Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756798AbbFPROS (ORCPT ); Tue, 16 Jun 2015 13:14:18 -0400 Received: from mail-pd0-f173.google.com ([209.85.192.173]:36330 "EHLO mail-pd0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756661AbbFPROK (ORCPT ); Tue, 16 Jun 2015 13:14:10 -0400 Message-ID: <55805960.2030008@plumgrid.com> Date: Tue, 16 Jun 2015 10:14:08 -0700 From: Alexei Starovoitov User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: paulmck@linux.vnet.ibm.com, Steven Rostedt CC: Daniel Wagner , LKML Subject: Re: call_rcu from trace_preempt References: <557F509D.2000509@plumgrid.com> <20150615230702.GB3913@linux.vnet.ibm.com> <557F7764.5060707@plumgrid.com> <20150616021458.GE3913@linux.vnet.ibm.com> <557FB7E1.6080004@plumgrid.com> <20150616122733.GG3913@linux.vnet.ibm.com> <20150616113738.3ab2667b@gandalf.local.home> <20150616160546.GL3913@linux.vnet.ibm.com> In-Reply-To: <20150616160546.GL3913@linux.vnet.ibm.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2260 Lines: 61 On 6/16/15 9:05 AM, Paul E. McKenney wrote: > On Tue, Jun 16, 2015 at 11:37:38AM -0400, Steven Rostedt wrote: >> On Tue, 16 Jun 2015 05:27:33 -0700 >> "Paul E. McKenney" wrote: >> >>> On Mon, Jun 15, 2015 at 10:45:05PM -0700, Alexei Starovoitov wrote: >>>> On 6/15/15 7:14 PM, Paul E. McKenney wrote: >>>>> >>>>> Why do you believe that it is better to fix it within call_rcu()? >>>> >>>> found it: >>>> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c >>>> index 8cf7304b2867..a3be09d482ae 100644 >>>> --- a/kernel/rcu/tree.c >>>> +++ b/kernel/rcu/tree.c >>>> @@ -935,9 +935,9 @@ bool notrace rcu_is_watching(void) >>>> { >>>> bool ret; >>>> >>>> - preempt_disable(); >>>> + preempt_disable_notrace(); >>>> ret = __rcu_is_watching(); >>>> - preempt_enable(); >>>> + preempt_enable_notrace(); >>>> return ret; >>>> } >>>> >>>> the rcu_is_watching() and __rcu_is_watching() are already marked >>>> notrace, so imo it's a good 'fix'. >>>> What was happening is that the above preempt_enable was triggering >>>> recursive call_rcu that was indeed messing 'rdp' that was >>>> prepared by __call_rcu and before __call_rcu_core could use that. >>> >>>> btw, also noticed that local_irq_save done by note_gp_changes >>>> is partially redundant. In __call_rcu_core path the irqs are >>>> already disabled. >>> >> >> If rcu_is_watching() and __rcu_is_watching() are both marked as >> notrace, it makes sense to use preempt_disable/enable_notrace() as it >> otherwise defeats the purpose of the notrace markers on rcu_is_watching. >> >> That is regardless of what the rest of this thread is about. > > Good enough! Alexei, are you OK with my adding your Signed-off-by > to the above patch? sure. Signed-off-by: Alexei Starovoitov > (Still not sold on reentrant call_rcu() and > kfree_rcu(), but getting notrace set up correctly is worthwhile.) I'm not sold on it either. So far trying to understand all consequences. -- 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/