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 X-Spam-Level: X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B9FABC433E0 for ; Wed, 24 Mar 2021 08:42:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8D2D6619F8 for ; Wed, 24 Mar 2021 08:42:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234106AbhCXIlg (ORCPT ); Wed, 24 Mar 2021 04:41:36 -0400 Received: from mx2.suse.de ([195.135.220.15]:41698 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231453AbhCXIlP (ORCPT ); Wed, 24 Mar 2021 04:41:15 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1616575274; 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=PxMDSdG3FPE34dQL3+yxqk6XbvrySDv1MamsG1KJkTk=; b=vKGWrrSvKplvLhXHHXnAhJQQ7GcmXbAEIDlUMOcwilomqaipLvDDLPYaekyjsWJqsWBF7S qLohTm/02Rb9f2zhovhmyAouZCmBLTROMTnmQJli478T/JdkuNL2TFvFIeuFPAJY5t/lW1 YBv27T7nzY9V7Cmma1PM53JqkGiem2A= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 57117AB9B; Wed, 24 Mar 2021 08:41:14 +0000 (UTC) Date: Wed, 24 Mar 2021 09:41:13 +0100 From: Petr Mladek To: John Ogness Cc: Sergey Senozhatsky , Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: Re: [PATCH next v1 1/3] printk: track/limit recursion Message-ID: References: <20210316233326.10778-1-john.ogness@linutronix.de> <20210316233326.10778-2-john.ogness@linutronix.de> <87czvp7e0f.fsf@jogness.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87czvp7e0f.fsf@jogness.linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 2021-03-23 22:32:00, John Ogness wrote: > On 2021-03-22, Petr Mladek wrote: > > On Wed 2021-03-17 00:33:24, John Ogness wrote: > >> Track printk() recursion and limit it to 3 levels per-CPU and per-context. > > > >> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c > >> index 2f829fbf0a13..c666e3e43f0c 100644 > >> --- a/kernel/printk/printk.c > >> +++ b/kernel/printk/printk.c > >> +/* Return a pointer to the dedicated counter for the CPU+context of the caller. */ > >> +static char *printk_recursion_counter(void) > >> +{ > >> + int ctx = 0; > >> + > >> +#ifdef CONFIG_PRINTK_NMI > >> + if (in_nmi()) > >> + ctx = 1; > >> +#endif > >> + if (!printk_percpu_data_ready()) > >> + return &printk_count_early[ctx]; > >> + return &((*this_cpu_ptr(&printk_count))[ctx]); > >> +} > > > > It is not a big deal. But using an array for two contexts looks strange > > especially when only one is used on some architectures. > > Also &((*this_cpu_ptr(&printk_count))[ctx]) is quite tricky ;-) > > > > What do you think about the following, please? > > > > static DEFINE_PER_CPU(u8 printk_count); > > static u8 printk_count_early; > > > > #ifdef CONFIG_HAVE_NMI > > static DEFINE_PER_CPU(u8 printk_count_nmi); > > static u8 printk_count_nmi_early; > > #endif > > > > static u8 *printk_recursion_counter(void) > > { > > if (IS_ENABLED(CONFIG_HAVE_NMI) && in_nmi()) { > > if (printk_cpu_data_ready()) > > return this_cpu_ptr(&printk_count_nmi); > > return printk_count_nmi_early; > > } > > > > if (printk_cpu_data_ready()) > > return this_cpu_ptr(&printk_count); > > return printk_count_early; > > } > > I can split it into explicit variables. But is the use of the IS_ENABLED > macro preferred over ifdef? I would prefer: > > static u8 *printk_recursion_counter(void) > { > #ifdef CONFIG_HAVE_NMI > if (in_nmi()) { > if (printk_cpu_data_ready()) > return this_cpu_ptr(&printk_count_nmi); > return printk_count_nmi_early; > } > #endif > if (printk_cpu_data_ready()) > return this_cpu_ptr(&printk_count); > return printk_count_early; > } > > Since @printk_count_nmi and @printk_count_nmi_early would not exist, I > would prefer the pre-processor removes that code block rather than > relying on compiler optimization. Feel free to use #ifdef. Best Regards, Petr