From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757202AbcAOJpt (ORCPT ); Fri, 15 Jan 2016 04:45:49 -0500 Received: from casper.infradead.org ([85.118.1.10]:56370 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754760AbcAOJpr (ORCPT ); Fri, 15 Jan 2016 04:45:47 -0500 Date: Fri, 15 Jan 2016 10:45:41 +0100 From: Peter Zijlstra To: Stefan Agner Cc: broonie@kernel.org, festevam@gmail.com, mingo@redhat.com, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org Subject: Re: Lockdep warning when using REGCACHE_RBTREE Message-ID: <20160115094541.GH3421@worktop> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 14, 2016 at 02:30:50PM -0800, Stefan Agner wrote: > Hi Mark, > > I currently work on the DCU DRM driver (drivers/gpu/drm/fsl-dcu/) on a > Linux 4.4 kernel. With CONFIG_LOCKDEP enabled I get the following > warning on startup: > > [ 1.327284] ------------[ cut here ]------------ > [ 1.332010] WARNING: CPU: 0 PID: 1 at kernel/locking/lockdep.c:2755 lockdep_trace_alloc+0x120/0x124() > [ 1.341358] DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags)) > [ 1.521744] [<80375308>] (_regmap_write) from [<80376760>] (regmap_write+0x48/0x68) > [ 1.535348] [<80376718>] (regmap_write) from [<803538e8>] (fsl_dcu_drm_crtc_create+0x98/0xe8) > [ 1.549824] [<80353850>] (fsl_dcu_drm_crtc_create) from [<80352df0>] (fsl_dcu_drm_modeset_init+0x5c/0xfc) > The comment in __lockdep_trace_alloc says: > "Oi! Can't be having __GFP_FS allocations with IRQs disabled.". So _regmap_write() does: map->lock(map->lock_arg) Which isn't very enlightening, since that can be a mutex or a spinlock, the above strongly suggests spinlock though. Looking at __regmap_init(), this seems to depend on: (bus && bus->fast_io) || config->fast_io now, afaict, regmap_mmio is used in this case, which has .fast_io = true. So yeah, fail.