linux-kernel - NFS infinite loop in filemap

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Date:	Wed, 07 May 2008 22:34:38 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	trond.myklebust@....uio.no, npiggin@...e.de
CC:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: NFS infinite loop in filemap_fault()

Page fault on NFS apparently goes into an infinite loop if the read on
the server fails.

I don't understand the NFS readpage code, but the filemap_fault() code
looks somewhat suspicious:

	/*
	 * Umm, take care of errors if the page isn't up-to-date.
	 * Try to re-read it _once_. We do this synchronously,
	 * because there really aren't any performance issues here
	 * and we need to check for errors.
	 */
	ClearPageError(page);
	error = mapping->a_ops->readpage(file, page);
	page_cache_release(page);

	if (!error || error == AOP_TRUNCATED_PAGE)
		goto retry_find;

The comment doesn't seem to match what the it actually does: if
->readpage() is asynchronous, then this will just repeat everything,
without any guarantee that it will re-read once.

What am I missing?

Miklos
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