From patchwork Wed Aug 23 01:06:54 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: NeilBrown X-Patchwork-Id: 9916439 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id F1B4C603F9 for ; Wed, 23 Aug 2017 01:08:15 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id BEEB12893D for ; Wed, 23 Aug 2017 01:08:15 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id B1E512894C; Wed, 23 Aug 2017 01:08:15 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, T_TVD_MIME_EPI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id A1FEC2893D for ; Wed, 23 Aug 2017 01:08:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752879AbdHWBHT (ORCPT ); Tue, 22 Aug 2017 21:07:19 -0400 Received: from mx2.suse.de ([195.135.220.15]:58353 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752841AbdHWBHS (ORCPT ); Tue, 22 Aug 2017 21:07:18 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (charybdis-ext.suse.de [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 5988BAB9B; Wed, 23 Aug 2017 01:07:16 +0000 (UTC) From: NeilBrown To: Ian Kent , Jeff Layton , Trond Myklebust , "viro\@zeniv.linux.org.uk" Date: Wed, 23 Aug 2017 11:06:54 +1000 Cc: "linux-kernel\@vger.kernel.org" , "mkoutny\@suse.com" , "linux-nfs\@vger.kernel.org" , "linux-fsdevel\@vger.kernel.org" , David Howells Subject: Re: Do we really need d_weak_revalidate??? In-Reply-To: <733c15c2-ffbb-9a89-90ec-3ba1d574590e@redhat.com> References: <87bmnmrai9.fsf@notabene.neil.brown.name> <1502430944.3822.1.camel@primarydata.com> <1502449309.4950.2.camel@redhat.com> <87zib3niqn.fsf@notabene.neil.brown.name> <1502705432.4978.1.camel@redhat.com> <877ey4nsep.fsf@notabene.neil.brown.name> <1502883253.4847.6.camel@redhat.com> <1e4665a6-30d6-c16a-760a-2892fb147760@redhat.com> <878tihmora.fsf@notabene.neil.brown.name> <2e289bba-677b-cc50-5fa3-2d24d1f6b858@redhat.com> <87h8x1l9qp.fsf@notabene.neil.brown.name> <733c15c2-ffbb-9a89-90ec-3ba1d574590e@redhat.com> Message-ID: <87r2w3jdn5.fsf@notabene.neil.brown.name> MIME-Version: 1.0 Sender: linux-nfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP On Mon, Aug 21 2017, Ian Kent wrote: >> >> A mount isn't triggered by kern_path(pathname, 0, &path). >> That '0' would need to include one of >> LOOKUP_PARENT | LOOKUP_DIRECTORY | >> LOOKUP_OPEN | LOOKUP_CREATE | LOOKUP_AUTOMOUNT >> >> to trigger an automount (otherwise you just get -EISDIR). > > It's perfectly sensible to think that but there is a case where a > a mount is triggered when using kern_path(). > > The EISDIR return occurs for positive dentrys, negative dentrys > will still trigger an automount (which is autofs specific, > indirect mount map using nobrowse option, the install default). Ok, I understand this better now. This difference between direct and indirect mounts is slightly awkward. It is visible from user-space, but not elegant to document. When you use O_PATH to open a direct automount that has not already been triggered, the open returns the underlying directory (and fstatfs confirms that it is AUTOFS_SUPER_MAGIC). When you use O_PATH on an indirect automount, it *will* trigger the automount when "nobrowse" is in effect, but it won't when "browse" is in effect. So we cannot just say "O_PATH doesn't trigger automounts", which is essentially what I said in https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=97a45d02e6671482e8b2cdcce3951930bf6bdb94 It might be possible to modify automount so that it was more consistent - i.e. if the point is triggered by a mkdir has been done, just to the mkdir. If it is triggered after a mkdir has been done, do the mount. I guess that might be racy, and in any case is hard to justify. Maybe I should change it to be about "direct automounts", and add a note that indirect automounts aren't so predictable. But back to my original issue of wanting to discard kern_path_mountpoint, what would you think of the following approach - slight revised from before. Thanks, NeilBrown diff --git a/fs/autofs4/autofs_i.h b/fs/autofs4/autofs_i.h index beef981aa54f..7663ea82e68d 100644 --- a/fs/autofs4/autofs_i.h +++ b/fs/autofs4/autofs_i.h @@ -135,10 +135,13 @@ static inline struct autofs_info *autofs4_dentry_ino(struct dentry *dentry) /* autofs4_oz_mode(): do we see the man behind the curtain? (The * processes which do manipulations for us in user space sees the raw * filesystem without "magic".) + * A process performing certain ioctls can get temporary oz status. */ +extern struct task_struct *autofs_tmp_oz; static inline int autofs4_oz_mode(struct autofs_sb_info *sbi) { - return sbi->catatonic || task_pgrp(current) == sbi->oz_pgrp; + return sbi->catatonic || task_pgrp(current) == sbi->oz_pgrp || + autofs_tmp_oz == current; } struct inode *autofs4_get_inode(struct super_block *, umode_t); diff --git a/fs/autofs4/dev-ioctl.c b/fs/autofs4/dev-ioctl.c index dd9f1bebb5a3..d76401669a20 100644 --- a/fs/autofs4/dev-ioctl.c +++ b/fs/autofs4/dev-ioctl.c @@ -200,6 +200,20 @@ static int autofs_dev_ioctl_protosubver(struct file *fp, return 0; } +struct task_struct *autofs_tmp_oz; +int kern_path_oz(const char *pathname, int flags, struct path *path) +{ + static DEFINE_MUTEX(autofs_oz); + int err; + + mutex_lock(&autofs_oz); + autofs_tmp_oz = current; + err = kern_path(pathname, flags, path); + autofs_tmp_oz = NULL; + mutex_unlock(&autofs_oz); + return err; +} + /* Find the topmost mount satisfying test() */ static int find_autofs_mount(const char *pathname, struct path *res, @@ -209,7 +223,8 @@ static int find_autofs_mount(const char *pathname, struct path path; int err; - err = kern_path_mountpoint(AT_FDCWD, pathname, &path, 0); + err = kern_path_oz(pathname, 0, &path); + if (err) return err; err = -ENOENT; @@ -552,8 +567,7 @@ static int autofs_dev_ioctl_ismountpoint(struct file *fp, if (!fp || param->ioctlfd == -1) { if (autofs_type_any(type)) - err = kern_path_mountpoint(AT_FDCWD, - name, &path, LOOKUP_FOLLOW); + err = kern_path_oz(name, LOOKUP_FOLLOW, &path); else err = find_autofs_mount(name, &path, test_by_type, &type);