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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3AA5FCD4F26 for ; Fri, 26 Jun 2026 12:06:44 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [127.0.0.1]) by lists.ozlabs.org (Postfix) with ESMTP id 4gmvXy3qfHz2yYd; Fri, 26 Jun 2026 22:06:42 +1000 (AEST) Authentication-Results: lists.ozlabs.org; arc=none smtp.remote-ip=115.124.30.110 ARC-Seal: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1782475602; cv=none; b=kPF27FbZ2j1JKlzux7dzJFexiLpMeZls1CSFnj8/OR1vTiNXBIJ8zbVAOC4BiwolhUkApMgXme/FS5dhmLp8Sj1IGveGwilqMSyw189QAHJdRHjTNBldJEEcTlqi37WdcPtPpEwL4UMgzvnpCGSGlC6CdgehewM95aK/gc3z+D76k9bMyvogLqZEsGqXkPHNOJ+FaaoP6iYzI283xLFc+9lDaK+nKUW53oz8XEQo79oH9nkuV2zb2S4B20xpeBds7qpoZgEx7cTJ02PJrfnug4oSAlF4lPbsxueLtIQlm70+qqo2Evn8vIAOtChKmj0q0mu8gI/xzq+8GcavWNJx/Q== ARC-Message-Signature: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1782475602; c=relaxed/relaxed; bh=xh7XI+TiHLJYLAr/894grpqUh7uVtoi8+UIaxKwNZeY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=UiOTvT+mHWOzoREY/56eFMb+affq5PQOqI60QADW7QLWZxtDY0dn3srSJ+z6V5wUeMDkXMeBdy9NnlidfD9Bu2iJZWu2P7dl7ZynptvSXPsNvJfaS722EWLXKdtNG1KbeL6PDixduL/V5rV0bvROdd5g3oeHv8qYiXVopK2o/MOXS5Z+r3irdbAiVOrUkBlpAgaAGOZFej7r5qajn479YXF/sEfpz6zNcg09gZwWMKvlIDoKo1XnR9defUXYKtdBrPx7eGVxGcfOKwHBeopGZQ4nrcKD/b8VLH0lnMmnhWlcEd6Ck4uIldD7qr/bEU6tow3q8QmuBSSIjH34yswY5w== ARC-Authentication-Results: i=1; lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; dkim=pass (1024-bit key; unprotected) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.a=rsa-sha256 header.s=default header.b=kgTg34on; dkim-atps=neutral; spf=pass (client-ip=115.124.30.110; helo=out30-110.freemail.mail.aliyun.com; envelope-from=feng.tang@linux.alibaba.com; receiver=lists.ozlabs.org) smtp.mailfrom=linux.alibaba.com Authentication-Results: lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: lists.ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.a=rsa-sha256 header.s=default header.b=kgTg34on; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=linux.alibaba.com (client-ip=115.124.30.110; helo=out30-110.freemail.mail.aliyun.com; envelope-from=feng.tang@linux.alibaba.com; receiver=lists.ozlabs.org) Received: from out30-110.freemail.mail.aliyun.com (out30-110.freemail.mail.aliyun.com [115.124.30.110]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange x25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4gmvXw0rjxz2xn3 for ; Fri, 26 Jun 2026 22:06:38 +1000 (AEST) DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1782475593; h=Date:From:To:Subject:Message-ID:MIME-Version:Content-Type; bh=xh7XI+TiHLJYLAr/894grpqUh7uVtoi8+UIaxKwNZeY=; b=kgTg34on1n4/iVtW/7HMWkSoZ1RyYc4+KWeX7kX7Pn1ktLDVUPQOSUUPJ6F3MyB5AhZ+Wt7ZJlpSSfgwi4rop0t/Kn9jXVHyzvfkS21O3VEyDU1AMiTfyAKaE9YiKJBkVqwEUycoLMTSVoMkYdnF4wcUqFsIuXl9ieHGfM/uegg= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R161e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033037009110;MF=feng.tang@linux.alibaba.com;NM=1;PH=DS;RN=12;SR=0;TI=SMTPD_---0X5et9EI_1782475590; Received: from localhost(mailfrom:feng.tang@linux.alibaba.com fp:SMTPD_---0X5et9EI_1782475590 cluster:ay36) by smtp.aliyun-inc.com; Fri, 26 Jun 2026 20:06:31 +0800 Date: Fri, 26 Jun 2026 20:06:29 +0800 From: Feng Tang To: Petr Mladek Cc: Bradley Morgan , Andrew Morton , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Madhavan Srinivasan , Douglas