From mboxrd@z Thu Jan 1 00:00:00 1970 From: "J. Bruce Fields" Subject: Re: [RFC PATCH 05/13] vfs: take i_mutex on renamed file Date: Fri, 7 Sep 2012 17:39:01 -0400 Message-ID: <20120907213901.GA5927@fieldses.org> References: <1346878524-10585-1-git-send-email-bfields@redhat.com> <1346878524-10585-6-git-send-email-bfields@redhat.com> <20120906030526.GB6679@yanx> <20120906175118.GC21736@fieldses.org> <20120907022705.GA20453@yanx> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "J. Bruce Fields" , Al Viro , linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Guo Chao Return-path: Content-Disposition: inline In-Reply-To: <20120907022705.GA20453@yanx> Sender: linux-nfs-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-fsdevel.vger.kernel.org On Fri, Sep 07, 2012 at 10:27:05AM +0800, Guo Chao wrote: > On Thu, Sep 06, 2012 at 01:51:18PM -0400, J. Bruce Fields wrote: > > On Thu, Sep 06, 2012 at 11:05:26AM +0800, Guo Chao wrote: > > > On Wed, Sep 05, 2012 at 04:55:15PM -0400, J. Bruce Fields wrote: > > > > From: "J. Bruce Fields" > > > > diff --git a/fs/namei.c b/fs/namei.c > > > > index 1b46439..6156135 100644 > > > > --- a/fs/namei.c > > > > +++ b/fs/namei.c > > > > @@ -3658,6 +3658,7 @@ static int vfs_rename_other(struct inode *old_dir, struct dentry *old_dentry, > > > > struct inode *new_dir, struct dentry *new_dentry) > > > > { > > > > struct inode *target = new_dentry->d_inode; > > > > + struct inode *source = old_dentry->d_inode; > > > > int error; > > > > > > > > error = security_inode_rename(old_dir, old_dentry, new_dir, new_dentry); > > > > @@ -3665,8 +3666,7 @@ static int vfs_rename_other(struct inode *old_dir, struct dentry *old_dentry, > > > > return error; > > > > > > > > dget(new_dentry); > > > > - if (target) > > > > - mutex_lock(&target->i_mutex); > > > > + lock_two_nondirectories(source, target); > > > > > > > > error = -EBUSY; > > > > if (d_mountpoint(old_dentry)||d_mountpoint(new_dentry)) > > > > @@ -3681,8 +3681,7 @@ static int vfs_rename_other(struct inode *old_dir, struct dentry *old_dentry, > > > > if (!(old_dir->i_sb->s_type->fs_flags & FS_RENAME_DOES_D_MOVE)) > > > > d_move(old_dentry, new_dentry); > > > > out: > > > > - if (target) > > > > - mutex_unlock(&target->i_mutex); > > > > + unlock_two_nondirectories(source, target); > > > > dput(new_dentry); > > > > return error; > > > > } > > > > > > > > > > This change also fixes a race between rename and mount. > > > > > > Apparently we avoid to rename source or target if they are > > > mountpoint. But nothing prevents source being the mountpoint > > > after d_mountpoint check because we do not hold its i_mutex. > > > > > > Thus we are actually able to rename a mountpoint. > > > > > > Rename directory should also need this care. > > > > Do you have any practical way to reproduce that race? > > > > --b. > > Rename a mountpoint? Of course. > > One script ... > > #!/bin/bash > while true > do > mount -t sysfs nodev mnt && umount mnt > done > > > > The other ... > > #!/bin/bash > while true > do > mv mnt mnt2 && mv mnt2 mnt > done > > > > Run them simultaneously in two consoles. When mount keeps reporting > 'mount point mnt does not exist', stop them, then you will see the > familiar sysfs under mnt2. Oh, thanks, for some reason I assumed it would be more difficult to reproduce. I think we can do this--I don't think it even requires any care to the locking order of the renamed vs the victim directory, though I can't completely convince myself of that. Is it necessary to fix this, though? Does it cause any problems other than unexpected behavior? --b. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html