Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753181AbaAQSBy (ORCPT ); Fri, 17 Jan 2014 13:01:54 -0500 Received: from iolanthe.rowland.org ([192.131.102.54]:54913 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1752144AbaAQSBu (ORCPT ); Fri, 17 Jan 2014 13:01:50 -0500 Date: Fri, 17 Jan 2014 13:01:49 -0500 (EST) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Oleg Nesterov cc: Peter Zijlstra , Greg Kroah-Hartman , , Ingo Molnar , Thomas Gleixner , Steven Rostedt , Paul McKenney , Linus Torvalds Subject: Re: check && lockdep_no_validate (Was: lockdep: Introduce wait-type checks) In-Reply-To: <20140117163111.GA5764@redhat.com> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 17 Jan 2014, Oleg Nesterov wrote: > On 01/16, Alan Stern wrote: > > > > On Thu, 16 Jan 2014, Peter Zijlstra wrote: > > > > > On Thu, Jan 16, 2014 at 06:43:48PM +0100, Oleg Nesterov wrote: > > > > > > Perhaps we should change the meaning of lockdep_set_novalidate_class? > > > > (perhaps with rename). What do you think about the patch below? > > > > > > > > With this patch __lockdep_no_validate__ means "automatically nested", > > > > > > Yes, I suppose that might work, it would allow some validation. > > > > I haven't seen the patch, but I'm not so sure it will work. Suppose we > > have two devices, D1 and D2, and some other mutex, M. Then the locking > > pattern: > > > > lock(D1); > > lock(M); > > unlock(M); > > unlock(D1); > > > > generally should not conflict with: > > > > lock(M); > > lock(D2); > > unlock(D2); > > unlock(M); > > Yes, sure. This change assumes that the only problem in drivers/base is > dev->parent->mutex / dev->mutex dependency. If the locking is even more > "broken" (wrt lockdep), we can't replace lockdep_set_novalidate_class() > with lockdep_set_auto_nested(). I suspect it is even more "broken". But I can't point to specific examples. > And, otoh, with this change lockdep can miss the real problems too, for > example: > > func1(dev) > { > device_lock(dev->parent); > mutex_lock(MUTEX); > device_lock(dev); > ... > } > > func2(dev) > { > device_lock(dev); > mutex_lock(MUTEX); > ... > } > > lockdep will only notice dev -> MUTEX dependency. > > I booted the kernel (under kvm) with this change and there is nothing > in dmesg, but of course this is not the real testing. > > So do you think that dev->mutex should not be validated at all ? My guess is that if your change is deployed widely, there will be reports of violations. That's only a guess. Still, you could go ahead and try it, just to see what happens. > Just in case... Of course, if we actually add auto_nested we should not > use a single class unless dev->mutex will be the only user. That's a good point. I don't know of any other classes using LOCKDEP_NO_VALIDATE, but there may be one or two. Also, take a look at commit 356c05d58af0. It's a similar situation (not exactly the same). Alan Stern -- 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/