From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with SMTP id B38616B00BB for ; Thu, 4 Nov 2010 10:12:20 -0400 (EDT) Message-ID: <4CD2BF1C.10608@redhat.com> Date: Thu, 04 Nov 2010 10:11:40 -0400 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [PATCH] Revalidate page->mapping in do_generic_file_read() References: <20101103220941.C88FA932@kernel.beaverton.ibm.com> In-Reply-To: <20101103220941.C88FA932@kernel.beaverton.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Dave Hansen Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, arunabal@in.ibm.com, sbest@us.ibm.com, stable , Andrew Morton , Christoph Hellwig , Al Viro , Minchan Kim List-ID: On 11/03/2010 06:09 PM, Dave Hansen wrote: > 70 hours into some stress tests of a 2.6.32-based enterprise kernel, > we ran into a NULL dereference in here: > > int block_is_partially_uptodate(struct page *page, read_descriptor_t *desc, > unsigned long from) > { > ----> struct inode *inode = page->mapping->host; > > It looks like page->mapping was the culprit. (xmon trace is below). > After closer examination, I realized that do_generic_file_read() does > a find_get_page(), and eventually locks the page before calling > block_is_partially_uptodate(). However, it doesn't revalidate the > page->mapping after the page is locked. So, there's a small window > between the find_get_page() and ->is_partially_uptodate() where the > page could get truncated and page->mapping cleared. > > We _have_ a reference, so it can't get reclaimed, but it certainly > can be truncated. Acked-by: Rik van Riel -- All rights reversed -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org