From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932968Ab1EJQWG (ORCPT ); Tue, 10 May 2011 12:22:06 -0400 Received: from e1.ny.us.ibm.com ([32.97.182.141]:58011 "EHLO e1.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932859Ab1EJQWE (ORCPT ); Tue, 10 May 2011 12:22:04 -0400 Date: Tue, 10 May 2011 09:21:58 -0700 From: "Paul E. McKenney" To: Ingo Molnar Cc: Valdis.Kletnieks@vt.edu, Andrew Morton , Peter Zijlstra , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: 2.6.39-rc6-mmotm0506 - lockdep splat in RCU code on page fault Message-ID: <20110510162158.GK2258@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <6921.1304989476@localhost> <20110510082029.GF2258@linux.vnet.ibm.com> <20110510085746.GG27426@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110510085746.GG27426@elte.hu> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 10, 2011 at 10:57:46AM +0200, Ingo Molnar wrote: > > * Paul E. McKenney wrote: > > > - raw_spin_lock_irqsave(&rnp->lock, flags); > > - rnp->wakemask |= rdp->grpmask; > > - raw_spin_unlock_irqrestore(&rnp->lock, flags); > > + do { > > + old = rnp->wakemask; > > + new = old | rdp->grpmask; > > + } while (cmpxchg(&rnp->wakemask, old, new) != old); > > Hm, isnt this an inferior version of atomic_or_long() in essence? > > Note that atomic_or_long() is x86 only, so a generic one would have to be > offered too i suspect, atomic_cmpxchg() driven or so - which would look like > the above loop. > > Most architectures could offer atomic_or_long() i suspect. Is the following what you had in mind? This (untested) patch provides only the generic function: if this is what you had in mind, I can put together optimized versions for a couple of the architectures. Thanx, Paul ------------------------------------------------------------------------ diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index cc6c53a..e7c2e69 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -171,6 +171,9 @@ config ARCH_HAS_DEFAULT_IDLE config ARCH_HAS_CACHE_LINE_SIZE def_bool y +config ARCH_HAS_ATOMIC_OR_LONG + def_bool X86_64 + config HAVE_SETUP_PER_CPU_AREA def_bool y diff --git a/include/linux/atomic.h b/include/linux/atomic.h index 96c038e..2fc3222 100644 --- a/include/linux/atomic.h +++ b/include/linux/atomic.h @@ -34,4 +34,17 @@ static inline int atomic_inc_not_zero_hint(atomic_t *v, int hint) } #endif +#ifndef CONFIG_ARCH_HAS_ATOMIC_OR_LONG +static inline void atomic_or_long(unsigned long *v1, unsigned long v2) +{ + unsigned long old; + unsigned long new; + + do { + old = ACCESS_ONCE(*v1); + new = old | v2; + } while (cmpxchg(v1, old, new) != old); +} +#endif /* #ifndef CONFIG_ARCH_HAS_ATOMIC_OR_LONG */ + #endif /* _LINUX_ATOMIC_H */ diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 20c22c5..86f44a3 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -36,7 +36,7 @@ #include #include #include -#include +#include #include #include #include @@ -1525,15 +1525,10 @@ static void rcu_cpu_kthread_setrt(int cpu, int to_rt) */ static void rcu_cpu_kthread_timer(unsigned long arg) { - unsigned long old; - unsigned long new; struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, arg); struct rcu_node *rnp = rdp->mynode; - do { - old = rnp->wakemask; - new = old | rdp->grpmask; - } while (cmpxchg(&rnp->wakemask, old, new) != old); + atomic_or_long(&rnp->wakemask, rdp->grpmask); invoke_rcu_node_kthread(rnp); }