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 237BBC43334 for ; Tue, 19 Jul 2022 20:45:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237475AbiGSUpF (ORCPT ); Tue, 19 Jul 2022 16:45:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57908 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238143AbiGSUpB (ORCPT ); Tue, 19 Jul 2022 16:45:01 -0400 Received: from fanzine2.igalia.com (fanzine.igalia.com [178.60.130.6]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 02D99599D4; Tue, 19 Jul 2022 13:45:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=igalia.com; s=20170329; h=Content-Transfer-Encoding:Content-Type:In-Reply-To:From: References:Cc:To:Subject:MIME-Version:Date:Message-ID:Sender:Reply-To: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=mm6gaIG3ulRS6bYmNbpjfA3sE2i3p2OSI7BJX/PQ87M=; b=NHRZ5ZOoSJvZ1rx0k+qAorgHi+ ysh3vwi0PmqkJ+sGT7WvvQq42Iam55ZtfsYvuSe8jlWS3T5GO6WFTAJPoBvG8B0awkYvog91umeP9 Uy9+z9l79ZNg4uOpd7S9OPocCVgkb02y0J3HsguQ5KVTAI49LNiEt9sPKWHn2I9cb6QoKgN6FB9Kg nC7EdVklSTsvadIYvBBICjf9v+16T5FuWpJnr1e48reVt+ocCZ9LYMX8lFiuwZHLqGO0dgF535kiv pv2Ma+2wbPCi1qg2RE2gqrjaTAHsDQjqblHKykFE7WpSED9UQK0QBFo9aHF9TjvED8BhtMx764WgT m/JB4MpQ==; Received: from 200-100-212-117.dial-up.telesp.net.br ([200.100.212.117] helo=[192.168.1.60]) by fanzine2.igalia.com with esmtpsa (Cipher TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_128_GCM:128) (Exim) id 1oDu59-006j7M-DT; Tue, 19 Jul 2022 22:44:39 +0200 Message-ID: <8e201d99-78a8-d68c-6d33-676a1ba5a6ee@igalia.com> Date: Tue, 19 Jul 2022 17:44:03 -0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.0 Subject: Re: [PATCH v2 09/13] notifier: Show function names on notifier routines if DEBUG_NOTIFIERS is set Content-Language: en-US To: Arjan van de Ven , akpm@linux-foundation.org, bhe@redhat.com, pmladek@suse.com, kexec@lists.infradead.org Cc: linux-kernel@vger.kernel.org, linux-hyperv@vger.kernel.org, netdev@vger.kernel.org, x86@kernel.org, kernel-dev@igalia.com, kernel@gpiccoli.net, halves@canonical.com, fabiomirmar@gmail.com, alejandro.j.jimenez@oracle.com, andriy.shevchenko@linux.intel.com, arnd@arndb.de, bp@alien8.de, corbet@lwn.net, d.hatayama@jp.fujitsu.com, dave.hansen@linux.intel.com, dyoung@redhat.com, feng.tang@intel.com, gregkh@linuxfoundation.org, mikelley@microsoft.com, hidehiro.kawai.ez@hitachi.com, jgross@suse.com, john.ogness@linutronix.de, keescook@chromium.org, luto@kernel.org, mhiramat@kernel.org, mingo@redhat.com, paulmck@kernel.org, peterz@infradead.org, rostedt@goodmis.org, senozhatsky@chromium.org, stern@rowland.harvard.edu, tglx@linutronix.de, vgoyal@redhat.com, vkuznets@redhat.com, will@kernel.org, Cong Wang , Sebastian Andrzej Siewior , Valentin Schneider , Xiaoming Ni References: <20220719195325.402745-1-gpiccoli@igalia.com> <20220719195325.402745-10-gpiccoli@igalia.com> From: "Guilherme G. Piccoli" In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19/07/2022 17:33, Arjan van de Ven wrote: > On 7/19/2022 12:53 PM, Guilherme G. Piccoli wrote: >> Currently we have a debug infrastructure in the notifiers file, but >> it's very simple/limited. Extend it by: >> >> (a) Showing all registered/unregistered notifiers' callback names; > > > I'm not yet convinced that this is the right direction. > The original intent for this "debug" feature was to be lightweight enough that it could run in production, since at the time, rootkits > liked to clobber/hijack notifiers and there were also some other signs of corruption at the time. > > By making something print (even at pr_info) for what are probably frequent non-error operations, you turn something that is light > into something that's a lot more heavy and generally that's not a great idea... it'll be a performance surprise. > > Is registering/un-registering notifiers a hot path, or performance sensitive usually? For me, this patch proved to be very useful, and once enabled, shows relatively few entries in dmesg, these operations aren't so common thing it seems. Also, if this Kconfig option was meant to run in production, maybe the first thing would be have some sysfs tuning or anything able to turn it on - I've worked with a variety of customers and the most terrifying thing in servers is to install a new kernel and reboot heh My understanding is that this debug infrastructure would be useful for notifiers writers and people playing with the core notifiers code...tracing would be much more useful in the context of checking if some specific notifier got registered/executed in production environment I guess. Cheers, Guilherme 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 4305CC43334 for ; Wed, 20 Jul 2022 06:03:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:From:References:Cc:To: Subject:MIME-Version:Date:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=XVaIw1LEBWx9N163sfmYVakgvGqjy3P576C5M9qryVU=; b=g/XO9n83Piux4K