Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754512AbbEZQ2z (ORCPT ); Tue, 26 May 2015 12:28:55 -0400 Received: from e31.co.us.ibm.com ([32.97.110.149]:41806 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754412AbbEZQ2w (ORCPT ); Tue, 26 May 2015 12:28:52 -0400 Date: Tue, 26 May 2015 09:28:46 -0700 From: "Paul E. McKenney" To: Steven Rostedt Cc: Denys Vlasenko , Josh Triplett , Mathieu Desnoyers , Lai Jiangshan , Tejun Heo , Oleg Nesterov , linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] rcu: Deinline rcu_read_lock_sched_held() if DEBUG_LOCK_ALLOC Message-ID: <20150526162846.GI5989@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1432655314-10097-1-git-send-email-dvlasenk@redhat.com> <20150526120446.21c33307@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150526120446.21c33307@gandalf.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15052616-8236-0000-0000-00000BD1476F Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 8402 Lines: 202 On Tue, May 26, 2015 at 12:04:46PM -0400, Steven Rostedt wrote: > On Tue, 26 May 2015 17:48:34 +0200 > Denys Vlasenko wrote: > > > DEBUG_LOCK_ALLOC=y is not a production setting, but it is > > not very unusual either. Many developers routinely > > use kernels built with it enabled. > > > > Apart from being selected by hand, it is also auto-selected by > > PROVE_LOCKING "Lock debugging: prove locking correctness" and > > LOCK_STAT "Lock usage statistics" config options. > > LOCK STAT is necessary for "perf lock" to work. > > > > I wouldn't spend too much time optimizing it, but this particular > > function has a very large cost in code size: when it is deinlined, > > code size decreases by 830,000 bytes: > > > > text data bss dec hex filename > > 85674192 22294776 20627456 128596424 7aa39c8 vmlinux.before > > 84837612 22294424 20627456 127759492 79d7484 vmlinux > > > > (with this config: http://busybox.net/~vda/kernel_config) > > > > Signed-off-by: Denys Vlasenko > > CC: "Paul E. McKenney" > > CC: Josh Triplett > > CC: Steven Rostedt > > CC: Mathieu Desnoyers > > CC: Lai Jiangshan > > CC: Tejun Heo > > CC: Oleg Nesterov > > CC: linux-kernel@vger.kernel.org > > Reviewed-by: Steven Rostedt Thank you both! I had to apply by hand -- next time, please base on the rcu/dev branch of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git. Please also check to make sure that I didn't mess something up by my hand-applying, please see below. Thanx, Paul ------------------------------------------------------------------------ commit 523d371ef86584a28def5d23288babffdbcf5f85 Author: Denys Vlasenko Date: Tue May 26 17:48:34 2015 +0200 rcu: Deinline rcu_read_lock_sched_held() if DEBUG_LOCK_ALLOC DEBUG_LOCK_ALLOC=y is not a production setting, but it is not very unusual either. Many developers routinely use kernels built with it enabled. Apart from being selected by hand, it is also auto-selected by PROVE_LOCKING "Lock debugging: prove locking correctness" and LOCK_STAT "Lock usage statistics" config options. LOCK STAT is necessary for "perf lock" to work. I wouldn't spend too much time optimizing it, but this particular function has a very large cost in code size: when it is deinlined, code size decreases by 830,000 bytes: text data bss dec hex filename 85674192 22294776 20627456 128596424 7aa39c8 vmlinux.before 84837612 22294424 20627456 127759492 79d7484 vmlinux (with this config: http://busybox.net/~vda/kernel_config) Signed-off-by: Denys Vlasenko CC: "Paul E. McKenney" CC: Josh Triplett CC: Mathieu Desnoyers CC: Lai Jiangshan CC: Tejun Heo CC: Oleg Nesterov CC: linux-kernel@vger.kernel.org Reviewed-by: Steven Rostedt Signed-off-by: Paul E. McKenney diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 18e377b92875..3a4d1bf430b1 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -467,46 +467,10 @@ int rcu_read_lock_bh_held(void); * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an * RCU-sched read-side critical section. In absence of * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side - * critical section unless it can prove otherwise. Note that disabling - * of preemption (including disabling irqs) counts