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Date: Thu, 1 Jun 2006 23:41:58 +0200
From: Olaf Hering <olh@suse.de>
To: Andrew Morton <akpm@osdl.org>
Cc: linux-kernel@vger.kernel.org, viro@ftp.linux.org.uk
Subject: Re: [PATCH] cramfs corruption after BLKFLSBUF on loop device
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 On Thu, Jun 01, Andrew Morton wrote:

> Olaf Hering <olh@suse.de> wrote:
> >
> > 
> >  
> > +/* return a page in PageUptodate state, BLKFLSBUF may have flushed the page */
> > +static struct page *cramfs_read_cache_page(struct address_space *m, unsigned int n)
> > +{
> > +	struct page *page;
> > +	int readagain = 5;
> > +retry:
> > +	page = read_cache_page(m, n, (filler_t *)m->a_ops->readpage, NULL);
> > +	if (IS_ERR(page))
> > +		return NULL;
> > +	lock_page(page);
> > +	if (PageUptodate(page))
> > +		return page;
> > +	unlock_page(page);
> > +	page_cache_release(page);
> > +	if (readagain--)
> > +		goto retry;
> > +	return NULL;
> > +}
> 
> Better, but it's still awful, isn't it?  The things you were discussing
> with Chris look more promising.  PG_Dirty would be a bit of a hack, but at
> least it'd be a 100% reliable hack, whereas the above is a
> whatever-the-previous-failure-rate-was-to-the-fifth hack.

Do you want it like that?

lock_page(page);
if (PageUptodate(page)) {
        SetPageDirty(page);
        mb();
        return page;
}

and perhaps a ClearPageDirty() after memcpy.