From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Moyer Subject: Re: [autofs] [RFC PATCH]autofs4: hang and proposed fix Date: Tue, 6 Dec 2005 17:37:53 -0500 Message-ID: <17302.4801.459854.80468@segfault.boston.redhat.com> References: <438F251B.7060602@us.ibm.com> <43906968.6080508@us.ibm.com> <1133547148.8976.25.camel@lade.trondhjem.org> <20051204125612.GA28229@infradead.org> <20051204125740.GB28229@infradead.org> <20051204171729.GA31111@infradead.org> <17302.157.540958.723305@segfault.boston.redhat.com> <20051206214033.GA31000@infradead.org> Reply-To: jmoyer@redhat.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: Ian Kent , Trond Myklebust , Will Taber , Ram Pai , autofs mailing list , linux-fsdevel Return-path: Received: from mx1.redhat.com ([66.187.233.31]:64403 "EHLO mx1.redhat.com") by vger.kernel.org with ESMTP id S932646AbVLFWi0 (ORCPT ); Tue, 6 Dec 2005 17:38:26 -0500 To: Christoph Hellwig In-Reply-To: <20051206214033.GA31000@infradead.org> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org ==> Regarding Re: [autofs] [RFC PATCH]autofs4: hang and proposed fix; Christoph Hellwig adds: hch> On Tue, Dec 06, 2005 at 04:20:29PM -0500, Jeff Moyer wrote: No, for hch> current TOT that can't happen. It could happen for older kernels but hch> nothing is doing it in the tree anymore and if anything outside is hch> doing it it's fundamentally broken. >> This is a bit unclear to me. What do you mean when you refer to "it" >> and "that" above? Oh, and TOT is a TLA I haven't run across before. hch> TOT = top of tree. hch> To rephrease the above: With current mainline the nameidata argument hch> is always valid when ->lookup or ->d_revalidate are called except when hch> the filesystem uses lookup_one_len. lookup_one_len is a helper for hch> fileystem usage that is only valid to be used on the filesystems own hch> trees. >> We know that there is at least one out of tree module that calls >> lookup_one_len, and ends up in the autofs4 revalidate code without the >> valid nameidata structure. In this case, with your patch, wouldn't we >> blindly dereference the structure and cause an oops? If so, who is at >> fault? hch> This out of tree module is wrong and always has been wrong. Any hch> actual breakage of such a module is expected. Thanks for the clarification. This was my interpretation, but I wanted to be sure. hch> Do you happen to know what module that is? Well, the example originally posted was stubfs, which was purported to be a sample fs used to show this problem. Perhaps the original reporter can tell us what other code does this. -Jeff