From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754242AbeDWCfg (ORCPT ); Sun, 22 Apr 2018 22:35:36 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:59630 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753929AbeDWCbV (ORCPT ); Sun, 22 Apr 2018 22:31:21 -0400 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel.opensrc@gmail.com, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 03/22] rcu: Don't allocate rcu_nocb_mask if no one needs it Date: Sun, 22 Apr 2018 19:32:08 -0700 X-Mailer: git-send-email 2.5.2 In-Reply-To: <20180423023150.GA21533@linux.vnet.ibm.com> References: <20180423023150.GA21533@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 18042302-0052-0000-0000-000002E0B1C0 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008903; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000257; SDB=6.01021888; UDB=6.00521536; IPR=6.00801123; MB=3.00020719; MTD=3.00000008; XFM=3.00000015; UTC=2018-04-23 02:31:18 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18042302-0053-0000-0000-00005C6D822B Message-Id: <1524450747-22778-3-git-send-email-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-04-23_01:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=1 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1804230025 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit 44c65ff2e3b0 ("rcu: Eliminate NOCBs CPU-state Kconfig options") made allocation of rcu_nocb_mask depend only on the rcu_nocbs=, nohz_full=, or isolcpus= kernel boot parameters. However, it failed to change the initial value of rcu_init_nohz()'s local variable need_rcu_nocb_mask to false, which can result in useless allocation of an all-zero rcu_nocb_mask. This commit therefore fixes this bug by changing the initial value of need_rcu_nocb_mask to false. While we are in the area, also correct the error message that is printed when someone specifies that can-never-exist CPUs should be NOCBs CPUs. Reported-by: Byungchul Park Signed-off-by: Paul E. McKenney Acked-by: Byungchul Park --- kernel/rcu/tree_plugin.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 6c5df18bbf2f..3566e4f6dfcc 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -2283,7 +2283,7 @@ static void do_nocb_deferred_wakeup(struct rcu_data *rdp) void __init rcu_init_nohz(void) { int cpu; - bool need_rcu_nocb_mask = true; + bool need_rcu_nocb_mask = false; struct rcu_state *rsp; #if defined(CONFIG_NO_HZ_FULL) @@ -2306,7 +2306,7 @@ void __init rcu_init_nohz(void) #endif /* #if defined(CONFIG_NO_HZ_FULL) */ if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) { - pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n"); + pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n"); cpumask_and(rcu_nocb_mask, cpu_possible_mask, rcu_nocb_mask); } -- 2.5.2