Anderson , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, stable@vger.kernel.org Subject: Re: [PATCH v3 4/4] panic: use sys_info_with_filter() to avoid duplicate backtraces Message-ID: References: <20260625152558.7450-1-include@grrlz.net> <20260625152558.7450-5-include@grrlz.net> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: On Fri, Jun 26, 2026 at 12:23:48PM +0200, Petr Mladek wrote: > On Thu 2026-06-25 15:25:58, Bradley Morgan wrote: > > panic_other_cpus_shutdown() handles SYS_INFO_ALL_BT before stopping the > > other CPUs. Do not ask sys_info() to handle that bit again later in the > > panic path. > > > > Use sys_info_with_filter() so panic_print=all_bt does not request more > > output after the CPUs are stopped. > > > > Fixes: a9af76a78760 ("watchdog: add sys_info sysctls to dump sys info on system lockup") > > Cc: stable@vger.kernel.org > > Signed-off-by: Bradley Morgan > > --- > > kernel/panic.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/kernel/panic.c b/kernel/panic.c > > index 213725b612aa..eb842823df61 100644 > > --- a/kernel/panic.c > > +++ b/kernel/panic.c > > @@ -680,7 +680,7 @@ void vpanic(const char *fmt, va_list args) > > */ > > atomic_notifier_call_chain(&panic_notifier_list, 0, buf); > > > > - sys_info(panic_print); > > + sys_info_with_filter(panic_print, SYS_INFO_ALL_BT); > > Hmm, this prevents printing backtraces from all CPUs completely. > But what if they were not printed? > > They might be printed by: > > static void panic_other_cpus_shutdown(bool crash_kexec) > { > if (panic_print & SYS_INFO_ALL_BT) > panic_trigger_all_cpu_backtrace(); > > [...] > } > > But it checks only "panic_print" variable. It won't do anything > when (panic_print == 0). > > In this case, we might still want to print the backraces when > SYS_INFO_ALL_BT is set in kernel_si_info. Yep. > > > kmsg_dump_desc(KMSG_DUMP_PANIC, buf); > > Of course, we might fix panic_other_cpus_shutdown() to check also > kernel_si_info. > > But it all becomes very hairy. We have several levels: > > + watchdog-all_bt-specific option, e.g. sysctl_hardlockup_all_cpu_backtrace > > + watchdog-specific si_info preferences, e.g. hardlockup_si_mask > > + panic-specific si_info: panic_print > > + universal fallback for any layer: kernel_si_info > > Now, we try to check all these variables back and forth to > trigger all backtraces or to avoid triggering them. > And it clearly does not work well and the code is more and more > hairy. Agree :) > I think about another approach. The word "waterfall" comes to my mind. > Instead of checking all the settings back and forth, let's process > each setting one by one and just remember what has been done and > skip this in the next level. When initially reviewing V2's 4th patch, I thought about the 'panic_this_cpu_backtrace_printed', but it's a local variable which records the state. > All the si_info actions seems to dump a global system state. > So, it would make sense to remember the state in a global variable > even when it might be modified by more CPUs in parallel. IIUC, panic case is kind of special, as it has to separate the 'sys_info()' op in different stage. Can we do a merge in the start of vpanic() by: panic_print = panic_print ?: kernel_si_mask; as a addon patch ? Thanks, Feng > I am going to think more about it. > > Please, do not send v4 until the discussion settles! > > Best Regards, > Petr