linux-kernel - Re: [PATCH 2/4] AFS: Add a function to excise a rejected write from the pagecache

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Date:	Thu, 24 May 2007 23:34:33 +0100
From:	David Howells <dhowells@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] AFS: Add a function to excise a rejected write from the pagecache

Andrew Morton <akpm@...ux-foundation.org> wrote:

> So my reason for asking the above is to try to find a way to make all these
> new PG-error games just go away.

Yeah.  However, there needs to be something to cover the gap between releasing
PG_writeback and getting PG_lock.  They have to be done in that order to avoid
deadlocking against truncate and other stuff, but that leaves a window in which
the page appears to be in a good state - one in which prepare_write() or
page_mkwrite() can potentially leak through.

Nick Piggin talked about using an extra lock, but as far as I can tell, that
just compounds the deadlock problems.

I suppose I could leave something in page->private that indicated that the
page was defunct, but that'd have to be done by the filesystem, probably
before calling cancel_rejected_write().

David
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