From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755445AbcK3B3O (ORCPT ); Tue, 29 Nov 2016 20:29:14 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:45691 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752694AbcK3B3G (ORCPT ); Tue, 29 Nov 2016 20:29:06 -0500 Date: Tue, 29 Nov 2016 17:28:17 -0800 From: "Paul E. McKenney" To: Guenter Roeck Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , sparclinux@vger.kernel.org, davem@davemloft.net Subject: Re: next: Commit 'mm: Prevent __alloc_pages_nodemask() RCU CPU stall ...' causing hang on sparc32 qemu Reply-To: paulmck@linux.vnet.ibm.com References: <20161129212308.GA12447@roeck-us.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161129212308.GA12447@roeck-us.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16113001-0024-0000-0000-0000152637D6 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006166; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000193; SDB=6.00787123; UDB=6.00380712; IPR=6.00564808; BA=6.00004928; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00013485; XFM=3.00000011; UTC=2016-11-30 01:28:19 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16113001-0025-0000-0000-0000468CE13D Message-Id: <20161130012817.GH3924@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-11-29_09:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1609300000 definitions=main-1611300016 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? 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) { }