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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, 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 17B01C433E5 for ; Mon, 22 Mar 2021 14:52:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C40836198E for ; Mon, 22 Mar 2021 14:51:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230527AbhCVOvt (ORCPT ); Mon, 22 Mar 2021 10:51:49 -0400 Received: from mx2.suse.de ([195.135.220.15]:49868 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230140AbhCVOti (ORCPT ); Mon, 22 Mar 2021 10:49:38 -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=1616424576; 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=3DbpKA9OBqO3XfNQwyv7fij4KDSvOgOatNqN0b+8D2c=; b=Yj7L9okmiPiykV9gepg/YwHFiQBflhdBjAdWcshdxGrsE9gOabJ/wSuLLLUQbrMjdyoXc9 zrlp9eCXwWiGSLUjtNN8kzjEogYFBwcz093bHrtf0OMgvMtn8SeLDq1GLjte9QMYTiZqHc alVSDXlO8/gojufz/K0Q0DA3LNFghSA= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id E8655AC1F; Mon, 22 Mar 2021 14:49:35 +0000 (UTC) Date: Mon, 22 Mar 2021 15:49:35 +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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210316233326.10778-2-john.ogness@linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Please, explain why it is added. I mean that it will allow remove printk_safe that provides recursion protection at the moment. > Signed-off-by: John Ogness > --- > kernel/printk/printk.c | 80 ++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 77 insertions(+), 3 deletions(-) > > 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 > @@ -1940,6 +1940,71 @@ static void call_console_drivers(const char *ext_text, size_t ext_len, > } > } > > +/* > + * Recursion is tracked separately on each CPU. If NMIs are supported, an > + * additional NMI context per CPU is also separately tracked. Until per-CPU > + * is available, a separate "early tracking" is performed. > + */ > +#ifdef CONFIG_PRINTK_NMI CONFIG_PRINTK_NMI is a shortcut for CONFIG_PRINTK && CONFIG_HAVE_NMI. It should be possible to use CONFIG_HAVE_NMI here because this should be in section where CONFIG_PRINTK is defined. This would make sense if it allows to remove CONFIG_PRINTK_NMI entirely. IMHO, it would be nice to remove one layer in the config options of possible. > +#define PRINTK_CTX_NUM 2 > +#else > +#define PRINTK_CTX_NUM 1 > +#endif > +static DEFINE_PER_CPU(char [PRINTK_CTX_NUM], printk_count); > +static char printk_count_early[PRINTK_CTX_NUM]; > + > +/* > + * Recursion is limited to keep the output sane. printk() should not require > + * more than 1 level of recursion (allowing, for example, printk() to trigger > + * a WARN), but a higher value is used in case some printk-internal errors > + * exist, such as the ringbuffer validation checks failing. > + */ > +#define PRINTK_MAX_RECURSION 3 > + > +/* 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; } Otherwise, it looks good to me. I like the simplicity. Best Regards, Petr