as an RCU-sched - * read-side critical section. This is useful for debug checks in functions - * that required that they be called within an RCU-sched read-side - * critical section. - * - * Check debug_lockdep_rcu_enabled() to prevent false positives during boot - * and while lockdep is disabled. - * - * Note that if the CPU is in the idle loop from an RCU point of - * view (ie: that we are in the section between rcu_idle_enter() and - * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU - * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs - * that are in such a section, considering these as in extended quiescent - * state, so such a CPU is effectively never in an RCU read-side critical - * section regardless of what RCU primitives it invokes. This state of - * affairs is required --- we need to keep an RCU-free window in idle - * where the CPU may possibly enter into low power mode. This way we can - * notice an extended quiescent state to other CPUs that started a grace - * period. Otherwise we would delay any grace period as long as we run in - * the idle task. - * - * Similarly, we avoid claiming an SRCU read lock held if the current - * CPU is offline. + * critical section unless it can prove otherwise. */ #ifdef CONFIG_PREEMPT_COUNT -static inline int rcu_read_lock_sched_held(void) -{ - int lockdep_opinion = 0; - - if (!debug_lockdep_rcu_enabled()) - return 1; - if (!rcu_is_watching()) - return 0; - if (!rcu_lockdep_current_cpu_online()) - return 0; - if (debug_locks) - lockdep_opinion = lock_is_held(&rcu_sched_lock_map); - return lockdep_opinion || preempt_count() != 0 || irqs_disabled(); -} +int rcu_read_lock_sched_held(void); #else /* #ifdef CONFIG_PREEMPT_COUNT */ static inline int rcu_read_lock_sched_held(void) { diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c index afaecb7a799a..fec5f48b8860 100644 --- a/kernel/rcu/update.c +++ b/kernel/rcu/update.c @@ -62,6 +62,55 @@ MODULE_ALIAS("rcupdate"); module_param(rcu_expedited, int, 0); +#if defined(CONFIG_DEBUG_LOCK_ALLOC) && defined(CONFIG_PREEMPT_COUNT) +/** + * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section? + * + * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an + * RCU-sched read-side critical section. In absence of + * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side + * critical section unless it can prove otherwise. Note that disabling + * of preemption (including disabling irqs) counts as an RCU-sched + * read-side critical section. This is useful for debug checks in functions + * that required that they be called within an RCU-sched read-side + * critical section. + * + * Check debug_lockdep_rcu_enabled() to prevent false positives during boot + * and while lockdep is disabled. + * + * Note that if the CPU is in the idle loop from an RCU point of + * view (ie: that we are in the section between rcu_idle_enter() and + * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU + * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs + * that are in such a section, considering these as in extended quiescent + * state, so such a CPU is effectively never in an RCU read-side critical + * section regardless of what RCU primitives it invokes. This state of + * affairs is required --- we need to keep an RCU-free window in idle + * where the CPU may possibly enter into low power mode. This way we can + * notice an extended quiescent state to other CPUs that started a grace + * period. Otherwise we would delay any grace period as long as we run in + * the idle task. + * + * Similarly, we avoid claiming an SRCU read lock held if the current + * CPU is offline. + */ +int rcu_read_lock_sched_held(void) +{ + int lockdep_opinion = 0; + + if (!debug_lockdep_rcu_enabled()) + return 1; + if (!rcu_is_watching()) + return 0; + if (!rcu_lockdep_current_cpu_online()) + return 0; + if (debug_locks) + lockdep_opinion = lock_is_held(&rcu_sched_lock_map); + return lockdep_opinion || preempt_count() != 0 || irqs_disabled(); +} +EXPORT_SYMBOL(rcu_read_lock_sched_held); +#endif + #ifndef CONFIG_TINY_RCU static atomic_t rcu_expedited_nesting = -- 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/