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[209.132.180.67]) by mx.google.com with ESMTP id h19si428551plr.67.2018.12.12.18.17.40; Wed, 12 Dec 2018 18:17:55 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=intel.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726626AbeLMCPn convert rfc822-to-8bit (ORCPT + 99 others); Wed, 12 Dec 2018 21:15:43 -0500 Received: from mga03.intel.com ([134.134.136.65]:37204 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726526AbeLMCPm (ORCPT ); Wed, 12 Dec 2018 21:15:42 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by orsmga103.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 12 Dec 2018 18:15:41 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,347,1539673200"; d="scan'208";a="129494241" Received: from fmsmsx106.amr.corp.intel.com ([10.18.124.204]) by fmsmga001.fm.intel.com with ESMTP; 12 Dec 2018 18:15:41 -0800 Received: from shsmsx102.ccr.corp.intel.com (10.239.4.154) by FMSMSX106.amr.corp.intel.com (10.18.124.204) with Microsoft SMTP Server (TLS) id 14.3.408.0; Wed, 12 Dec 2018 18:15:41 -0800 Received: from shsmsx104.ccr.corp.intel.com ([169.254.5.203]) by shsmsx102.ccr.corp.intel.com ([169.254.2.182]) with mapi id 14.03.0415.000; Thu, 13 Dec 2018 10:11:35 +0800 From: "Zhang, Jun" To: "paulmck@linux.ibm.com" , "He, Bo" CC: Steven Rostedt , "linux-kernel@vger.kernel.org" , "josh@joshtriplett.org" , "mathieu.desnoyers@efficios.com" , "jiangshanlai@gmail.com" , "Xiao, Jin" , "Zhang, Yanmin" , "Bai, Jie A" , "Sun, Yi J" Subject: RE: rcu_preempt caused oom Thread-Topic: rcu_preempt caused oom Thread-Index: AdSHvQIr70OYynHSTxKgLAvVXX+0Zv//yKOAgAAWeAD//li4UIADPhuAgAAJSYD//3lRYIAAoJ4A//tcRfABJU8zAP/+T9Nw//xa4AD/91m7QP/uoBSA/9vB3nD/t3F+AP9tcGAw/tr6woD9snCZgPtjpC6Q9sakFQDtjQLogNsYI6iwtjC+vgDsYEklwNjA58YAsYF15gDjAkI/QMYE+T8AjAlMjtA= Date: Thu, 13 Dec 2018 02:11:35 +0000 Message-ID: <88DC34334CA3444C85D647DBFA962C2735AD5F77@SHSMSX104.ccr.corp.intel.com> References: <20181209195601.GA7854@linux.ibm.com> <20181211003838.GD4170@linux.ibm.com> <20181211044631.GA19942@linux.ibm.com> <20181212022446.GV4170@linux.ibm.com> <20181212154224.GX4170@linux.ibm.com> <20181212210316.GA14777@linux.ibm.com> <20181213001214.GE4170@linux.ibm.com> In-Reply-To: <20181213001214.GE4170@linux.ibm.com> Accept-Language: zh-CN, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-titus-metadata-40: eyJDYXRlZ29yeUxhYmVscyI6IiIsIk1ldGFkYXRhIjp7Im5zIjoiaHR0cDpcL1wvd3d3LnRpdHVzLmNvbVwvbnNcL0ludGVsMyIsImlkIjoiMjM4MTUxYzItNzVmMC00ZTBiLThjNjQtNTU2MGFhZmM2ZDZhIiwicHJvcHMiOlt7Im4iOiJDVFBDbGFzc2lmaWNhdGlvbiIsInZhbHMiOlt7InZhbHVlIjoiQ1RQX05UIn1dfV19LCJTdWJqZWN0TGFiZWxzIjpbXSwiVE1DVmVyc2lvbiI6IjE3LjEwLjE4MDQuNDkiLCJUcnVzdGVkTGFiZWxIYXNoIjoicXo2K1ZUYU5Nd0dMRDZSUlFSNUhBc2V0eG9hR3ZGUTlUb1FacE9OaG5mRzhsZjBYYmZ6RXpKQXpvUDJIa2lEeCJ9 x-ctpclassification: CTP_NT dlp-product: dlpe-windows dlp-version: 11.0.400.15 dlp-reaction: no-action x-originating-ip: [10.239.127.40] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, Paul I think the next patch is better. Because ULONG_CMP_GE could cause double write, which has risk that write back old value. Please help review. I don't test it. If you agree, we will test it. Thanks! diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 0b760c1..c00f34e 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1849,7 +1849,7 @@ static bool __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp, zero_cpu_stall_ticks(rdp); } rdp->gp_seq = rnp->gp_seq; /* Remember new grace-period state. */ - if (ULONG_CMP_GE(rnp->gp_seq_needed, rdp->gp_seq_needed) || rdp->gpwrap) + if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || rdp->gpwrap) rdp->gp_seq_needed = rnp->gp_seq_needed; WRITE_ONCE(rdp->gpwrap, false); rcu_gpnum_ovf(rnp, rdp); -----Original