From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B7254C2BB85 for ; Wed, 15 Apr 2020 17:24:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 98D9520857 for ; Wed, 15 Apr 2020 17:24:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586971456; bh=9cWNvOBuFtO8wYiz1liQufquRY7A6S1vBnbO0MsNQc0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=2nap9WHaWPks8EFCKfLCECeCDlHOLdeM6lTBxboAjDDvADQ3uVPFsMgDPpfnZH4P6 SxlTv/BrpRmKQd3eEL72SQ1X3u289s/jUNf+/ZLrGpCnSv8Q2qObTDWvPPrz2CYbG2 IUiojtn4vDB6Mh0/MBXBEaG10hYoDAY2CrbyU+NA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2410931AbgDORYI (ORCPT ); Wed, 15 Apr 2020 13:24:08 -0400 Received: from mail.kernel.org ([198.145.29.99]:37960 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2410925AbgDORYG (ORCPT ); Wed, 15 Apr 2020 13:24:06 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7D4D0214D8; Wed, 15 Apr 2020 17:24:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586971445; bh=9cWNvOBuFtO8wYiz1liQufquRY7A6S1vBnbO0MsNQc0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=dXP68iJ4/qV/M3FTgCGy/tzz7ut/Ys4t9szYIKe9Wc4h8T0cMQMEEVBMB9/PqIEEQ pogxY9/8tlJbQ2w1cERuMHw/wPkBEHx439IJbWvz+juE4j9BcgIebQeQJE5p+gt+qA c/8buwdwNamYMhCrpwS6lRm5uCqAP0Zr2jhx/YD0= From: paulmck@kernel.org To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, 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@joelfernandes.org, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 2/3] rcu: When GP kthread is starved, tag idle threads as false positives Date: Wed, 15 Apr 2020 10:24:02 -0700 Message-Id: <20200415172403.9647-2-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20200415172341.GA9519@paulmck-ThinkPad-P72> References: <20200415172341.GA9519@paulmck-ThinkPad-P72> Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org From: "Paul E. McKenney" If the grace-period kthread is starved, idle threads' extended quiescent states are not reported. These idle threads thus wrongly appear to be blocking the current grace period. This commit therefore tags such idle threads as probable false positives when the grace-period kthread is being starved. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree_stall.h | 24 +++++++++++++++++++----- 1 file changed, 19 insertions(+), 5 deletions(-) diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index 119ed6a..4da41a6 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -299,6 +299,16 @@ static const char *gp_state_getname(short gs) return gp_state_names[gs]; } +/* Is the RCU grace-period kthread being starved of CPU time? */ +static bool rcu_is_gp_kthread_starving(unsigned long *jp) +{ + unsigned long j = jiffies - READ_ONCE(rcu_state.gp_activity); + + if (jp) + *jp = j; + return j > 2 * HZ; +} + /* * Print out diagnostic information for the specified stalled CPU. * @@ -313,6 +323,7 @@ static const char *gp_state_getname(short gs) static void print_cpu_stall_info(int cpu) { unsigned long delta; + bool falsepositive; char fast_no_hz[72]; struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); char *ticks_title; @@ -333,7 +344,9 @@ static void print_cpu_stall_info(int cpu) } print_cpu_stall_fast_no_hz(fast_no_hz, cpu); delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq); - pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld %s\n", + falsepositive = rcu_is_gp_kthread_starving(NULL) && + rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp)); + pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld %s%s\n", cpu, "O."[!!cpu_online(cpu)], "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)], @@ -345,8 +358,9 @@ static void print_cpu_stall_info(int cpu) rcu_dynticks_snap(rdp) & 0xfff, rdp->dynticks_nesting, rdp->dynticks_nmi_nesting, rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu), - READ_ONCE(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart, - fast_no_hz); + data_race(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart, + fast_no_hz, + falsepositive ? " (false positive?)" : ""); } /* Complain about starvation of grace-period kthread. */ @@ -355,8 +369,7 @@ static void rcu_check_gp_kthread_starvation(void) struct task_struct *gpk = rcu_state.gp_kthread; unsigned long j; - j = jiffies - READ_ONCE(rcu_state.gp_activity); - if (j > 2 * HZ) { + if (rcu_is_gp_kthread_starving(&j)) { pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#lx ->cpu=%d\n", rcu_state.name, j, (long)rcu_seq_current(&rcu_state.gp_seq), @@ -364,6 +377,7 @@ static void rcu_check_gp_kthread_starvation(void) gp_state_getname(rcu_state.gp_state), rcu_state.gp_state, gpk ? gpk->state : ~0, gpk ? task_cpu(gpk) : -1); if (gpk) { + pr_err("\tUnless %s kthread gets sufficient CPU time, OOM is now expected behavior.\n", rcu_state.name); pr_err("RCU grace-period kthread stack dump:\n"); sched_show_task(gpk); wake_up_process(gpk); -- 2.9.5