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: Wed, 11 Aug 2010 15:00:47 -0700 Message-ID: <20100811220047.GH2516@linux.vnet.ibm.com> References: <1281471924-2237-1-git-send-email-linville@tuxdriver.com> <20100810204358.GA1076@gondor.apana.org.au> <20100810211932.GG2379@linux.vnet.ibm.com> <20100810.163117.241919476.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 e9.ny.us.ibm.com ([32.97.182.139]:49100 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751392Ab0HKWBA (ORCPT ); Wed, 11 Aug 2010 18:01:00 -0400 Received: from d01relay06.pok.ibm.com (d01relay06.pok.ibm.com [9.56.227.116]) by e9.ny.us.ibm.com (8.14.4/8.13.1) with ESMTP id o7BLhT52016260 for ; Wed, 11 Aug 2010 17:43:29 -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 o7BM0nTM1962200 for ; Wed, 11 Aug 2010 18:00:49 -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 o7BM0mbC015965 for ; Wed, 11 Aug 2010 18:00:49 -0400 Content-Disposition: inline In-Reply-To: <20100810.163117.241919476.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-ID: On Tue, Aug 10, 2010 at 04:31:17PM -0700, David Miller wrote: > From: "Paul E. McKenney" > Date: Tue, 10 Aug 2010 14:19:32 -0700 > > > Your suggestion of providing another API rcu_read_lock_irqsoff() > > and rcu_read_unlock_irqsoff() is the best I can think of right offhand. > > > > What tree/commit do you need the patch against? > > Linus's tree is fine for this. > > But we need this fix for 2.6.35-stable too. Herbert would > you object to putting John's more simple fix there? > > John, when referencing other commits in commit messages, > please provide the SHA1 ID as well as the commit message > header line. And here is an interim patch. I have queued a slightly different patch that takes advantage of the more sophisticated PROVE_RCU handling currently in -tip, but the API is the same, so code written against this patch will work against the upcoming patch. Thoughts? Thanx, Paul commit 8934f3fd1092b7ef6a1524e1d2356baeec9f330e 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..d159835 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