Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755474AbbBFONy (ORCPT ); Fri, 6 Feb 2015 09:13:54 -0500 Received: from casper.infradead.org ([85.118.1.10]:34098 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754479AbbBFONw (ORCPT ); Fri, 6 Feb 2015 09:13:52 -0500 Date: Fri, 6 Feb 2015 15:13:46 +0100 From: Peter Zijlstra To: Peter Ujfalusi Cc: Tony Lindgren , paul@pwsan.com, linux-omap@vger.kernel.org, mingo@redhat.com, linux-kernel@vger.kernel.org, balbi@ti.com, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH 0/2] ARM: omap2+: omap_hwmod: Fix false lockdep warning Message-ID: <20150206141346.GP21418@twins.programming.kicks-ass.net> References: <1423226916-18804-1-git-send-email-peter.ujfalusi@ti.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1423226916-18804-1-git-send-email-peter.ujfalusi@ti.com> 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 Content-Length: 3407 Lines: 81 On Fri, Feb 06, 2015 at 02:48:34PM +0200, Peter Ujfalusi wrote: > Hi, > > In case when hwmods are used in nested way the lockdep validator will print out > a warning message about possible deadlock situation: > > [ 4.514882] ============================================= > [ 4.520530] [ INFO: possible recursive locking detected ] > [ 4.526176] 3.14.30-00289-ge44872fdca8f-dirty #198 Not tainted > [ 4.532285] --------------------------------------------- > [ 4.537936] kworker/u4:1/18 is trying to acquire lock: > [ 4.543317] (&(&oh->_lock)->rlock){......}, at: [] omap_hwmod_enable+0x2c/0x58 > [ 4.552109] > [ 4.552109] but task is already holding lock: > [ 4.558216] (&(&oh->_lock)->rlock){......}, at: [] omap_hwmod_enable+0x2c/0x58 > [ 4.566999] > [ 4.566999] other info that might help us debug this: > [ 4.573831] Possible unsafe locking scenario: > [ 4.573831] > [ 4.580025] CPU0 > [ 4.582584] ---- > [ 4.585142] lock(&(&oh->_lock)->rlock); > [ 4.589544] lock(&(&oh->_lock)->rlock); > [ 4.593945] > [ 4.593945] *** DEADLOCK *** > [ 4.593945] > [ 4.600146] May be due to missing lock nesting notation > > What lockdep did not realizes is that the two oh is not the same hwmod object > and we have taken different locks. > > One example of nested hwmod usage is on DRA7xx platforms, where McASP can be > configured to use ATL clock as it's functional clock. In this case the > pm_runtime_get/put_sync call will enable the mcasp hwmod and as part of this > operation it will enable the needed clocks. Since ATL clock is needed, we will > have another pm_runtime operation from the ATL clock enable callback which > will take the atl hwmod's lock. This will be seen by lockdep as possible > deadlock situation. > > In order to notify lockdep about this, we need to switch using _nested > version of locking function and assign different subclass to those hwmods which > could be used in nested way. IFF struct omap_hwmod is always statically allocated; as I think the __init on _register() mandates, you can use the below annotation. --- arch/arm/mach-omap2/omap_hwmod.c | 1 + arch/arm/mach-omap2/omap_hwmod.h | 2 ++ 2 files changed, 3 insertions(+) diff --git a/arch/arm/mach-omap2/omap_hwmod.c b/arch/arm/mach-omap2/omap_hwmod.c index 9025ffffd2dc..222d654ad6fd 100644 --- a/arch/arm/mach-omap2/omap_hwmod.c +++ b/arch/arm/mach-omap2/omap_hwmod.c @@ -2698,6 +2698,7 @@ static int __init _register(struct omap_hwmod *oh) INIT_LIST_HEAD(&oh->master_ports); INIT_LIST_HEAD(&oh->slave_ports); spin_lock_init(&oh->_lock); + lockdep_set_class(&oh->_lock, &oh->hwmod_key); oh->_state = _HWMOD_STATE_REGISTERED; diff --git a/arch/arm/mach-omap2/omap_hwmod.h b/arch/arm/mach-omap2/omap_hwmod.h index 5b42fafcaf55..754bdfb3f811 100644 --- a/arch/arm/mach-omap2/omap_hwmod.h +++ b/arch/arm/mach-omap2/omap_hwmod.h @@ -689,6 +689,8 @@ struct omap_hwmod { u8 _state; u8 _postsetup_state; struct omap_hwmod *parent_hwmod; + + struct lock_class_key hwmod_key; }; struct omap_hwmod *omap_hwmod_lookup(const char *name); -- 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/