NXlvqTJ5EaC+2c+K9/p7TbyY4EoKgamIQVy5lvi0xTmEARpCFppsOHSayx8IpnsGxx4j79Cm+0Qo5 WbH2KT10YPAW0DXhKrTfcTxpGOBBbn2DMiCLv6xXQiplE+AbWjTMbm7uxkShjgKOAAjFrP8OxUdW3 VE1/xgXcOKfp2sGOu+8ykJxSi5knPym7oO7CwZgBCgmlO0vVKqLE5lndPc8CBlwVNd3nMkL5RL5fy EeLNnsuDVQupAwiDLYgfTJ1RhoIlzVjqQrFdZwNH5So6bByGFNi7xztkgd8M5sgXYP1iC9oaKojGm O1CPoLRTQ5kXJZgrZrsg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1oE2o4-000syH-IT; Wed, 20 Jul 2022 06:03:36 +0000 Received: from fanzine.igalia.com ([178.60.130.6] helo=fanzine2.igalia.com) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1oDu5Q-00CpTb-A8 for kexec@lists.infradead.org; Tue, 19 Jul 2022 20:44:58 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=igalia.com; s=20170329; h=Content-Transfer-Encoding:Content-Type:In-Reply-To:From: References:Cc:To:Subject:MIME-Version:Date:Message-ID:Sender:Reply-To: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=mm6gaIG3ulRS6bYmNbpjfA3sE2i3p2OSI7BJX/PQ87M=; b=NHRZ5ZOoSJvZ1rx0k+qAorgHi+ ysh3vwi0PmqkJ+sGT7WvvQq42Iam55ZtfsYvuSe8jlWS3T5GO6WFTAJPoBvG8B0awkYvog91umeP9 Uy9+z9l79ZNg4uOpd7S9OPocCVgkb02y0J3HsguQ5KVTAI49LNiEt9sPKWHn2I9cb6QoKgN6FB9Kg nC7EdVklSTsvadIYvBBICjf9v+16T5FuWpJnr1e48reVt+ocCZ9LYMX8lFiuwZHLqGO0dgF535kiv pv2Ma+2wbPCi1qg2RE2gqrjaTAHsDQjqblHKykFE7WpSED9UQK0QBFo9aHF9TjvED8BhtMx764WgT m/JB4MpQ==; Received: from 200-100-212-117.dial-up.telesp.net.br ([200.100.212.117] helo=[192.168.1.60]) by fanzine2.igalia.com with esmtpsa (Cipher TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_128_GCM:128) (Exim) id 1oDu59-006j7M-DT; Tue, 19 Jul 2022 22:44:39 +0200 Message-ID: <8e201d99-78a8-d68c-6d33-676a1ba5a6ee@igalia.com> Date: Tue, 19 Jul 2022 17:44:03 -0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.0 Subject: Re: [PATCH v2 09/13] notifier: Show function names on notifier routines if DEBUG_NOTIFIERS is set Content-Language: en-US To: Arjan van de Ven , akpm@linux-foundation.org, bhe@redhat.com, pmladek@suse.com, kexec@lists.infradead.org Cc: linux-kernel@vger.kernel.org, linux-hyperv@vger.kernel.org, netdev@vger.kernel.org, x86@kernel.org, kernel-dev@igalia.com, kernel@gpiccoli.net, halves@canonical.com, fabiomirmar@gmail.com, alejandro.j.jimenez@oracle.com, andriy.shevchenko@linux.intel.com, arnd@arndb.de, bp@alien8.de, corbet@lwn.net, d.hatayama@jp.fujitsu.com, dave.hansen@linux.intel.com, dyoung@redhat.com, feng.tang@intel.com, gregkh@linuxfoundation.org, mikelley@microsoft.com, hidehiro.kawai.ez@hitachi.com, jgross@suse.com, john.ogness@linutronix.de, keescook@chromium.org, luto@kernel.org, mhiramat@kernel.org, mingo@redhat.com, paulmck@kernel.org, peterz@infradead.org, rostedt@goodmis.org, senozhatsky@chromium.org, stern@rowland.harvard.edu, tglx@linutronix.de, vgoyal@redhat.com, vkuznets@redhat.com, will@kernel.org, Cong Wang , Sebastian Andrzej Siewior , Valentin Schneider , Xiaoming Ni References: <20220719195325.402745-1-gpiccoli@igalia.com> <20220719195325.402745-10-gpiccoli@igalia.com> From: "Guilherme G. Piccoli" In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220719_134456_712769_736C3977 X-CRM114-Status: GOOD ( 15.89 ) X-Mailman-Approved-At: Tue, 19 Jul 2022 23:02:40 -0700 X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+kexec=archiver.kernel.org@lists.infradead.org On 19/07/2022 17:33, Arjan van de Ven wrote: > On 7/19/2022 12:53 PM, Guilherme G. Piccoli wrote: >> Currently we have a debug infrastructure in the notifiers file, but >> it's very simple/limited. Extend it by: >> >> (a) Showing all registered/unregistered notifiers' callback names; > > > I'm not yet convinced that this is the right direction. > The original intent for this "debug" feature was to be lightweight enough that it could run in production, since at the time, rootkits > liked to clobber/hijack notifiers and there were also some other signs of corruption at the time. > > By making something print (even at pr_info) for what are probably frequent non-error operations, you turn something that is light > into something that's a lot more heavy and generally that's not a great idea... it'll be a performance surprise. > > Is registering/un-registering notifiers a hot path, or performance sensitive usually? For me, this patch proved to be very useful, and once enabled, shows relatively few entries in dmesg, these operations aren't so common thing it seems. Also, if this Kconfig option was meant to run in production, maybe the first thing would be have some sysfs tuning or anything able to turn it on - I've worked with a variety of customers and the most terrifying thing in servers is to install a new kernel and reboot heh My understanding is that this debug infrastructure would be useful for notifiers writers and people playing with the core notifiers code...tracing would be much more useful in the context of checking if some specific notifier got registered/executed in production environment I guess. Cheers, Guilherme _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec