Return-Path: Received: from mail-pd0-f176.google.com ([209.85.192.176]:35465 "EHLO mail-pd0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755030AbbEEDxe (ORCPT ); Mon, 4 May 2015 23:53:34 -0400 Received: by pdbqd1 with SMTP id qd1so181874064pdb.2 for ; Mon, 04 May 2015 20:53:33 -0700 (PDT) Message-ID: <55483EB7.5060104@gmail.com> Date: Tue, 05 May 2015 11:53:27 +0800 From: Kinglong Mee MIME-Version: 1.0 To: "J. Bruce Fields" , NeilBrown CC: "linux-nfs@vger.kernel.org" , Al Viro , kinglongmee@gmail.com, Steve Dickson Subject: Re: [PATCH RFC] NFSD: fix cannot umounting mount points under pseudo root References: <20150421215417.GE13782@fieldses.org> <553781E2.1000900@gmail.com> <20150422150703.GA1247@fieldses.org> <20150423094431.1a8aa68b@notabene.brown> <5538EB18.7080802@gmail.com> <20150424130045.6bbdb2f9@notabene.brown> <553E2784.6020906@gmail.com> <20150429125728.69ddfc6c@notabene.brown> <20150429191934.GA23980@fieldses.org> <20150430075225.21a71056@notabene.brown> <20150430213602.GB9509@fieldses.org> In-Reply-To: <20150430213602.GB9509@fieldses.org> Content-Type: text/plain; charset=windows-1252 Sender: linux-nfs-owner@vger.kernel.org List-ID: Cc Steve, Viro, On 5/1/2015 5:36 AM, J. Bruce Fields wrote: > On Thu, Apr 30, 2015 at 07:52:25AM +1000, NeilBrown wrote: >> On Wed, 29 Apr 2015 15:19:34 -0400 "J. Bruce Fields" >> wrote: >>> Maybe drop the locking from nfsd_buffered_readdir and *just* take the >>> i_mutex around lookup_one_len(), if that's the only place we need it? As description in other thread, before the upcall to rpc.mountd, nfsd have call lookup_one_len() for the file, but why rpc.mountd also blocked in lookup ? There is a bug in rpc.mountd when checking sub-directory, it sets bad patch length for child. If parent if "/nfs/xfs" and child is "/nfs/test", the child name will be truncated to "/nfs/tes" for strlen(parent), "/nfs/test" have exist in kernel's cache for the lookup_one_len(), but "/nfs/tes" is a bad path, which needs lookup_slow(), so blocked. static int is_subdirectory(char *child, char *parent) { /* Check is child is strictly a subdirectory of * parent or a more distant descendant. */ size_t l = strlen(parent); if (strcmp(parent, "/") == 0 && child[1] != 0) return 1; return (same_path(child, parent, l) && child[l] == '/'); } The following path makes a correct path, not a truncated path. Have be tested, everything is OK. thanks, Kinglong Mee -----------------------------------------------------------------------------------