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

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Date:	Fri, 25 May 2007 00:08:43 +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:

> hm.  I don't see why that race window would be a problem in practice: the
> page-exciser does a lock_page();wait_on_page_writeback() as normal, then
> proceeds with its business?

No.  The page-exciser ends (cancels) PG_writeback, not waits for it (something
has to clear the flag).  The problem is that the truncation routines may be
sat there holding a lock on the page whilst waiting for PG_writeback to go
away - so we have to clear PG_writeback before we can think about getting
PG_lock:-(

> But given that this doesn't work right for some reason, can we use PG_error
> and then handle that appropriately in the filesystem's ->prepare_write() and
> ->page_mkwrite()?

Possibly, though I'd rather they didn't see such a page.

David
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