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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 EBF15C32789 for ; Tue, 6 Nov 2018 09:56:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BC1292085B for ; Tue, 6 Nov 2018 09:56:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BC1292085B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=i-love.sakura.ne.jp Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387652AbeKFTUc (ORCPT ); Tue, 6 Nov 2018 14:20:32 -0500 Received: from www262.sakura.ne.jp ([202.181.97.72]:35988 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387552AbeKFTUc (ORCPT ); Tue, 6 Nov 2018 14:20:32 -0500 Received: from fsav106.sakura.ne.jp (fsav106.sakura.ne.jp [27.133.134.233]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id wA69u5uY021194; Tue, 6 Nov 2018 18:56:05 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav106.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav106.sakura.ne.jp); Tue, 06 Nov 2018 18:56:05 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav106.sakura.ne.jp) Received: from [192.168.1.8] (softbank060157065137.bbtec.net [60.157.65.137]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id wA69u5FW021189 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Tue, 6 Nov 2018 18:56:05 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: [PATCH 3/3] lockdep: Use line-buffered printk() for lockdep messages. To: Petr Mladek , Peter Zijlstra Cc: Sergey Senozhatsky , Sergey Senozhatsky , Dmitriy Vyukov , Steven Rostedt , Alexander Potapenko , Fengguang Wu , Josh Poimboeuf , LKML , Linus Torvalds , Andrew Morton , linux-mm@kvack.org, Ingo Molnar , Will Deacon References: <1541165517-3557-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <1541165517-3557-3-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <20181102133629.GN3178@hirez.programming.kicks-ass.net> <20181106083856.lhmibz6vrgtkqsj7@pathway.suse.cz> From: Tetsuo Handa Message-ID: Date: Tue, 6 Nov 2018 18:56:03 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20181106083856.lhmibz6vrgtkqsj7@pathway.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018/11/06 17:38, Petr Mladek wrote: > If you would want to avoid buffering, you could set the number > of buffers to zero. Then it would always fallback to > the direct printk(). 1 lock held by swapper/1/0: #0: ( rcu_read_lock ){....} , at: trace_call_bpf+0xf8/0x640 kernel/trace/bpf_trace.c:46 is not welcomed and 1 lock held by swapper/1/0: #0: (rcu_read_lock){....}, at: trace_call_bpf+0xf8/0x640 kernel/trace/bpf_trace.c:46 is welcomed. If you want to avoid fallback to direct printk(), please allocate on-stack buffer with appropriate size. Since lockdep splat may happen when kernel stack is already tight, blindly allocating large buffer on the stack is not good.