From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH] netpoll: use non-BH variant of RCU Date: Thu, 12 Aug 2010 08:42:13 -0700 Message-ID: <20100812154213.GB2524@linux.vnet.ibm.com> References: <20100810211932.GG2379@linux.vnet.ibm.com> <20100810.163117.241919476.davem@davemloft.net> <20100811220047.GH2516@linux.vnet.ibm.com> <20100811.230936.183035599.davem@davemloft.net> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: herbert@gondor.apana.org.au, linville@tuxdriver.com, netdev@vger.kernel.org To: David Miller Return-path: Received: from e7.ny.us.ibm.com ([32.97.182.137]:38932 "EHLO e7.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933825Ab0HLPm1 (ORCPT ); Thu, 12 Aug 2010 11:42:27 -0400 Received: from d01relay06.pok.ibm.com (d01relay06.pok.ibm.com [9.56.227.116]) by e7.ny.us.ibm.com (8.14.4/8.13.1) with ESMTP id o7CFSlWG002283 for ; Thu, 12 Aug 2010 11:28:47 -0400 Received: from d01av04.pok.ibm.com (d01av04.pok.ibm.com [9.56.224.64]) by d01relay06.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id o7CFgE4o1798202 for ; Thu, 12 Aug 2010 11:42:14 -0400 Received: from d01av04.pok.ibm.com (loopback [127.0.0.1]) by d01av04.pok.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id o7CFgD03032105 for ; Thu, 12 Aug 2010 11:42:14 -0400 Content-Disposition: inline In-Reply-To: <20100811.230936.183035599.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, Aug 11, 2010 at 11:09:36PM -0700, David Miller wrote: > From: "Paul E. McKenney" > Date: Wed, 11 Aug 2010 15:00:47 -0700 > > > @@ -113,6 +113,12 @@ int rcu_my_thread_group_empty(void) > > return thread_group_empty(current); > > } > > EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty); > > + > > +void rcu_read_unlock_bh_irqsoff_check(void) > > +{ > > + WARN_ON_ONCE(in_irq() || irqs_disabled()); > > +} > > +EXPORT_SYMBOL_GPL(rcu_read_unlock_bh_irqsoff_check); > > #endif /* #ifdef CONFIG_PROVE_RCU */ > > Is this WARN_ON_ONCE() test inverted? It seems to be called where we > "should be" in an IRQ or have IRQs disabled. You are quite correct. (Beat head against wall.) :-/ ------------------------------------------------------------------------ #!/bin/bash for ((i=0;i<100;i++)) do echo "De Morgan when converting rcu_lockdep_assert() to WARN_ON_ONCE()" done ------------------------------------------------------------------------ This does sort of defeat the purpose of writing something 100 times, but I am after all a software developer!!! Thank you very much for catching this, and please see below for a replacement patch. Thanx, Paul commit 2c9ace45088a25b474167d04b416d279f4ea3401 Author: Paul E. McKenney Date: Wed Aug 11 14:54:33 2010 -0700 rcu: add rcu_read_lock_bh_irqsoff() and rcu_read_unlock_bh_irqsoff() The rcu_read_lock_bh() and rcu_read_unlock_bh() functions can no longer be used when interrupts are disabled due to new debug checks in the _local_bh_enable() function. This commit therefore supplies new functions that may only be called with either interrupts disabled or from interrupt handlers, and this is checked for under CONFIG_PROVE_RCU. Requested-by: Herbert Xu Signed-off-by: Paul E. McKenney diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 9fbc54a..08cdc58 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -270,10 +270,13 @@ extern int rcu_my_thread_group_empty(void); (p); \ }) +void rcu_read_unlock_bh_irqsoff_check(void); + #else /* #ifdef CONFIG_PROVE_RCU */ #define rcu_dereference_check(p, c) rcu_dereference_raw(p) #define rcu_dereference_protected(p, c) (p) +#define rcu_read_unlock_bh_irqsoff_check() do { } while (0) #endif /* #else #ifdef CONFIG_PROVE_RCU */ @@ -361,13 +364,13 @@ static inline void rcu_read_unlock(void) */ static inline void rcu_read_lock_bh(void) { - __rcu_read_lock_bh(); + local_bh_disable(); __acquire(RCU_BH); rcu_read_acquire_bh(); } /* - * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section + * rcu_read_unlock_bh() - marks the end of a softirq-only RCU critical section * * See rcu_read_lock_bh() for more information. */ @@ -375,7 +378,34 @@ static inline void rcu_read_unlock_bh(void) { rcu_read_release_bh(); __release(RCU_BH); - __rcu_read_unlock_bh(); + local_bh_enable(); +} + +/** + * rcu_read_lock_bh_irqsoff() - mark the beginning of an RCU-bh critical section + * + * This is equivalent of rcu_read_lock_bh(), but to be used where the + * caller either is in an irq handler or has irqs disabled. Note that + * this function assumes that PREEMPT_RT kernels run irq handlers at + * higher priority than softirq handlers! + */ +static inline void rcu_read_lock_bh_irqsoff(void) +{ + rcu_read_unlock_bh_irqsoff_check(); + __acquire(RCU_BH); + rcu_read_acquire_bh(); +} + +/* + * rcu_read_unlock_bh_irqsoff - marks the end of an RCU-bh critical section + * + * See rcu_read_lock_bh_irqsoff() for more information. + */ +static inline void rcu_read_unlock_bh_irqsoff(void) +{ + rcu_read_release_bh(); + __release(RCU_BH); + rcu_read_unlock_bh_irqsoff_check(); } /** diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index e2e8931..009c7f3 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -36,8 +36,6 @@ static inline void rcu_note_context_switch(int cpu) #define __rcu_read_lock() preempt_disable() #define __rcu_read_unlock() preempt_enable() -#define __rcu_read_lock_bh() local_bh_disable() -#define __rcu_read_unlock_bh() local_bh_enable() #define call_rcu_sched call_rcu #define rcu_init_sched() do { } while (0) diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index c0ed1c0..98b50d8 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -75,15 +75,6 @@ static inline int rcu_preempt_depth(void) #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */ -static inline void __rcu_read_lock_bh(void) -{ - local_bh_disable(); -} -static inline void __rcu_read_unlock_bh(void) -{ - local_bh_enable(); -} - extern void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu)); extern void synchronize_rcu_bh(void); diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index 4d16983..ae6ae40 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -113,6 +113,12 @@ int rcu_my_thread_group_empty(void) return thread_group_empty(current); } EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty); + +void rcu_read_unlock_bh_irqsoff_check(void) +{ + WARN_ON_ONCE(!in_irq() && !irqs_disabled()); +} +EXPORT_SYMBOL_GPL(rcu_read_unlock_bh_irqsoff_check); #endif /* #ifdef CONFIG_PROVE_RCU */ #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD