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=-10.2 required=3.0 tests=BAYES_00, BUG6152_INVALID_DATE_TZ_ABSURD,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,INVALID_DATE_TZ_ABSURD, 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 CFE43C433E0 for ; Mon, 1 Feb 2021 08:25:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 638F564E24 for ; Mon, 1 Feb 2021 08:25:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232500AbhBAIZS (ORCPT ); Mon, 1 Feb 2021 03:25:18 -0500 Received: from Galois.linutronix.de ([193.142.43.55]:55900 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231992AbhBAIZP (ORCPT ); Mon, 1 Feb 2021 03:25:15 -0500 From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1612167851; 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: in-reply-to:in-reply-to:references:references; bh=COXE+rKjUjFVdCCC90mnueNtt7dlhZD1higgsGocpKQ=; b=rWlEkWDzFlmlUINes8dXNgL4qJLRE+4vNJLrEwWgtwQekwh2ggA/DRGfcwoBt6+Cf66ZjM Ag5hzla1KUOsMFBkhQtsPMAw9jd+0EiqA/AvXsjLlfTNmadi+ejE30SMKxxUil/qHdpYLT Ai+bM0uy9c7S5FUu+p6rI6mvlfXa4ePBENwhhrlTpZLF50BKBjpD1dFqQhFPzdJxj4M0LP xCSH2YvMWQ+GW5XljIgukKvKlXhgb74fMMWNhJbym+eFoCvvfCckVLMbg4VNEE9iOL3Zn7 ZnnukGnBnG/ZoYjpUXSbNMkRhdajdgc9YtdGGzpILNfmYsiuLpwBa+n6YYr4iQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1612167851; 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: in-reply-to:in-reply-to:references:references; bh=COXE+rKjUjFVdCCC90mnueNtt7dlhZD1higgsGocpKQ=; b=94uRLnBHoPOM+puQUELDgZvcNxSlHJZrygNxt1rs4ckbt25Z9BUHab8M9ab/B0hZYfW2U7 7VJhU0o6LBJYoPCA== To: Petr Mladek Cc: Sergey Senozhatsky , Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: Re: LINE_MAX: was: Re: [PATCH printk-rework 04/12] printk: define CONSOLE_LOG_MAX in printk.h In-Reply-To: References: <20210126211551.26536-1-john.ogness@linutronix.de> <20210126211551.26536-5-john.ogness@linutronix.de> Date: Mon, 01 Feb 2021 09:30:10 +0106 Message-ID: <87r1m02o2d.fsf@jogness.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021-01-29, Petr Mladek wrote: >> diff --git a/include/linux/printk.h b/include/linux/printk.h >> index fe7eb2351610..6d8f844bfdff 100644 >> --- a/include/linux/printk.h >> +++ b/include/linux/printk.h >> @@ -45,6 +45,7 @@ static inline const char *printk_skip_headers(const char *buffer) >> } >> >> #define CONSOLE_EXT_LOG_MAX 8192 >> +#define CONSOLE_LOG_MAX 1024 >> >> /* printk's without a loglevel use this.. */ >> #define MESSAGE_LOGLEVEL_DEFAULT CONFIG_MESSAGE_LOGLEVEL_DEFAULT >> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c >> index ec2174882b8e..5faf9c0db171 100644 >> --- a/kernel/printk/printk.c >> +++ b/kernel/printk/printk.c >> @@ -410,7 +410,7 @@ static u64 clear_seq; >> #else >> #define PREFIX_MAX 32 >> #endif >> -#define LOG_LINE_MAX (1024 - PREFIX_MAX) >> +#define LOG_LINE_MAX (CONSOLE_LOG_MAX - PREFIX_MAX) > > CONSOLE_LOG_MAX defines size of buffers that are written by > record_print_text(). We must make sure that all stored > messages can actually get printed even with the trailing '\0'. > > We should limit the stored messages by: > > /* > * Console log buffer needs extra space for the trailing '\0', > * see reccord_print_text(). > */ > #define LOG_LINE_MAX (CONSOLE_LOG_MAX - PREFIX_MAX - 1) > > It should not be a big problem. The PREFIX_MAX size has already > increased in the patch, for example, because of the caller ID. > > Does it make sense, please? If we want to make sure "all stored messages can actually get printed", then CONSOLE_LOG_MAX needs to be set to: PREFIX_MAX * LOG_LINE_MAX + 1 and we should be specifying LOG_LINE_MAX instead of CONSOLE_LOG_MAX. record_print_text() adds up to PREFIX_MAX for every '\n' in the message. I was initially confused by this, which led to my patch [0] to fix it. But then I realized that the buffer is way too small anyway. If we want to fix the issue, then LOG_LINE_MAX needs to be much larger. IMO it makes no sense to do the -1 change because the buffer is too small anyway. John Ogness [0] https://lkml.kernel.org/r/20210120194106.26441-2-john.ogness@linutronix.de