Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761123Ab3EBRf1 (ORCPT ); Thu, 2 May 2013 13:35:27 -0400 Received: from e37.co.us.ibm.com ([32.97.110.158]:52005 "EHLO e37.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754931Ab3EBRfY (ORCPT ); Thu, 2 May 2013 13:35:24 -0400 Date: Thu, 2 May 2013 10:32:57 -0700 From: "Paul E. McKenney" To: Julian Anastasov Cc: Peter Zijlstra , Simon Horman , Eric Dumazet , Ingo Molnar , lvs-devel@vger.kernel.org, netdev@vger.kernel.org, netfilter-devel@vger.kernel.org, linux-kernel@vger.kernel.org, Pablo Neira Ayuso , Dipankar Sarma Subject: Re: [PATCH v2 1/2] sched: Add cond_resched_rcu_lock() helper Message-ID: <20130502173257.GX3780@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1367290378-29224-2-git-send-email-horms@verge.net.au> <20130430072944.GA13959@verge.net.au> <20130501091012.GB28253@dyad.programming.kicks-ass.net> <20130501155501.GB7521@dyad.programming.kicks-ass.net> <20130502072623.GE7521@dyad.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13050217-7408-0000-0000-00000FC0BC30 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5648 Lines: 180 On Thu, May 02, 2013 at 06:54:05PM +0300, Julian Anastasov wrote: > > Hello, > > On Thu, 2 May 2013, Peter Zijlstra wrote: > > > On Wed, May 01, 2013 at 09:22:08PM +0300, Julian Anastasov wrote: > > > > +extern int __cond_resched_rcu(void); > > > > + > > > > +#define cond_resched_rcu() ({ \ > > > > + __might_sleep(__FILE__, __LINE__, 0); \ > > > > > > I see your goal. But digging into __might_sleep() > > > I see that rcu_sleep_check() will scream for the non-preempt > > > case because we are under rcu_read_lock. > > > > > > #ifdef CONFIG_PREEMPT_RCU > > #define PREEMPT_RCU_OFFSET 0 > > #else > > #define PREEMPT_RCU_OFFSET 1 > > #endif > > > > #define cond_resched_rcu() ({ \ > > __might_sleep(__FILE__, __LINE__, PREEMPT_RCU_OFFSET); \ > > __cond_resched_rcu(); \ > > }) > > > > Should work I think.. > > I implemented your idea. > > I tested the following patch in 2 variants, > TINY_RCU and CONFIG_TREE_PREEMPT_RCU. I see the Could you please also try CONFIG_TREE_RCU? > error if extra rcu_read_lock is added for testing. > > I'm using the PREEMPT_ACTIVE flag to indicate > that we are already under lock. It should work because > __might_sleep is not called with such bit. I also tried to > add new flag in include/linux/hardirq.h but PREEMPT_ACTIVE > depends on the arch, so this alternative looked difficult to > implement. > > include/linux/rcupdate.h | 7 ++++--- > include/linux/sched.h | 14 ++++++++++++++ > kernel/sched/core.c | 20 ++++++++++++++++++-- > 3 files changed, 36 insertions(+), 5 deletions(-) > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > index b758ce1..b594759 100644 > --- a/include/linux/rcupdate.h > +++ b/include/linux/rcupdate.h > @@ -480,9 +480,10 @@ static inline void rcu_preempt_sleep_check(void) > } > #endif /* #else #ifdef CONFIG_PROVE_RCU */ > > -#define rcu_sleep_check() \ > +#define rcu_sleep_check(locked) \ > do { \ > - rcu_preempt_sleep_check(); \ > + if (!(locked)) \ > + rcu_preempt_sleep_check(); \ > rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map), \ > "Illegal context switch in RCU-bh" \ > " read-side critical section"); \ > @@ -494,7 +495,7 @@ static inline void rcu_preempt_sleep_check(void) > #else /* #ifdef CONFIG_PROVE_RCU */ > > #define rcu_lockdep_assert(c, s) do { } while (0) > -#define rcu_sleep_check() do { } while (0) > +#define rcu_sleep_check(locked) do { } while (0) > > #endif /* #else #ifdef CONFIG_PROVE_RCU */ > > diff --git a/include/linux/sched.h b/include/linux/sched.h > index e692a02..027deea 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -2608,6 +2608,20 @@ extern int __cond_resched_softirq(void); > __cond_resched_softirq(); \ > }) > > +#ifdef CONFIG_PREEMPT_RCU > +#define PREEMPT_RCU_OFFSET 1 > +#else > +#define PREEMPT_RCU_OFFSET PREEMPT_CHECK_OFFSET > +#endif > + > +extern int __cond_resched_rcu(void); > + > +#define cond_resched_rcu() ({ \ > + __might_sleep(__FILE__, __LINE__, PREEMPT_ACTIVE | \ > + PREEMPT_RCU_OFFSET); \ > + __cond_resched_rcu(); \ > +}) > + > /* > * Does a critical section need to be broken due to another > * task waiting?: (technically does not depend on CONFIG_PREEMPT, > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 67d0465..2724be7 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -2793,7 +2793,7 @@ static inline void schedule_debug(struct task_struct *prev) > */ > if (unlikely(in_atomic_preempt_off() && !prev->exit_state)) > __schedule_bug(prev); > - rcu_sleep_check(); > + rcu_sleep_check(0); > > profile_hit(SCHED_PROFILING, __builtin_return_address(0)); > > @@ -4364,6 +4364,20 @@ int __sched __cond_resched_softirq(void) > } > EXPORT_SYMBOL(__cond_resched_softirq); > > +int __sched __cond_resched_rcu(void) > +{ > +#ifndef CONFIG_PREEMPT_RCU > + if (should_resched()) { > + rcu_read_unlock(); > + __cond_resched(); > + rcu_read_lock(); > + return 1; > + } > +#endif > + return 0; > +} > +EXPORT_SYMBOL(__cond_resched_rcu); > + > /** > * yield - yield the current processor to other threads. > * > @@ -7062,7 +7076,9 @@ void __might_sleep(const char *file, int line, int preempt_offset) > { > static unsigned long prev_jiffy; /* ratelimiting */ > > - rcu_sleep_check(); /* WARN_ON_ONCE() by default, no rate limit reqd. */ > + /* WARN_ON_ONCE() by default, no rate limit reqd. */ > + rcu_sleep_check(preempt_offset & PREEMPT_ACTIVE); Color me confused. >From what I can see, the two values passed in through preempt_offset are PREEMPT_LOCK_OFFSET and SOFTIRQ_DISABLE_OFFSET. PREEMPT_ACTIVE is normally a high-order bit, above PREEMPT_MASK, SOFTIRQ_MASK, and HARDIRQ_MASK. PREEMPT_LOCK_OFFSET and SOFTIRQ_DISABLE_OFFSET have only low-order bits, so I don't see how rcu_sleep_check() is passed anything other than zero. Am I going blind, or what? Thanx, Paul > + preempt_offset &= ~PREEMPT_ACTIVE; > if ((preempt_count_equals(preempt_offset) && !irqs_disabled()) || > system_state != SYSTEM_RUNNING || oops_in_progress) > return; > -- > 1.7.3.4 > > > Regards > > -- > Julian Anastasov > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- 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/