From nobody Tue Apr 7 23:59:43 2026 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 CD10CC4332F for ; Mon, 14 Nov 2022 23:28:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230212AbiKNX2l (ORCPT ); Mon, 14 Nov 2022 18:28:41 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39900 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236173AbiKNX2d (ORCPT ); Mon, 14 Nov 2022 18:28:33 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7C0691157 for ; Mon, 14 Nov 2022 15:28:29 -0800 (PST) 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 dfw.source.kernel.org (Postfix) with ESMTPS id 7E4EB614B9 for ; Mon, 14 Nov 2022 23:28:29 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DE716C433D7; Mon, 14 Nov 2022 23:28:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1668468508; bh=KYiqFd5L+cDLkyT6epEDOfkYEWTRr614tu/0hHbUz6U=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=A/X+O8aXEOSxP8x3DYS+35d+nm6T3IXGs6J4bGbc9VfVQJy6ELwhDCbAljCbdcbW+ Ya5GV1QLglrEjUrSTQZIv6iqQxhsq0oyu7YU/sNFM7Gw+9kVv/ShrNhJoovoAOcZH0 5uDZXAVidcgeYyG2M8Ey/jRi0JwE4Pmjk9a46yFg6Cj+6EHyfMYQJFxKiArml6sDHY TQAeKK6DnJnLxNRN5rUd+GHXuMV7vRPOyMhCZ/utvlTHSTX5aBElinuRp/lAQLkaO7 YeySi0M0Dlq8AeCCEeZtOjQXttBbN3owtuSf7eOnLeTrmeqPViADFlD4VDtkTAsIXa N9YdWvJoIzvKQ== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 8F9315C14FC; Mon, 14 Nov 2022 15:28:28 -0800 (PST) From: "Paul E. McKenney" To: tglx@linutronix.de Cc: linux-kernel@vger.kernel.org, john.stultz@linaro.org, sboyd@kernel.org, corbet@lwn.net, Mark.Rutland@arm.com, maz@kernel.org, kernel-team@meta.com, neeraju@codeaurora.org, ak@linux.intel.com, feng.tang@intel.com, zhengjun.xing@intel.com, "Paul E. McKenney" , Chris Mason , John Stultz , Waiman Long Subject: [PATCH clocksource 1/3] clocksource: Reject bogus watchdog clocksource measurements Date: Mon, 14 Nov 2022 15:28:24 -0800 Message-Id: <20221114232827.835599-1-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20221114232807.GA834337@paulmck-ThinkPad-P17-Gen-1> References: <20221114232807.GA834337@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" One remaining clocksource-skew issue involves extreme CPU overcommit, which can cause the clocksource watchdog measurements to be delayed by tens of seconds. This in turn means that a clock-skew criterion that is appropriate for a 500-millisecond interval will instead give lots of false positives. Therefore, check for the watchdog clocksource reporting much larger or much less than the time specified by WATCHDOG_INTERVAL. In these cases, print a pr_warn() warning and refrain from marking the clocksource under test as being unstable. Reported-by: Chris Mason Signed-off-by: Paul E. McKenney Cc: John Stultz Cc: Thomas Gleixner Cc: Stephen Boyd Cc: Feng Tang Cc: Waiman Long --- kernel/time/clocksource.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index 8058bec87acee..dcaf38c062161 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -386,7 +386,7 @@ EXPORT_SYMBOL_GPL(clocksource_verify_percpu); =20 static void clocksource_watchdog(struct timer_list *unused) { - u64 csnow, wdnow, cslast, wdlast, delta; + u64 csnow, wdnow, cslast, wdlast, delta, wdi; int next_cpu, reset_pending; int64_t wd_nsec, cs_nsec; struct clocksource *cs; @@ -440,6 +440,17 @@ static void clocksource_watchdog(struct timer_list *un= used) if (atomic_read(&watchdog_reset_pending)) continue; =20 + /* Check for bogus measurements. */ + wdi =3D jiffies_to_nsecs(WATCHDOG_INTERVAL); + if (wd_nsec < (wdi >> 2)) { + pr_warn("timekeeping watchdog on CPU%d: Watchdog clocksource '%s' advan= ced only %lld ns during %d-jiffy time interval, skipping watchdog check.\n"= , smp_processor_id(), watchdog->name, wd_nsec, WATCHDOG_INTERVAL); + continue; + } + if (wd_nsec > (wdi << 2)) { + pr_warn("timekeeping watchdog on CPU%d: Watchdog clocksource '%s' advan= ced an excessive %lld ns during %d-jiffy time interval, probable CPU overut= ilization, skipping watchdog check.\n", smp_processor_id(), watchdog->name,= wd_nsec, WATCHDOG_INTERVAL); + continue; + } + /* Check the deviation from the watchdog clocksource. */ md =3D cs->uncertainty_margin + watchdog->uncertainty_margin; if (abs(cs_nsec - wd_nsec) > md) { --=20 2.31.1.189.g2e36527f23