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 1907AC433EF for ; Fri, 25 Feb 2022 15:20:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241522AbiBYPUy (ORCPT ); Fri, 25 Feb 2022 10:20:54 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60480 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233524AbiBYPUv (ORCPT ); Fri, 25 Feb 2022 10:20:51 -0500 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E5EEC8C7DF; Fri, 25 Feb 2022 07:20:17 -0800 (PST) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id 20E541F380; Fri, 25 Feb 2022 15:20:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1645802416; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=76D+b8ZUFKHayJqezaXTrIOKH/+w6Mr9BDaG1qJPaqM=; b=uiwU9753hHXtDfEByGOp/4k3/mpSpC2iPS5R74LN2olK1KIV4kIuD6y8ARyLKPI+57XebW laXnAzMwXNXHJgSFsi5gA5ifwF1cCKT2ypgNk9DHv/UzKegXnyQUGwO9FQLe7NALffYOqs LFAeojvzfBLhLsnUVHoCuDy01kc+AaU= Received: from suse.cz (unknown [10.100.216.66]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 81174A3B83; Fri, 25 Feb 2022 15:20:15 +0000 (UTC) Date: Fri, 25 Feb 2022 16:20:15 +0100 From: Petr Mladek To: Lecopzer Chen Cc: linux-kernel@vger.kernel.org, Catalin Marinas , Will Deacon , Mark Rutland , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Alexander Shishkin , Jiri Olsa , Namhyung Kim , davem@davemloft.net, Matthias Brugger , Marc Zyngier , Julien Thierry , Kees Cook , Masahiro Yamada , Andrew Morton , Wang Qing , Luis Chamberlain , Xiaoming Ni , linux-arm-kernel@lists.infradead.org, linux-perf-users@vger.kernel.org, sparclinux@vger.kernel.org, linux-mediatek@lists.infradead.org, sumit.garg@linaro.org, kernelfans@gmail.com, yj.chiang@mediatek.com Subject: Re: [PATCH 4/5] kernel/watchdog: Adapt the watchdog_hld interface for async model Message-ID: References: <20220212104349.14266-1-lecopzer.chen@mediatek.com> <20220212104349.14266-5-lecopzer.chen@mediatek.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220212104349.14266-5-lecopzer.chen@mediatek.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat 2022-02-12 18:43:48, Lecopzer Chen wrote: > From: Pingfan Liu > > from: Pingfan Liu > > When lockup_detector_init()->watchdog_nmi_probe(), PMU may be not ready > yet. E.g. on arm64, PMU is not ready until > device_initcall(armv8_pmu_driver_init). And it is deeply integrated > with the driver model and cpuhp. Hence it is hard to push this > initialization before smp_init(). > > But it is easy to take an opposite approach by enabling watchdog_hld to > get the capability of PMU async. > > The async model is achieved by expanding watchdog_nmi_probe() with > -EBUSY, and a re-initializing work_struct which waits on a wait_queue_head. > > Signed-off-by: Pingfan Liu > Co-developed-by: Lecopzer Chen > Signed-off-by: Lecopzer Chen > --- > kernel/watchdog.c | 56 +++++++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 54 insertions(+), 2 deletions(-) > > diff --git a/kernel/watchdog.c b/kernel/watchdog.c > index b71d434cf648..fa8490cfeef8 100644 > --- a/kernel/watchdog.c > +++ b/kernel/watchdog.c > @@ -839,16 +843,64 @@ static void __init watchdog_sysctl_init(void) > #define watchdog_sysctl_init() do { } while (0) > #endif /* CONFIG_SYSCTL */ > > +static void lockup_detector_delay_init(struct work_struct *work); > +enum hld_detector_state detector_delay_init_state __initdata; I would call this "lockup_detector_init_state" to use the same naming scheme everywhere. > + > +struct wait_queue_head hld_detector_wait __initdata = > + __WAIT_QUEUE_HEAD_INITIALIZER(hld_detector_wait); > + > +static struct work_struct detector_work __initdata = I would call this "lockup_detector_work" to use the same naming scheme everywhere. > + __WORK_INITIALIZER(detector_work, lockup_detector_delay_init); > + > +static void __init lockup_detector_delay_init(struct work_struct *work) > +{ > + int ret; > + > + wait_event(hld_detector_wait, > + detector_delay_init_state == DELAY_INIT_READY); DELAY_INIT_READY is defined in the 5th patch. There are many other build errors because this patch uses something that is defined in the 5th patch. > + ret = watchdog_nmi_probe(); > + if (!ret) { > + nmi_watchdog_available = true; > + lockup_detector_setup(); > + } else { > + WARN_ON(ret == -EBUSY); Why WARN_ON(), please? Note that it might cause panic() when "panic_on_warn" command line parameter is used. Also the backtrace will not help much. The context is well known. This code is called from a workqueue worker. > + pr_info("Perf NMI watchdog permanently disabled\n"); > + } > +} > + > +/* Ensure the check is called after the initialization of PMU driver */ > +static int __init lockup_detector_check(void) > +{ > + if (detector_delay_init_state < DELAY_INIT_WAIT) > + return 0; > + > + if (WARN_ON(detector_delay_init_state == DELAY_INIT_WAIT)) { Again. Is WARN_ON() needed? Also the condition looks wrong. IMHO, this is the expected state. > + detector_delay_init_state = DELAY_INIT_READY; > + wake_up(&hld_detector_wait); > + } > + flush_work(&detector_work); > + return 0; > +} > +late_initcall_sync(lockup_detector_check); Otherwise, it make sense. Best Regards, Petr PS: I am not going to review the last patch because I am no familiar with arm. I reviewed just the changes in the generic watchdog code.