From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753147AbcJKN3F (ORCPT ); Tue, 11 Oct 2016 09:29:05 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:40487 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750846AbcJKN3D (ORCPT ); Tue, 11 Oct 2016 09:29:03 -0400 Date: Tue, 11 Oct 2016 06:28:49 -0700 From: "Paul E. McKenney" To: riel@redhat.com Cc: linux-kernel@vger.kernel.org Subject: Untested patch to recheck idle state for expedited grace periods Reply-To: paulmck@linux.vnet.ibm.com MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16101113-0012-0000-0000-000010DB4F64 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00005892; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000186; SDB=6.00766922; UDB=6.00366883; IPR=6.00543062; BA=6.00004801; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00012948; XFM=3.00000011; UTC=2016-10-11 13:28:40 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16101113-0013-0000-0000-0000463662D2 Message-Id: <20161011132849.GA21962@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-10-11_08:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=1 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1609300000 definitions=main-1610110233 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, Rik, And it turns out that I did not in fact do the recheck at IPI time. The (untested) patch below is an alleged fix. Thoughts? Thanx, Paul ------------------------------------------------------------------------ commit e53e0b3e7b3c783962f9461bcb9aa8bc3e3a8688 Author: Paul E. McKenney Date: Tue Oct 11 06:09:59 2016 -0700 rcu: Make expedited grace periods recheck dyntick idle state Expedited grace periods check dyntick-idle state, and avoid sending IPIs to idle CPUs, including those running guest OSes, and, on NOHZ_FULL kernels, nohz_full CPUs. However, the kernel has been observed checking a CPU while it was non-idle, but sending the IPI after it has gone idle. This commit therefore rechecks idle state immediately before sending the IPI, refraining from IPIing CPUs that have since gone idle. Reported-by: Rik van Riel Signed-off-by: Paul E. McKenney diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index e99a5234d9ed..fe98dd24adf8 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -404,6 +404,7 @@ struct rcu_data { atomic_long_t exp_workdone1; /* # done by others #1. */ atomic_long_t exp_workdone2; /* # done by others #2. */ atomic_long_t exp_workdone3; /* # done by others #3. */ + int exp_dynticks_snap; /* Double-check need for IPI. */ /* 7) Callback offloading. */ #ifdef CONFIG_RCU_NOCB_CPU diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 24343eb87b58..d3053e99fdb6 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -358,8 +358,10 @@ static void sync_rcu_exp_select_cpus(struct rcu_state *rsp, struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); + rdp->exp_dynticks_snap = + atomic_add_return(0, &rdtp->dynticks); if (raw_smp_processor_id() == cpu || - !(atomic_add_return(0, &rdtp->dynticks) & 0x1) || + !(rdp->exp_dynticks_snap & 0x1) || !(rnp->qsmaskinitnext & rdp->grpmask)) mask_ofl_test |= rdp->grpmask; } @@ -377,9 +379,17 @@ static void sync_rcu_exp_select_cpus(struct rcu_state *rsp, /* IPI the remaining CPUs for expedited quiescent state. */ for_each_leaf_node_possible_cpu(rnp, cpu) { unsigned long mask = leaf_node_cpu_bit(rnp, cpu); + struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); + struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); + if (!(mask_ofl_ipi & mask)) continue; retry_ipi: + if (atomic_add_return(0, &rdtp->dynticks) != + rdp->exp_dynticks_snap) { + mask_ofl_test |= mask; + continue; + } ret = smp_call_function_single(cpu, func, rsp, 0); if (!ret) { mask_ofl_ipi &= ~mask;