From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-98.freemail.mail.aliyun.com (out30-98.freemail.mail.aliyun.com [115.124.30.98]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7EAAF3F411F; Fri, 26 Jun 2026 12:06:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.98 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782475604; cv=none; b=FIA11OUZpHRf/kq9rfIG5fy7xpLpL7KGMsE7UA5AMIX8B4ioGM9UF4fzaea8+k0FGfMtHIVlEhBG9hANNxZZbbpGf1lNaYIksQRWX7RQJ4/Nwspn33vUi6FeD3BNhUzZ/+SbhQPOm0A+olWBgnewB5SwzWmmxQ9+3NPwvUPzsTM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782475604; c=relaxed/simple; bh=mcnd45m9iaSfOflkxyHGds0Du5OyNPMd9m09tACMtgo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=gi8rJl5AZa1DFN91e5jsc2KKffIGTmj4l3Rxjn1cj9ZQ8WYNCY27cAoPV+vy3oymscX0+bMR5oAG9gPgCIK2AfgEMYNadaJ9tvtI6IbthK3iwScGeGsS6uzI5IVo8XjBgpq3jJnos4vl8wBfmyML3AcKPzz9Muj3f6oQS5qeBHw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=wV7Ngncp; arc=none smtp.client-ip=115.124.30.98 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="wV7Ngncp" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1782475592; h=Date:From:To:Subject:Message-ID:MIME-Version:Content-Type; bh=xh7XI+TiHLJYLAr/894grpqUh7uVtoi8+UIaxKwNZeY=; b=wV7NgncpXJrbs0BMvAsSh8tkGgRO9TUTqmSqn9LMGDt1q0ul38eEE0U0btGoxY8eqzk5Hj/d6JW4w3skh2/p2rwXrb500qbZXDLtMYyQWrVtOjNEs7X/NgU6sIr2f7nxFj89phqtQ3BNWLTFCCUeOkilFCvJLfBZ2xULSXg2P04= 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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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