Message----- From: Paul E. McKenney [mailto:paulmck@linux.ibm.com] Sent: Thursday, December 13, 2018 08:12 To: He, Bo Cc: Steven Rostedt ; linux-kernel@vger.kernel.org; josh@joshtriplett.org; mathieu.desnoyers@efficios.com; jiangshanlai@gmail.com; Zhang, Jun ; Xiao, Jin ; Zhang, Yanmin ; Bai, Jie A ; Sun, Yi J Subject: Re: rcu_preempt caused oom On Wed, Dec 12, 2018 at 11:13:22PM +0000, He, Bo wrote: > I don't see the rcutree.sysrq_rcu parameter in v4.19 kernel, I also checked the latest kernel and the latest tag v4.20-rc6, not see the sysrq_rcu. > Please correct me if I have something wrong. That would be because I sent you the wrong patch, apologies! :-/ Please instead see the one below, which does add sysrq_rcu. Thanx, Paul > -----Original Message----- > From: Paul E. McKenney > Sent: Thursday, December 13, 2018 5:03 AM > To: He, Bo > Cc: Steven Rostedt ; > linux-kernel@vger.kernel.org; josh@joshtriplett.org; > mathieu.desnoyers@efficios.com; jiangshanlai@gmail.com; Zhang, Jun > ; Xiao, Jin ; Zhang, Yanmin > ; Bai, Jie A > Subject: Re: rcu_preempt caused oom > > On Wed, Dec 12, 2018 at 07:42:24AM -0800, Paul E. McKenney wrote: > > On Wed, Dec 12, 2018 at 01:21:33PM +0000, He, Bo wrote: > > > we reproduce on two boards, but I still not see the show_rcu_gp_kthreads() dump logs, it seems the patch can't catch the scenario. > > > I double confirmed the CONFIG_PROVE_RCU=y is enabled in the config as it's extracted from the /proc/config.gz. > > > > Strange. > > > > Are the systems responsive to sysrq keys once failure occurs? If > > so, I will provide you a sysrq-R or some such to dump out the RCU state. > > Or, as it turns out, sysrq-y if booting with rcutree.sysrq_rcu=1 using the patch below. Only lightly tested. ------------------------------------------------------------------------ commit 04b6245c8458e8725f4169e62912c1fadfdf8141 Author: Paul E. McKenney Date: Wed Dec 12 16:10:09 2018 -0800 rcu: Add sysrq rcu_node-dump capability Backported from v4.21/v5.0 Life is hard if RCU manages to get stuck without triggering RCU CPU stall warnings or triggering the rcu_check_gp_start_stall() checks for failing to start a grace period. This commit therefore adds a boot-time-selectable sysrq key (commandeering "y") that allows manually dumping Tree RCU state. The new rcutree.sysrq_rcu kernel boot parameter must be set for this sysrq to be available. Signed-off-by: Paul E. McKenney diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 0b760c1369f7..e9392a9d6291 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -61,6 +61,7 @@ #include #include #include +#include #include "tree.h" #include "rcu.h" @@ -128,6 +129,9 @@ int num_rcu_lvl[] = NUM_RCU_LVL_INIT; int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */ /* panic() on RCU Stall sysctl. */ int sysctl_panic_on_rcu_stall __read_mostly; +/* Commandeer a sysrq key to dump RCU's tree. */ static bool sysrq_rcu; +module_param(sysrq_rcu, bool, 0444); /* * The rcu_scheduler_active variable is initialized to the value @@ -662,6 +666,27 @@ void show_rcu_gp_kthreads(void) } EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads); +/* Dump grace-period-request information due to commandeered sysrq. */ +static void sysrq_show_rcu(int key) { + show_rcu_gp_kthreads(); +} + +static struct sysrq_key_op sysrq_rcudump_op = { + .handler = sysrq_show_rcu, + .help_msg = "show-rcu(y)", + .action_msg = "Show RCU tree", + .enable_mask = SYSRQ_ENABLE_DUMP, +}; + +static int __init rcu_sysrq_init(void) +{ + if (sysrq_rcu) + return register_sysrq_key('y', &sysrq_rcudump_op); + return 0; +} +early_initcall(rcu_sysrq_init); + /* * Send along grace-period-related data for rcutorture diagnostics. */