Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759272AbZIPP5U (ORCPT ); Wed, 16 Sep 2009 11:57:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758306AbZIPP5S (ORCPT ); Wed, 16 Sep 2009 11:57:18 -0400 Received: from e4.ny.us.ibm.com ([32.97.182.144]:54943 "EHLO e4.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753724AbZIPP5R (ORCPT ); Wed, 16 Sep 2009 11:57:17 -0400 Date: Wed, 16 Sep 2009 08:57:19 -0700 From: "Paul E. McKenney" To: Catalin Marinas Cc: Eric Sesterhenn , linux-kernel Subject: Re: RCU callbacks and TREE_PREEMPT_RCU Message-ID: <20090916155719.GA10588@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1253110641.31751.92.camel@pc1117.cambridge.arm.com> <20090916152929.GA6737@linux.vnet.ibm.com> <1253115255.31751.96.camel@pc1117.cambridge.arm.com> <20090916154716.GC6737@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090916154716.GC6737@linux.vnet.ibm.com> User-Agent: Mutt/1.5.15+20070412 (2007-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7870 Lines: 214 On Wed, Sep 16, 2009 at 08:47:16AM -0700, Paul E. McKenney wrote: > On Wed, Sep 16, 2009 at 04:34:15PM +0100, Catalin Marinas wrote: > > On Wed, 2009-09-16 at 08:29 -0700, Paul E. McKenney wrote: > > > On Wed, Sep 16, 2009 at 03:17:21PM +0100, Catalin Marinas wrote: > > > > When TREE_PREEMPT_RCU is enabled, the rcu list traversing above fails > > > > with access to 0x6b6b6b6b but it is fine with TREE_PREEMPT_RCU=n and > > > > TREE_RCU=y. During clean-up, kmemleak objects should no longer be freed > > > > by other means since kmemleak was disabled and all callbacks are > > > > ignored. The system is a 900Mhz P3, 256MB RAM, CONFIG_SMP=n. > > > > > > > > Is there something I'm doing wrong in kmemleak or a bug with RCU > > > > preemption? The kernel oops looks like this: > > > > > > From your description and the code above, I must suspect a bug with > > > RCU preemption. A new one, as the only bugs I am currently chasing > > > involve NR_CPUS>32 (>64 on 64-bit systems). > > > > > > CONFIG_SMP=n implies NR_CPUS==1 in your build, correct? > > > > CONFIG_NR_CPUS=1. > > I was afraid of that. ;-) PS to previous -- there -is- a bug in mainline for TREE_PREEMPT_RCU for single-CPU operation, but it is with synchronize_rcu() rather than call_rcu(). The fix is in tip/core/urgent, commit #366b04ca. Or see the following patch. So, could you please give the following patch a try? Thanx, Paul Commit-ID: 366b04ca60c70479e2959fe8485b87ff380fdbbf Gitweb: http://git.kernel.org/tip/366b04ca60c70479e2959fe8485b87ff380fdbbf Author: Paul E. McKenney AuthorDate: Sun, 13 Sep 2009 09:15:11 -0700 Committer: Ingo Molnar CommitDate: Tue, 15 Sep 2009 08:43:59 +0200 rcu: Fix synchronize_rcu() for TREE_PREEMPT_RCU The redirection of synchronize_sched() to synchronize_rcu() was appropriate for TREE_RCU, but not for TREE_PREEMPT_RCU. Fix this by creating an underlying synchronize_sched(). TREE_RCU then redirects synchronize_rcu() to synchronize_sched(), while TREE_PREEMPT_RCU has its own version of synchronize_rcu(). Signed-off-by: Paul E. McKenney Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu LKML-Reference: <12528585111916-git-send-email-> Signed-off-by: Ingo Molnar --- include/linux/rcupdate.h | 23 +++++------------------ include/linux/rcutree.h | 4 ++-- kernel/rcupdate.c | 44 +++++++++++++++++++++++++++++++++++++++++++- 3 files changed, 50 insertions(+), 21 deletions(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 95e0615..39dce83 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -52,8 +52,13 @@ struct rcu_head { }; /* Exported common interfaces */ +#ifdef CONFIG_TREE_PREEMPT_RCU extern void synchronize_rcu(void); +#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ +#define synchronize_rcu synchronize_sched +#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */ extern void synchronize_rcu_bh(void); +extern void synchronize_sched(void); extern void rcu_barrier(void); extern void rcu_barrier_bh(void); extern void rcu_barrier_sched(void); @@ -262,24 +267,6 @@ struct rcu_synchronize { extern void wakeme_after_rcu(struct rcu_head *head); /** - * synchronize_sched - block until all CPUs have exited any non-preemptive - * kernel code sequences. - * - * This means that all preempt_disable code sequences, including NMI and - * hardware-interrupt handlers, in progress on entry will have completed - * before this primitive returns. However, this does not guarantee that - * softirq handlers will have completed, since in some kernels, these - * handlers can run in process context, and can block. - * - * This primitive provides the guarantees made by the (now removed) - * synchronize_kernel() API. In contrast, synchronize_rcu() only - * guarantees that rcu_read_lock() sections will have completed. - * In "classic RCU", these two guarantees happen to be one and - * the same, but can differ in realtime RCU implementations. - */ -#define synchronize_sched() __synchronize_sched() - -/** * call_rcu - Queue an RCU callback for invocation after a grace period. * @head: structure to be used for queueing the RCU updates. * @func: actual update function to be invoked after the grace period diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index a893077..00d08c0 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -53,6 +53,8 @@ static inline void __rcu_read_unlock(void) preempt_enable(); } +#define __synchronize_sched() synchronize_rcu() + static inline void exit_rcu(void) { } @@ -68,8 +70,6 @@ static inline void __rcu_read_unlock_bh(void) local_bh_enable(); } -#define __synchronize_sched() synchronize_rcu() - extern void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu)); diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index bd5d5c8..28d2f24 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -74,6 +74,8 @@ void wakeme_after_rcu(struct rcu_head *head) complete(&rcu->completion); } +#ifdef CONFIG_TREE_PREEMPT_RCU + /** * synchronize_rcu - wait until a grace period has elapsed. * @@ -87,7 +89,7 @@ void synchronize_rcu(void) { struct rcu_synchronize rcu; - if (rcu_blocking_is_gp()) + if (!rcu_scheduler_active) return; init_completion(&rcu.completion); @@ -98,6 +100,46 @@ void synchronize_rcu(void) } EXPORT_SYMBOL_GPL(synchronize_rcu); +#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */ + +/** + * synchronize_sched - wait until an rcu-sched grace period has elapsed. + * + * Control will return to the caller some time after a full rcu-sched + * grace period has elapsed, in other words after all currently executing + * rcu-sched read-side critical sections have completed. These read-side + * critical sections are delimited by rcu_read_lock_sched() and + * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(), + * local_irq_disable(), and so on may be used in place of + * rcu_read_lock_sched(). + * + * This means that all preempt_disable code sequences, including NMI and + * hardware-interrupt handlers, in progress on entry will have completed + * before this primitive returns. However, this does not guarantee that + * softirq handlers will have completed, since in some kernels, these + * handlers can run in process context, and can block. + * + * This primitive provides the guarantees made by the (now removed) + * synchronize_kernel() API. In contrast, synchronize_rcu() only + * guarantees that rcu_read_lock() sections will have completed. + * In "classic RCU", these two guarantees happen to be one and + * the same, but can differ in realtime RCU implementations. + */ +void synchronize_sched(void) +{ + struct rcu_synchronize rcu; + + if (rcu_blocking_is_gp()) + return; + + init_completion(&rcu.completion); + /* Will wake me after RCU finished. */ + call_rcu_sched(&rcu.head, wakeme_after_rcu); + /* Wait for it. */ + wait_for_completion(&rcu.completion); +} +EXPORT_SYMBOL_GPL(synchronize_sched); + /** * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed. * -- 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/ -- 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/