From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932798Ab3EBSyx (ORCPT ); Thu, 2 May 2013 14:54:53 -0400 Received: from ja.ssi.bg ([178.16.129.10]:46086 "EHLO ja.ssi.bg" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1760889Ab3EBSyv (ORCPT ); Thu, 2 May 2013 14:54:51 -0400 Date: Thu, 2 May 2013 21:55:54 +0300 (EEST) From: Julian Anastasov To: "Paul E. McKenney" 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 In-Reply-To: <20130502173257.GX3780@linux.vnet.ibm.com> Message-ID: 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> <20130502173257.GX3780@linux.vnet.ibm.com> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On Thu, 2 May 2013, Paul E. McKenney wrote: > On Thu, May 02, 2013 at 06:54:05PM +0300, Julian Anastasov wrote: > > > > 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? Note that I'm testing on some 9-year old UP system, i.e. 1 CPU. Now I enabled SMP to test CONFIG_TREE_RCU and the results are same. I think, it should be just like the TINY_RCU in terms of these debuggings (non-preempt). Extra rcu_read_lock gives me "Illegal context switch in RCU read-side critical section" in addition to the "BUG: sleeping function called from invalid context" message. > > 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. > > +extern int __cond_resched_rcu(void); > > + > > +#define cond_resched_rcu() ({ \ > > + __might_sleep(__FILE__, __LINE__, PREEMPT_ACTIVE | \ > > + PREEMPT_RCU_OFFSET); \ > > + __cond_resched_rcu(); \ > > +}) > > + > > @@ -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? Only the new cond_resched_rcu() macro provides PREEMPT_ACTIVE flag to skip the rcu_preempt_sleep_check() call. The old macros provide locked=0 as you noticed. Does it answer your question or I'm missing something? Regards -- Julian Anastasov