From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753240AbbJNLH0 (ORCPT ); Wed, 14 Oct 2015 07:07:26 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:37968 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751904AbbJNLHZ (ORCPT ); Wed, 14 Oct 2015 07:07:25 -0400 Date: Wed, 14 Oct 2015 13:07:17 +0200 From: Peter Zijlstra To: Mark Brown Cc: Arnd Bergmann , Ingo Molnar , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Liam Girdwood , akpm@linux-foundation.org, Sascha Hauer Subject: Re: [PATCH] mutex: make mutex_lock_nested an inline function Message-ID: <20151014110717.GT17308@twins.programming.kicks-ass.net> References: <11282238.AHmyWliPRj@wuerfel> <20151013203812.GM17308@twins.programming.kicks-ass.net> <11817958.z9KtmeKzV7@wuerfel> <20151014082050.GQ17308@twins.programming.kicks-ass.net> <20151014102706.GR14956@sirena.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151014102706.GR14956@sirena.org.uk> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 14, 2015 at 11:27:06AM +0100, Mark Brown wrote: > On Wed, Oct 14, 2015 at 10:20:50AM +0200, Peter Zijlstra wrote: > > > Uuh, I just looked at next and saw this regulator_lock_supply() > > function. How is that limited? subclass must be <8 otherwise bad things > > happen. > > Can we please get some more discoverable documentation of the arbitrary > limits in the lockdep code? include/linux/lockdep.h:#define MAX_LOCKDEP_SUBCLASSES 8UL Also, it will give a runtime warn if you ever do hit that. > I seem to keep seeing code that bumps into > surprising limits like this and I'm not sure how I'm supposed to know > about them except through finding out after the fact or trawling the > code every time someone touches locking. Not knowing what other limits you've hit, I'm not entirely sure how to help out there. > I would be very surprised to see a system that pushes over 8 locks, > while there's nothing actually preventing it system design > considerations mean that even four cascaded supplies are pretty > unlikely so we should be fine. Every time you add a new level of > regulation you're both increasing the load on regulators up the chain > (which means they need to be bigger and more expensive) and except in > the case of a DCDC supplying an LDO (which only works to one level) > you're going to be decreasing the efficiency of the system. If we get > to that point we can worry about what to do. OK I suppose.