Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757203Ab0F3T7V (ORCPT ); Wed, 30 Jun 2010 15:59:21 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:60940 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754494Ab0F3T7U (ORCPT ); Wed, 30 Jun 2010 15:59:20 -0400 Date: Wed, 30 Jun 2010 12:58:53 -0700 From: Andrew Morton To: Peter Zijlstra Cc: Sergey Senozhatsky , Arjan van de Ven , "Rafael J. Wysocki" , Maxim Levitsky , Len Brown , Pavel Machek , Jiri Slaby , linux-pm@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Thomas Gleixner Subject: Re: [PATCH] cpuidle: avoid using smp_processor_id() in preemptible code (nr_iowait_cpu) v4 Message-Id: <20100630125853.245e6b99.akpm@linux-foundation.org> In-Reply-To: <1277476773.32034.639.camel@twins> References: <20100614140941.GA3581@swordfish.minsk.epam.com> <20100614073853.6fa2f91f@infradead.org> <20100614145439.GA3448@swordfish.minsk.epam.com> <20100614080154.7d6a71fc@infradead.org> <20100614151735.GB3448@swordfish.minsk.epam.com> <20100614204021.52c50cdc@infradead.org> <20100615061927.GA3312@swordfish> <20100615072435.5a47d850@infradead.org> <20100615145029.GB3967@swordfish.minsk.epam.com> <20100615080808.6286448b@infradead.org> <20100617062950.GA3979@swordfish> <1277476773.32034.639.camel@twins> X-Mailer: Sylpheed 2.4.8 (GTK+ 2.12.9; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2541 Lines: 68 On Fri, 25 Jun 2010 16:39:33 +0200 Peter Zijlstra wrote: > On Thu, 2010-06-17 at 09:29 +0300, Sergey Senozhatsky wrote: > > Fix > > > > BUG: using smp_processor_id() in preemptible [00000000] code: s2disk/3392 > > > The initial fix was to use get_cpu/put_cpu in nr_iowait_cpu. However, > > Arjan stated that "the bug is that it needs to be nr_iowait_cpu(int cpu)". > > > > This patch introduces nr_iowait_cpu(int cpu) and changes to its callers. > > > > Arjan also pointed out that we can't use get_cpu/put_cpu in update_ts_time_stats > > since we "pick the current cpu, rather than the one denoted by ts" in that case. > > To match given *ts and cpu denoted by *ts we use new field in the struct tick_sched: int cpu. > > > > diff --git a/include/linux/tick.h b/include/linux/tick.h > > index b232ccc..db14691 100644 > > --- a/include/linux/tick.h > > +++ b/include/linux/tick.h > > @@ -51,6 +51,7 @@ struct tick_sched { > > unsigned long check_clocks; > > enum tick_nohz_mode nohz_mode; > > ktime_t idle_tick; > > + int cpu; > > int inidle; > > int tick_stopped; > > unsigned long idle_jiffies; > > > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > > index 1d7b9bc..1907037 100644 > > --- a/kernel/time/tick-sched.c > > +++ b/kernel/time/tick-sched.c > > @@ -38,6 +38,9 @@ static ktime_t last_jiffies_update; > > > > struct tick_sched *tick_get_tick_sched(int cpu) > > { > > + /*FIXME: Arjan van de Ven: > > + can we do this bit once, when the ts structure gets initialized?*/ > > + per_cpu(tick_cpu_sched, cpu).cpu = cpu; > > return &per_cpu(tick_cpu_sched, cpu); > > } > > > @@ -161,7 +164,7 @@ update_ts_time_stats(struct tick_sched *ts, ktime_t now, u64 *last_update_time) > > if (ts->idle_active) { > > delta = ktime_sub(now, ts->idle_entrytime); > > ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta); > > - if (nr_iowait_cpu() > 0) > > + if (nr_iowait_cpu(ts->cpu) > 0) > > ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta); > > ts->idle_entrytime = now; > > } > > > This all seems extremely silly, why not something like: Does it work? c'mon guys, it's taking us weeks and weeks to fix one simple bug. It's a regression! We should be in panic mode. -- 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/