From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754592AbcK3Edy (ORCPT ); Tue, 29 Nov 2016 23:33:54 -0500 Received: from bh-25.webhostbox.net ([208.91.199.152]:60231 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751952AbcK3Edp (ORCPT ); Tue, 29 Nov 2016 23:33:45 -0500 Subject: Re: next: Commit 'mm: Prevent __alloc_pages_nodemask() RCU CPU stall ...' causing hang on sparc32 qemu To: paulmck@linux.vnet.ibm.com References: <20161129212308.GA12447@roeck-us.net> <20161130012817.GH3924@linux.vnet.ibm.com> Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , sparclinux@vger.kernel.org, davem@davemloft.net From: Guenter Roeck Message-ID: Date: Tue, 29 Nov 2016 20:32:51 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 MIME-Version: 1.0 In-Reply-To: <20161130012817.GH3924@linux.vnet.ibm.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Authenticated_sender: linux@roeck-us.net X-OutGoing-Spam-Status: No, score=-1.0 X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - bh-25.webhostbox.net X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - roeck-us.net X-Get-Message-Sender-Via: bh-25.webhostbox.net: authenticated_id: linux@roeck-us.net X-Authenticated-Sender: bh-25.webhostbox.net: linux@roeck-us.net X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/29/2016 05:28 PM, Paul E. McKenney wrote: > On Tue, Nov 29, 2016 at 01:23:08PM -0800, Guenter Roeck wrote: >> Hi Paul, >> >> most of my qemu tests for sparc32 targets started to fail in next-20161129. >> The problem is only seen in SMP builds; non-SMP builds are fine. >> Bisect points to commit 2d66cccd73436 ("mm: Prevent __alloc_pages_nodemask() >> RCU CPU stall warnings"); reverting that commit fixes the problem. >> >> Test scripts are available at: >> https://github.com/groeck/linux-build-test/tree/master/rootfs/sparc >> Test results are at: >> https://github.com/groeck/linux-build-test/tree/master/rootfs/sparc >> >> Bisect log is attached. >> >> Please let me know if there is anything I can do to help tracking down the >> problem. > > Apologies!!! Does the patch below help? > No, sorry, it doesn't make a difference. Guenter > Thanx, Paul > > ------------------------------------------------------------------------ > > commit 97708e737e2a55fed4bdbc005bf05ea909df6b73 > Author: Paul E. McKenney > Date: Tue Nov 29 11:06:05 2016 -0800 > > rcu: Allow boot-time use of cond_resched_rcu_qs() > > The cond_resched_rcu_qs() macro is used to force RCU quiescent states into > long-running in-kernel loops. However, some of these loops can execute > during early boot when interrupts are disabled, and during which time > it is therefore illegal to enter the scheduler. This commit therefore > makes cond_resched_rcu_qs() be a no-op during early boot. > > Signed-off-by: Paul E. McKenney > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > index 525ca34603b7..b6944cc19a07 100644 > --- a/include/linux/rcupdate.h > +++ b/include/linux/rcupdate.h > @@ -423,7 +423,7 @@ extern struct srcu_struct tasks_rcu_exit_srcu; > */ > #define cond_resched_rcu_qs() \ > do { \ > - if (!cond_resched()) \ > + if (!is_idle_task(current) && !cond_resched()) \ > rcu_note_voluntary_context_switch(current); \ > } while (0) > > diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h > index 7232d199a81c..20f5990deeee 100644 > --- a/include/linux/rcutiny.h > +++ b/include/linux/rcutiny.h > @@ -228,6 +228,7 @@ static inline void exit_rcu(void) > extern int rcu_scheduler_active __read_mostly; > void rcu_scheduler_starting(void); > #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ > +#define rcu_scheduler_active false > static inline void rcu_scheduler_starting(void) > { > } > >