From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-186.mta1.migadu.com (out-186.mta1.migadu.com [95.215.58.186]) (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 717D52A1AA for ; Fri, 16 May 2025 13:39:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.186 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747402784; cv=none; b=rHuMhiX/HJl7LPrj5ihLiJXK8f0mVBxb9dQBhwgY9cL9qfwQbRgskqJ7vyTuSIvgqcjvzigyi2J8bY4LSSw6WFYQIM0WW266gSFPaJPtAldy5rTBjHsSqJPNEzQY54aT/3e71bQZIb4YdXeFe9B2j7TbSoQSbKOcbs3WcG0QkCk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747402784; c=relaxed/simple; bh=79PCKBKRp0CwDGfFCJ74eyyNnbgDY/+feymcdxAD/VE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=AVJslqmI1he3Nzag+XXBQyjJn+qmbkcNuGplAeV7eDJq30AdZ4FD8MWhnN5XopvbPM3SAVHj1JDxI6ipe0HmyEAMzgdf5L3GNLjzGEGNZx+KUFcw1Tnv++WKRUoW5CZegiWIQE8r0FsrxCBKmOTAHArdsafC0M4tGAj40q+chFQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=WIBIYOOs; arc=none smtp.client-ip=95.215.58.186 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="WIBIYOOs" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1747402779; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=FCq2w8JhXMnNVPlpwQulrw1FJv4lSu5R3EjdeUnPnHw=; b=WIBIYOOstK3VQOZonAw8xyYyrHZUDkON3jO56h3s7N8e8GRVl8RJGfTcl/iJ0Go0AN8g+0 l6e+tlXgPHrU7ad0UCIVGo6smX/kvYTEOn+k33XUgHLGyu1/sMT4OAsNAaNDWGFwO8+1gH VDQ46ETgfxVih/sGEFhDjEL+b2DFXGg= Date: Fri, 16 May 2025 21:39:23 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v1 1/3] kernel/panic: generalize panic_print's function to show sys info Content-Language: en-US To: Feng Tang , Petr Mladek Cc: Andrew Morton , Steven Rostedt , linux-kernel@vger.kernel.org, mhiramat@kernel.org, llong@redhat.com, "Paul E. McKenney" References: <20250511085254.61446-1-feng.tang@linux.alibaba.com> <20250511085254.61446-2-feng.tang@linux.alibaba.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 2025/5/16 13:38, Feng Tang wrote: > On Thu, May 15, 2025 at 12:32:04PM +0200, Petr Mladek wrote: >> On Tue 2025-05-13 21:23:25, Feng Tang wrote: >>> Hi Petr, >>> >>> Thanks for the review! >>> >>> On Tue, May 13, 2025 at 11:57:19AM +0200, Petr Mladek wrote: >>>> On Sun 2025-05-11 16:52:52, Feng Tang wrote: >>>>> panic_print was introduced to help debugging kernel panic by dumping >>>>> different kinds of system information like tasks' call stack, memory, >>>>> ftrace buffer etc. Acutually this function could help debugging cases >>>>> like task-hung, soft/hard lockup too, where user may need the snapshot >>>>> of system info at that time. >>>>> >>>> The generic approach might deserve a separate source file, >>>> for example: >>>> >>>> include/linux/sys_info.h >>>> lib/sys_info.c >>> >>> Thanks for the suggestion! I'm really not good at naming. >>> >>> As panic.c is always built-in, I'll put sys_info.c as obj-y. >> >> Makes sense. >> >>>> Also I always considered the bitmask as a horrible user interface. >>>> It might be used internally. But it would be better to allow a human >>>> readable parameter, for example: >>>> >>>> panic_sys_info=task,mem,timer,lock,ftrace,bt,all_bt,blocked_tasks >>> >>> Yes, it's convenient for developers, as a cmdline parameter being parsed >>> at boot time. >>> >>> But I think bitmask may be easier for runtime changing as a core parameter >>> under /proc/ or /sys/, or from sysctl interface. There are also some other >>> modules use debug bitmask controlling printking info for different >>> sub-components. >> >> Good to know. Could you please give me a pointer to some other modules >> using the bitmask? I believe that they exist but I can't find any. >> I wonder how common it is... > > Definitely not common :) I only know one: ACPI, which has 2 debug knobs, > 'debug_layer' is a bigmap to control which sub-component's msg to be > dumped, and 'debug_level'. > >> Anyway, I personally find words/names easier to use. > > True. For me, I have some notes sticked on my monitor: one about characters > for /proc/sysrq-trigger, one for panic_print, one for struct page's flag :) > >> For example, >> I like the following interfaces: >> >> #> cat /sys/power/pm_test >> [none] core processors platform devices freezer >> >> #> cat /sys/kernel/debug/tracing/available_tracers >> blk function_graph wakeup_dl wakeup_rt wakeup function nop >> >> #> cat /proc/sys/kernel/seccomp/actions_avail >> kill_process kill_thread trap errno user_notif trace log allow >> # cat /proc/sys/kernel/seccomp/actions_logged >> kill_process kill_thread trap errno user_notif trace log > > Thanks for the info, will check them. > >>> And we have similar control knobs for hung, lockup etc. >>> >>> Or should I change the name from 'xxx_print_mask' to 'xxx_sysinfo_flag' >>> in patch 2/3 ? >>> >>>> >>>> The console reply might be handled by a separate: >>>> >>>> panic_console_reply=1 >>>> >>>> And it would obsolete the existing "panic_print" which is an >>>> ugly name and interface from my POV. >>> >>> Agree it's ugly :). But besides a kernel parameter, 'panic_print' is >>> also a sysctl interface, I'm afraid renaming it might break user ABI. >> >> A solution would be to keep it and create "panic_sys_info=" >> with the human readable parameters in parallel. They would >> store the request in the same bitmap. >> >> We could print a message that "panic_print" has been obsoleted >> by "panic_sys_info" when people use it. >> >> Both parameters would override the current bitmap. So the later >> used parameter or procfs/sysfs write would win. > > Reasonalbe. > >> Note: >> >> One question is whether to use sysctl or module parameters. >> >> An advantage of sysctl is the "systcl" userspace tool. Some people >> might like it. But the API is very old and a bit cumbersome for >> implementing. >> >> The sysfs, aka include/linux/moduleparam.h, API looks cleaner to me. >> But the parameters are hidden in the /sys/... jungle ;-) >> >> I would slightly prefer "sysctl" because these parameters are easier >> to find. > > I will think about the string parsing in sys_info.c, and in the backend, > a bitmap is still needed to save the parsing result, and as the parameter > for sys_show_info(). > > Also if we go 'sysctl' way, in the future, some exising interface like > 'sysctl_hung_task_all_cpu_backtrace' could be deprecated and integrated > into the 'hung_task_sys_info'? Works for me. Let's go with 'sysctl' approach, and 'hung_task_all_cpu_backtrace' could be deprecated, though it won't be removed anytime soon. IMHO, 'hung_task_sys_info' is more organized and easier to expand - plus these parameters are much easier to find as Petr said ;) Thanks, Lance > > Thanks, > Feng > >> Best Regards, >> Petr