From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 663D9C10DCE for ; Fri, 6 Mar 2020 20:37:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4535720709 for ; Fri, 6 Mar 2020 20:37:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726674AbgCFUhQ (ORCPT ); Fri, 6 Mar 2020 15:37:16 -0500 Received: from zeniv.linux.org.uk ([195.92.253.2]:38968 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725873AbgCFUhQ (ORCPT ); Fri, 6 Mar 2020 15:37:16 -0500 Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1jAJiT-006Tvg-Sf; Fri, 06 Mar 2020 20:37:06 +0000 Date: Fri, 6 Mar 2020 20:37:05 +0000 From: Al Viro To: Miklos Szeredi Cc: Ian Kent , David Howells , Christian Brauner , James Bottomley , Steven Whitehouse , Miklos Szeredi , Christian Brauner , Jann Horn , "Darrick J. Wong" , Linux API , linux-fsdevel , lkml , Greg Kroah-Hartman Subject: Re: [PATCH 00/17] VFS: Filesystem information and notifications [ver #17] Message-ID: <20200306203705.GB23230@ZenIV.linux.org.uk> References: <1582644535.3361.8.camel@HansenPartnership.com> <20200228155244.k4h4hz3dqhl7q7ks@wittgenstein> <107666.1582907766@warthog.procyon.org.uk> <0403cda7345e34c800eec8e2870a1917a8c07e5c.camel@themaw.net> <20200306162549.GA28467@miu.piliscsaba.redhat.com> <20200306194322.GY23230@ZenIV.linux.org.uk> <20200306195823.GZ23230@ZenIV.linux.org.uk> <20200306200522.GA23230@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200306200522.GA23230@ZenIV.linux.org.uk> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Fri, Mar 06, 2020 at 08:05:22PM +0000, Al Viro wrote: > On Fri, Mar 06, 2020 at 07:58:23PM +0000, Al Viro wrote: > > On Fri, Mar 06, 2020 at 07:43:22PM +0000, Al Viro wrote: > > > On Fri, Mar 06, 2020 at 05:25:49PM +0100, Miklos Szeredi wrote: > > > > On Tue, Mar 03, 2020 at 08:46:09AM +0100, Miklos Szeredi wrote: > > > > > > > > > > I'm doing a patch. Let's see how it fares in the face of all these > > > > > preconceptions. > > > > > > > > Here's a first cut. Doesn't yet have superblock info, just mount info. > > > > Probably has rough edges, but appears to work. > > > > > > For starters, you have just made namespace_sem held over copy_to_user(). > > > This is not going to fly. > > > > In case if the above is too terse: you grab your mutex while under > > namespace_sem (see attach_recursive_mnt()); the same mutex is held > > while calling dir_emit(). Which can (and normally does) copy data > > to userland-supplied buffer. > > > > NAK for that reason alone, and to be honest I had been too busy > > suppressing the gag reflex to read and comment any deeper. > > > > I really hate that approach, in case it's not clear from the above. > > To the degree that I don't trust myself to filter out the obscenities > > if I try to comment on it right now. > > > > The only blocking thing we can afford under namespace_sem is GFP_KERNEL > > allocation. > > Incidentally, attach_recursive_mnt() only gets you the root(s) of > attached tree(s); try mount --rbind and see how much you've missed. You are misreading mntput_no_expire(), BTW - your get_mount() can bloody well race with umount(2), hitting the moment when we are done figuring out whether it's busy but hadn't cleaned ->mnt_ns (let alone set MNT_DOOMED) yet. If somebody calls umount(2) on a filesystem that is not mounted anywhere else, they are not supposed to see the sucker return 0 until the filesystem is shut down. You break that.