From: Bartlomiej Zolnierkiewicz <B.Zolnierkiewicz@elka.pw.edu.pl>
To: Andrew Morton <akpm@osdl.org>, Chris Mason <mason@suse.com>
Subject: Re: ide errors in 7-rc1-mm1 and later
Date: Thu, 10 Jun 2004 02:45:33 +0200
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On Thursday 10 of June 2004 02:38, Andrew Morton wrote:
> Chris Mason <mason@suse.com> wrote:
> > 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.
>
> Oh, OK.  Will the same apply to (for example) scsi?

Not OK.  Chris, pre and post flushes are for the same device.
Journal may be on different device than filesystem!


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