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 597E1C54EED for ; Mon, 30 Jan 2023 10:28:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235988AbjA3K2l (ORCPT ); Mon, 30 Jan 2023 05:28:41 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56160 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235293AbjA3K2e (ORCPT ); Mon, 30 Jan 2023 05:28:34 -0500 Received: from smtp-out2.suse.de (smtp-out2.suse.de [IPv6:2001:67c:2178:6::1d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 59F73CC26 for ; Mon, 30 Jan 2023 02:28:33 -0800 (PST) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id 0F7EE1F8C4; Mon, 30 Jan 2023 10:28:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1675074512; 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=JY/cjVpmhPzLzEYZFWZeDgrA/qfqE/q6TY2Ls/ZPklg=; b=aM5A4tbecWBcuJQTpLJHIzIRojmp5ZXjAMRSW8IErgzdW+YdKgENqfuyH1q5HgsISjCS7V IsBLYegcoqwGGeu1K9MMlSIAPWFJGC6pDa2XqRpkN0uVjZqG1BMKUfJNPjYJk+cuPKh05T UE1pZIIptfJzOpPIGtyHIKOyStOV8TQ= Received: from suse.cz (unknown [10.100.201.202]) (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 DDCB12C141; Mon, 30 Jan 2023 10:28:31 +0000 (UTC) Date: Mon, 30 Jan 2023 11:28:29 +0100 From: Petr Mladek To: Weiping Zhang Cc: akpm@linux-foundation.org, peterz@infradead.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH] hung_task: show sysctl_hung_task_warnings Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun 2023-01-29 17:08:29, Weiping Zhang wrote: > Sorry for the late reply. > > On Fri, Jan 13, 2023 at 9:43 PM Petr Mladek wrote: > > > > On Thu 2023-01-12 17:17:45, Weiping Zhang wrote: > > > This patch try to add more debug info to detect lost kernel log or no > > > hung task was detected. > > > > > > The user set 10 to the hung_task_timeout_secs, the kernel log: > > > > > > [ 3942.642220] INFO: task mount:19066 blocked for more than 10 seconds. > > > [ 3952.876768] INFO: task kworker/u81:0:7 blocked for more than 10 seconds. > > > [ 3952.877088] INFO: task scsi_eh_0:506 blocked for more than 10 seconds. > > > [ 3952.878212] INFO: task mount:19066 blocked for more than 10 seconds. > > > [ 3963.116805] INFO: task kworker/u81:0:7 blocked for more than 10 seconds. > > > [ 3963.117137] INFO: task scsi_eh_0:506 blocked for more than 10 seconds. > > > [ 3963.118275] INFO: task mount:19066 blocked for more than 10 seconds. > > > [ 3973.356837] INFO: task kworker/u81:0:7 blocked for more than 10 seconds. > > > [ 3973.357148] INFO: task scsi_eh_0:506 blocked for more than 10 seconds. > > > [ 3973.358247] INFO: task mount:19066 blocked for more than 10 seconds. > > Expect but no hung task log at this moment. > > > > [ 3993.836899] INFO: task kworker/u81:0:7 blocked for more than 10 seconds. > > > [ 3993.837238] INFO: task scsi_eh_0:506 blocked for more than 10 seconds. > > > [ 3993.838356] INFO: task mount:19066 blocked for more than 10 seconds. > > > > > > There is no any log at about 3983, it's hard to know if kernel log was > > > lost or there is no hung task was detected at that moment. So this patch > > > print sysctl_hung_task_warnings to distinguish the above two cases. > > > > > > Signed-off-by: Weiping Zhang > > > --- > > > kernel/hung_task.c | 5 ++++- > > > 1 file changed, 4 insertions(+), 1 deletion(-) > > > > > > diff --git a/kernel/hung_task.c b/kernel/hung_task.c > > > index c71889f3f3fc..ca917931473d 100644 > > > --- a/kernel/hung_task.c > > > +++ b/kernel/hung_task.c > > > @@ -127,8 +127,11 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout) > > > * complain: > > > */ > > > if (sysctl_hung_task_warnings) { > > > - if (sysctl_hung_task_warnings > 0) > > > + if (sysctl_hung_task_warnings > 0) { > > > sysctl_hung_task_warnings--; > > > + pr_err("sysctl_hung_task_warnings: %d\n", > > > + sysctl_hung_task_warnings); > > > + } > > > > It is too much noise. But it might make sense to report it when > > the counter gets down to zero. Something like: > > > > if (sysctl_hung_task_warnings) > > pr_info("Future hung task reports are suppressed, see sysctl kernel.hung_task_warnings\n"); > > > > and move this down after printing all the details for this hung task report. > I'm fine to print this warning when it gets down to 0. I prefer this variant. > The warning counter is useful to detect kernel log lost or not, if add > a new line to print this count is too noise, > how about append this counter at the end of the following line: > pr_err("INFO: task %s:%d blocked for more than %ld seconds, > sysctl_hung_task_warnings: %d\n", > t->comm, t->pid, (jiffies - t->last_switch_time) / HZ, > sysctl_hung_task_warnings); Is it really important to print this on every line, please? IMHO, most people do not care. IMHO. it would add more harm (confusion, noise) than good. Best Regards, Petr