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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 81F23C433FE for ; Mon, 18 Apr 2022 22:54:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233680AbiDRW5G (ORCPT ); Mon, 18 Apr 2022 18:57:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44354 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233256AbiDRW4t (ORCPT ); Mon, 18 Apr 2022 18:56:49 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C88A82CC9D; Mon, 18 Apr 2022 15:54:03 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 77511B81135; Mon, 18 Apr 2022 22:54:02 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3588FC385A8; Mon, 18 Apr 2022 22:54:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1650322441; bh=3/4SJxZl7LRSsaEhih4xR7lzgf/M6pQIEs1EAdF+8Xg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=t/MDb//Dx1aVAuwdSFZUrhtpeY5xRFXWDcqAFKG9dd54tI2v/+dDd+iUaG9JUUqLj gpUM8xB2YJpklamaW8j7k0VXsAFV3QePxlcNb9YMlZnWZb1jnuRXS3rVdv8TFL00zO KQaTFfBLM5xOOOtVUXVxSx/uWcgrv82TDyDTZKJ8GGjO7EPBxHIs7HCd3Ss5tw/Lcw KQ3kPD9x+7xMUG5ETaT/FVVVOEyLxJdV9Owk1LmBjyQ00cAmFHa4/N0siDX5fMtVYV yfsqpDZD+m+DJESF1aIRlwpQqQCtxx/rBYK2rNp6vQF5bfHKoxMDgKelyezv2VKCBI 045K4+Yqen8fA== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id E36075C0848; Mon, 18 Apr 2022 15:54:00 -0700 (PDT) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, rostedt@goodmis.org, "Paul E. McKenney" , Saravanan D Subject: [PATCH rcu 03/11] rcu: Check for jiffies going backwards Date: Mon, 18 Apr 2022 15:53:51 -0700 Message-Id: <20220418225359.3945217-3-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20220418225345.GA3945110@paulmck-ThinkPad-P17-Gen-1> References: <20220418225345.GA3945110@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org A report of a 12-jiffy normal RCU CPU stall warning raises interesting questions about the nature of time on the offending system. This commit instruments rcu_sched_clock_irq(), which is RCU's hook into the scheduling-clock interrupt, checking for the jiffies counter going backwards. Reported-by: Saravanan D Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 10 ++++++++++ kernel/rcu/tree.h | 1 + 2 files changed, 11 insertions(+) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index a4b8189455d5..a5ea67454640 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1679,6 +1679,8 @@ static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp) rdp->gp_seq = rnp->gp_seq; /* Remember new grace-period state. */ if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || rdp->gpwrap) WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed); + if (IS_ENABLED(CONFIG_PROVE_RCU) && READ_ONCE(rdp->gpwrap)) + WRITE_ONCE(rdp->last_sched_clock, jiffies); WRITE_ONCE(rdp->gpwrap, false); rcu_gpnum_ovf(rnp, rdp); return ret; @@ -2609,6 +2611,13 @@ static void rcu_do_batch(struct rcu_data *rdp) */ void rcu_sched_clock_irq(int user) { + unsigned long j; + + if (IS_ENABLED(CONFIG_PROVE_RCU)) { + j = jiffies; + WARN_ON_ONCE(time_before(j, __this_cpu_read(rcu_data.last_sched_clock))); + __this_cpu_write(rcu_data.last_sched_clock, j); + } trace_rcu_utilization(TPS("Start scheduler-tick")); lockdep_assert_irqs_disabled(); raw_cpu_inc(rcu_data.ticks_this_gp); @@ -4179,6 +4188,7 @@ rcu_boot_init_percpu_data(int cpu) rdp->rcu_ofl_gp_flags = RCU_GP_CLEANED; rdp->rcu_onl_gp_seq = rcu_state.gp_seq; rdp->rcu_onl_gp_flags = RCU_GP_CLEANED; + rdp->last_sched_clock = jiffies; rdp->cpu = cpu; rcu_boot_init_nocb_percpu_data(rdp); } diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 926673ebe355..94b55f669915 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -254,6 +254,7 @@ struct rcu_data { unsigned long rcu_onl_gp_seq; /* ->gp_seq at last online. */ short rcu_onl_gp_flags; /* ->gp_flags at last online. */ unsigned long last_fqs_resched; /* Time of last rcu_resched(). */ + unsigned long last_sched_clock; /* Jiffies of last rcu_sched_clock_irq(). */ int cpu; }; -- 2.31.1.189.g2e36527f23