From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752669Ab2GaRS1 (ORCPT ); Tue, 31 Jul 2012 13:18:27 -0400 Received: from e34.co.us.ibm.com ([32.97.110.152]:40804 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751166Ab2GaRSZ (ORCPT ); Tue, 31 Jul 2012 13:18:25 -0400 Date: Tue, 31 Jul 2012 10:17:33 -0700 From: "Paul E. McKenney" To: Steven Rostedt Cc: Fengguang Wu , Steven Rostedt , LKML , David Howells Subject: Re: __update_max_tr: rcu_read_lock() used illegally while idle! Message-ID: <20120731171733.GK2422@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20120724090330.GA9830@localhost> <1343662752.3847.2.camel@fedora> <20120731120556.GB17252@localhost> <1343741625.27983.39.camel@gandalf.stny.rr.com> <20120731144453.GB2422@linux.vnet.ibm.com> <1343746311.27983.52.camel@gandalf.stny.rr.com> <1343746583.27983.55.camel@gandalf.stny.rr.com> <20120731151808.GF2422@linux.vnet.ibm.com> <1343749502.27983.57.camel@gandalf.stny.rr.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1343749502.27983.57.camel@gandalf.stny.rr.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12073117-1780-0000-0000-000007EAF51E X-IBM-ISS-SpamDetectors: X-IBM-ISS-DetailInfo: BY=3.00000288; HX=3.00000193; KW=3.00000007; PH=3.00000001; SC=3.00000006; SDB=6.00161324; UDB=6.00036461; UTC=2012-07-31 17:18:23 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 31, 2012 at 11:45:02AM -0400, Steven Rostedt wrote: > On Tue, 2012-07-31 at 08:18 -0700, Paul E. McKenney wrote: > > On Tue, Jul 31, 2012 at 10:56:23AM -0400, Steven Rostedt wrote: > > > On Tue, 2012-07-31 at 10:51 -0400, Steven Rostedt wrote: > > > > > > > > OK, I will bite. How about using something like RCU_NONIDLE(), either > > > > > directly or open-coded, to make it a legal call site? > > > > > > > > OK, then something like: > > > > > > > > RCU_NONIDLE(max_data = task_uid(tsk)); > > > > > > > > would work when called normally or with idle? > > > > > > > > > > The comment above RCU_NONIDLE() says: > > > > > > This macro may be used from process-level code only. > > > > > > Although I'm not sure what a 'level' is. Do you mean process-context? If > > > so, then this will not work because it can be called from non process > > > level code (return from interrupt), or any interrupt that enables > > > interrupts. > > > > Yep, process context. It seems that I was naively expecting the > > calls in interrupt context to be covered by rcu_irq_enter() and > > rcu_irq_exit(). I take it that these calls are happening outside of > > the rcu_irq_enter()-protected region? > > Yep, it is called by the same hooks that lockdep uses. TRACE_IRQS_ON > inside the irq handler in assembly. Does the following patch help? Thanx, Paul ------------------------------------------------------------------------ rcu: Permit RCU_NONIDLE() to be used from interrupt context There is a need to use RCU from interrupt context, but either before rcu_irq_enter() is called or after rcu_irq_exit() is called. If the interrupt occurs from idle, then lockdep-RCU will complain about such uses, as they appear to be illegal uses of RCU from the idle loop. In other environments, RCU_NONIDLE() could be used to properly protect the use of RCU, but RCU_NONIDLE() currently cannot be invoked except from process context. This commit therefore modifies RCU_NONIDLE() to permit its use more globally. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 115ead2..4eab81a 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -210,14 +210,12 @@ extern void exit_rcu(void); * to nest RCU_NONIDLE() wrappers, but the nesting level is currently * quite limited. If deeper nesting is required, it will be necessary * to adjust DYNTICK_TASK_NESTING_VALUE accordingly. - * - * This macro may be used from process-level code only. */ #define RCU_NONIDLE(a) \ do { \ - rcu_idle_exit(); \ + rcu_irq_exit(); \ do { a; } while (0); \ - rcu_idle_enter(); \ + rcu_irq_enter(); \ } while (0) /* diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c index 31a10f9..aee6df8 100644 --- a/kernel/rcutiny.c +++ b/kernel/rcutiny.c @@ -115,6 +115,7 @@ void rcu_irq_exit(void) rcu_idle_enter_common(newval); local_irq_restore(flags); } +EXPORT_SYMBOL_GPL(rcu_irq_exit); /* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */ static void rcu_idle_exit_common(long long oldval) @@ -172,6 +173,7 @@ void rcu_irq_enter(void) rcu_idle_exit_common(oldval); local_irq_restore(flags); } +EXPORT_SYMBOL_GPL(rcu_irq_enter); #ifdef CONFIG_DEBUG_LOCK_ALLOC diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 44609c3..2175b13 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -455,6 +455,7 @@ void rcu_irq_exit(void) rcu_idle_enter_common(rdtp, oldval); local_irq_restore(flags); } +EXPORT_SYMBOL_GPL(rcu_irq_exit); /* * rcu_idle_exit_common - inform RCU that current CPU is moving away from idle @@ -550,6 +551,7 @@ void rcu_irq_enter(void) rcu_idle_exit_common(rdtp, oldval); local_irq_restore(flags); } +EXPORT_SYMBOL_GPL(rcu_irq_enter); /** * rcu_nmi_enter - inform RCU of entry to NMI context