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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E7B74C433FE for ; Wed, 27 Oct 2021 01:55:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D215C61040 for ; Wed, 27 Oct 2021 01:55:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237692AbhJ0B5y (ORCPT ); Tue, 26 Oct 2021 21:57:54 -0400 Received: from out4436.biz.mail.alibaba.com ([47.88.44.36]:31072 "EHLO out4436.biz.mail.alibaba.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236313AbhJ0B5x (ORCPT ); Tue, 26 Oct 2021 21:57:53 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R441e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04423;MF=yun.wang@linux.alibaba.com;NM=1;PH=DS;RN=30;SR=0;TI=SMTPD_---0UtpFhNO_1635299711; Received: from testdeMacBook-Pro.local(mailfrom:yun.wang@linux.alibaba.com fp:SMTPD_---0UtpFhNO_1635299711) by smtp.aliyun-inc.com(127.0.0.1); Wed, 27 Oct 2021 09:55:13 +0800 Subject: Re: [PATCH v5 1/2] ftrace: disable preemption when recursion locked To: Steven Rostedt Cc: Miroslav Benes , Guo Ren , Ingo Molnar , "James E.J. Bottomley" , Helge Deller , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , Paul Walmsley , Palmer Dabbelt , Albert Ou , Thomas Gleixner , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , Josh Poimboeuf , Jiri Kosina , Petr Mladek , Joe Lawrence , Masami Hiramatsu , "Peter Zijlstra (Intel)" , Nicholas Piggin , Jisheng Zhang , linux-csky@vger.kernel.org, linux-kernel@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, live-patching@vger.kernel.org References: <3ca92dc9-ea04-ddc2-71cd-524bfa5a5721@linux.alibaba.com> <333cecfe-3045-8e0a-0c08-64ff590845ab@linux.alibaba.com> <18ba2a71-e12d-33f7-63fe-2857b2db022c@linux.alibaba.com> <20211026080117.366137a5@gandalf.local.home> From: =?UTF-8?B?546L6LSH?= Message-ID: <3d897161-7b74-944a-f2a0-07311436fbd9@linux.alibaba.com> Date: Wed, 27 Oct 2021 09:54:13 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:78.0) Gecko/20100101 Thunderbird/78.14.0 MIME-Version: 1.0 In-Reply-To: <20211026080117.366137a5@gandalf.local.home> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On 2021/10/26 δΈ‹εˆ8:01, Steven Rostedt wrote: > On Tue, 26 Oct 2021 17:48:10 +0800 > ηŽ‹θ΄‡ wrote: > >>> The two comments should be updated too since Steven removed the "bit == 0" >>> trick. >> >> Could you please give more hint on how will it be correct? >> >> I get the point that bit will no longer be 0, there are only -1 or > 0 now >> so trace_test_and_set_recursion() will disable preemption on bit > 0 and >> trace_clear_recursion() will enabled it since it should only be called when >> bit > 0 (I remember we could use a WARN_ON here now :-P). >> >>> >>>> @@ -178,7 +187,7 @@ static __always_inline void trace_clear_recursion(int bit) >>>> * tracing recursed in the same context (normal vs interrupt), >>>> * >>>> * Returns: -1 if a recursion happened. >>>> - * >= 0 if no recursion >>>> + * > 0 if no recursion. >>>> */ >>>> static __always_inline int ftrace_test_recursion_trylock(unsigned long ip, >>>> unsigned long parent_ip) >>> >>> And this change would not be correct now. >> >> I thought it will no longer return 0 so I change it to > 0, isn't that correct? > > No it is not. I removed the bit + 1 return value, which means it returns the > actual bit now. Which is 0 or more. Ah, the return is bit not val, I must be drunk... My apologize for the stupid comments... I'll send a v6 for this patch only to fix that, please let me know if this is not a good way to fix few lines of comments. Regards, Michael Wang > > -- Steve >