Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751663Ab0FPEEP (ORCPT ); Wed, 16 Jun 2010 00:04:15 -0400 Received: from out1.smtp.messagingengine.com ([66.111.4.25]:41729 "EHLO out1.smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750759Ab0FPEEM (ORCPT ); Wed, 16 Jun 2010 00:04:12 -0400 X-Sasl-enc: WhDgvEPQOzHzA2Go0ZnKdnwtsGgIgvJMh3Ot6R/CHAsJ 1276661050 Subject: Re: [autofs] [PATCH 04/38] autofs4: Save autofs trigger's vfsmount in super block info From: Ian Kent To: Valerie Aurora Cc: Alexander Viro , autofs@linux.kernel.org, Miklos Szeredi , linux-kernel@vger.kernel.org, Christoph Hellwig , linux-fsdevel@vger.kernel.org, Jan Blunck In-Reply-To: <1276627208-17242-5-git-send-email-vaurora@redhat.com> References: <1276627208-17242-1-git-send-email-vaurora@redhat.com> <1276627208-17242-5-git-send-email-vaurora@redhat.com> Content-Type: text/plain; charset="UTF-8" Date: Wed, 16 Jun 2010 12:04:03 +0800 Message-ID: <1276661043.2339.35.camel@localhost> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 (2.28.3-1.fc12) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4714 Lines: 130 On Tue, 2010-06-15 at 11:39 -0700, Valerie Aurora wrote: > From: Jan Blunck > > XXX - This is broken and included just to make union mounts work. See > discussion at: > > http://kerneltrap.org/mailarchive/linux-fsdevel/2010/1/15/6708053/thread Instead of saving the vfsmount we could save a pointer to the dentry of the mount point in the autofs super block info struct. I think that's the bit I don't have so it would be sufficient for a lookup_mnt() for the needed vfsmount in ->follow_mount(). Objections? Suggestions? > > Original commit message: > > This is a bugfix/replacement for commit > 051d381259eb57d6074d02a6ba6e90e744f1a29f: > > During a path walk if an autofs trigger is mounted on a dentry, > when the follow_link method is called, the nameidata struct > contains the vfsmount and mountpoint dentry of the parent mount > while the dentry that is passed in is the root of the autofs > trigger mount. I believe it is impossible to get the vfsmount of > the trigger mount, within the follow_link method, when only the > parent vfsmount and the root dentry of the trigger mount are > known. > > The solution in this commit was to replace the path embedded in the > parent's nameidata with the path of the link itself in > __do_follow_link(). This is a relatively harmless misuse of the > field, but union mounts ran into a bug during follow_link() caused by > the nameidata containing the wrong path (we count on it being what it > is all other places - the path of the parent). > > A cleaner and easier to understand solution is to save the necessary > vfsmount in the autofs superblock info when it is mounted. Then we > can easily update the vfsmount in autofs4_follow_link(). > > Signed-off-by: Jan Blunck > Signed-off-by: Valerie Aurora > Acked-by: Ian Kent > Cc: autofs@linux.kernel.org > Cc: Alexander Viro > --- > fs/autofs4/autofs_i.h | 1 + > fs/autofs4/init.c | 11 ++++++++++- > fs/autofs4/root.c | 6 ++++++ > fs/namei.c | 7 ++----- > 4 files changed, 19 insertions(+), 6 deletions(-) > > diff --git a/fs/autofs4/autofs_i.h b/fs/autofs4/autofs_i.h > index 3d283ab..de3af64 100644 > --- a/fs/autofs4/autofs_i.h > +++ b/fs/autofs4/autofs_i.h > @@ -133,6 +133,7 @@ struct autofs_sb_info { > int reghost_enabled; > int needs_reghost; > struct super_block *sb; > + struct vfsmount *mnt; > struct mutex wq_mutex; > spinlock_t fs_lock; > struct autofs_wait_queue *queues; /* Wait queue pointer */ > diff --git a/fs/autofs4/init.c b/fs/autofs4/init.c > index 9722e4b..5e0dcd7 100644 > --- a/fs/autofs4/init.c > +++ b/fs/autofs4/init.c > @@ -17,7 +17,16 @@ > static int autofs_get_sb(struct file_system_type *fs_type, > int flags, const char *dev_name, void *data, struct vfsmount *mnt) > { > - return get_sb_nodev(fs_type, flags, data, autofs4_fill_super, mnt); > + struct autofs_sb_info *sbi; > + int ret; > + > + ret = get_sb_nodev(fs_type, flags, data, autofs4_fill_super, mnt); > + if (ret) > + return ret; > + > + sbi = autofs4_sbi(mnt->mnt_sb); > + sbi->mnt = mnt; > + return 0; > } > > static struct file_system_type autofs_fs_type = { > diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c > index e8e5e63..c41e01d 100644 > --- a/fs/autofs4/root.c > +++ b/fs/autofs4/root.c > @@ -219,6 +219,12 @@ static void *autofs4_follow_link(struct dentry *dentry, struct nameidata *nd) > DPRINTK("dentry=%p %.*s oz_mode=%d nd->flags=%d", > dentry, dentry->d_name.len, dentry->d_name.name, oz_mode, > nd->flags); > + > + dput(nd->path.dentry); > + mntput(nd->path.mnt); > + nd->path.mnt = mntget(sbi->mnt); > + nd->path.dentry = dget(dentry); > + > /* > * For an expire of a covered direct or offset mount we need > * to break out of follow_down() at the autofs mount trigger > diff --git a/fs/namei.c b/fs/namei.c > index 3b43c48..f731108 100644 > --- a/fs/namei.c > +++ b/fs/namei.c > @@ -538,11 +538,8 @@ __do_follow_link(struct path *path, struct nameidata *nd, void **p) > touch_atime(path->mnt, dentry); > nd_set_link(nd, NULL); > > - if (path->mnt != nd->path.mnt) { > - path_to_nameidata(path, nd); > - dget(dentry); > - } > - mntget(path->mnt); > + if (path->mnt == nd->path.mnt) > + mntget(nd->path.mnt); > nd->last_type = LAST_BIND; > *p = dentry->d_inode->i_op->follow_link(dentry, nd); > error = PTR_ERR(*p); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/