From: Trond Myklebust Subject: Re: [PATCH] nfs: clear_commit_release incorrectly handle truncated page Date: Tue, 02 Feb 2010 10:36:39 -0500 Message-ID: <1265124999.3177.27.camel@localhost> References: <87hbpzhqlp.fsf@openvz.org> <1265123045.3177.21.camel@localhost> <87eil3pszw.fsf@openvz.org> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Cc: Linux Kernel Mailing List , linux-nfs@vger.kernel.org To: Dmitry Monakhov Return-path: Received: from mail-out2.uio.no ([129.240.10.58]:37855 "EHLO mail-out2.uio.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756454Ab0BBPgn (ORCPT ); Tue, 2 Feb 2010 10:36:43 -0500 In-Reply-To: <87eil3pszw.fsf@openvz.org> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Tue, 2010-02-02 at 18:17 +0300, Dmitry Monakhov wrote: > Trond Myklebust writes: > > > On Tue, 2010-02-02 at 13:36 +0300, Dmitry Monakhov wrote: > >> After page was truncated it lost it's mapping, this result in null > >> pointer dereference on bdi_stat update. In fact we have to decrement > >> bdi_stat even for truncated pages, so let's pass correct mapping in > >> function arguments. Patch against linux-2.6 > >> ##TEST_CASE > >> /* > >> Tast case for bug in nfs_clear_request_commit() > >> caused by null pointer dereference in case of truncated page. > >> It takes less than 10 minutes to reproduce the bug. > > > > Something is wrong here. nfs_release_page() returns '0' if the > > page has an associated write request (i.e. PagePrivate is set), and so > > both invalidate_complete_page() and invalidate_complete_page2() will > > fail. > > > > So what is truncating the page? > truncate_inode_page() > truncate_complete_page() > if (page_has_private(page)) > do_invalidatepage() > ->nfs_invalidate_page() do_invalidate_page() is called before remove_from_page_cache(), so page->mapping should still be set. Trond