -0400
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On Wed, 2004-06-09 at 19:50, Andrew Morton wrote:
> Bartlomiej Zolnierkiewicz <B.Zolnierkiewicz@elka.pw.edu.pl> wrote:
> >
> > Does journal has checksum or some other protection against failure during
> > writing journal to a disk?  If not than it still can be screwed even with
> > ordered writes if we are unfortunate enough.  ;-)
> 
> A transaction is written to disk as two synchronous operations: write all
> the data, wait on it, write the single commit block, wait on that.
> 
> If the commit block were to hit disk before the data then we have a window
> in which poweroff+recovery would replay garbage into the filesystem.
> 
> So I think we have a bug in the current ext3 barrier implementation - we
> need a blk_issue_flush() before submitting the buffer_ordered commit block.

The IDE barriers are both a pre and post flush.  If the commit block is
ordered, before the commit block hits the disk we know all the blocks
previously submitted are also on disk.

-chris


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