From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yb0-f200.google.com (mail-yb0-f200.google.com [209.85.213.200]) by kanga.kvack.org (Postfix) with ESMTP id 9348F6B0038 for ; Sat, 30 Dec 2017 18:01:03 -0500 (EST) Received: by mail-yb0-f200.google.com with SMTP id l65so13210220ybc.9 for ; Sat, 30 Dec 2017 15:01:03 -0800 (PST) Received: from imap.thunk.org (imap.thunk.org. [2600:3c02::f03c:91ff:fe96:be03]) by mx.google.com with ESMTPS id x126si1486897ybb.320.2017.12.30.15.01.02 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sat, 30 Dec 2017 15:01:02 -0800 (PST) Date: Sat, 30 Dec 2017 18:00:57 -0500 From: Theodore Ts'o Subject: Re: About the try to remove cross-release feature entirely by Ingo Message-ID: <20171230230057.GB12995@thunk.org> References: <20171229014736.GA10341@X58A-UD3R> <20171229035146.GA11757@thunk.org> <20171229072851.GA12235@X58A-UD3R> <20171230061624.GA27959@bombadil.infradead.org> <20171230154041.GB3366@thunk.org> <20171230204417.GF27959@bombadil.infradead.org> <20171230224028.GC3366@thunk.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171230224028.GC3366@thunk.org> Sender: owner-linux-mm@kvack.org List-ID: To: Matthew Wilcox , Byungchul Park , Byungchul Park , Thomas Gleixner , Peter Zijlstra , Ingo Molnar , david@fromorbit.com, Linus Torvalds , Amir Goldstein , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, oleg@redhat.com, kernel-team@lge.com, daniel@ffwll.ch On Sat, Dec 30, 2017 at 05:40:28PM -0500, Theodore Ts'o wrote: > On Sat, Dec 30, 2017 at 12:44:17PM -0800, Matthew Wilcox wrote: > > > > I'm not sure I agree with this part. What if we add a new TCP lock class > > for connections which are used for filesystems/network block devices/...? > > Yes, it'll be up to each user to set the lockdep classification correctly, > > but that's a relatively small number of places to add annotations, > > and I don't see why it wouldn't work. > > I was exagerrating a bit for effect, I admit. (but only a bit). > > It can probably be for all TCP connections that are used by kernel > code (as opposed to userspace-only TCP connections). But it would > probably have to be each and every device-mapper instance, each and > every block device, each and every mounted file system, each and every > bdi object, etc. Clarification: all TCP connections that are used by kernel code would need to be in their own separate lock class. All TCP connections used only by userspace could be in their own shared lock class. You can't use a one lock class for all kernel-used TCP connections, because of the Network Block Device mounted on a local file system which is then exported via NFS and squirted out yet another TCP connection problem. Also, what to do with TCP connections which are created in userspace (with some authentication exchanges happening in userspace), and then passed into kernel space for use in kernel space, is an interesting question. So "all you have to do is classify the locks 'properly'" is much like the apocrophal, "all you have to do is bell the cat"[1]. Or like the saying, "colonizing the stars is *easy*; all you have to do is figure out faster than light travel." [1] https://en.wikipedia.org/wiki/Belling_the_cat - Ted -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org