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 18986C433F5 for ; Tue, 26 Oct 2021 09:48:52 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 56E1861039 for ; Tue, 26 Oct 2021 09:48:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 56E1861039 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=lists.ozlabs.org Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4Hdn8K5tH5z2ymZ for ; Tue, 26 Oct 2021 20:48:49 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=linux.alibaba.com (client-ip=115.124.30.130; helo=out30-130.freemail.mail.aliyun.com; envelope-from=yun.wang@linux.alibaba.com; receiver=) Received: from out30-130.freemail.mail.aliyun.com (out30-130.freemail.mail.aliyun.com [115.124.30.130]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4Hdn7s219Bz2xvf for ; Tue, 26 Oct 2021 20:48:22 +1100 (AEDT) X-Alimail-AntiSpam: AC=PASS; BC=-1|-1; BR=01201311R151e4; CH=green; DM=||false|; DS=||; FP=0|-1|-1|-1|0|-1|-1|-1; HT=e01e04357; MF=yun.wang@linux.alibaba.com; NM=1; PH=DS; RN=30; SR=0; TI=SMTPD_---0Utm5zog_1635241690; Received: from testdeMacBook-Pro.local(mailfrom:yun.wang@linux.alibaba.com fp:SMTPD_---0Utm5zog_1635241690) by smtp.aliyun-inc.com(127.0.0.1); Tue, 26 Oct 2021 17:48:12 +0800 Subject: Re: [PATCH v5 1/2] ftrace: disable preemption when recursion locked To: Miroslav Benes References: <3ca92dc9-ea04-ddc2-71cd-524bfa5a5721@linux.alibaba.com> <333cecfe-3045-8e0a-0c08-64ff590845ab@linux.alibaba.com> From: =?UTF-8?B?546L6LSH?= Message-ID: <18ba2a71-e12d-33f7-63fe-2857b2db022c@linux.alibaba.com> Date: Tue, 26 Oct 2021 17:48:10 +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: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Peter Zijlstra \(Intel\)" , Paul Walmsley , "James E.J. Bottomley" , Guo Ren , Jisheng Zhang , "H. Peter Anvin" , live-patching@vger.kernel.org, linux-riscv@lists.infradead.org, Joe Lawrence , Helge Deller , x86@kernel.org, linux-csky@vger.kernel.org, Ingo Molnar , Petr Mladek , Albert Ou , Jiri Kosina , Nicholas Piggin , Borislav Petkov , Steven Rostedt , Josh Poimboeuf , Thomas Gleixner , linux-parisc@vger.kernel.org, linux-kernel@vger.kernel.org, Palmer Dabbelt , Masami Hiramatsu , Paul Mackerras , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Hi, Miroslav On 2021/10/26 下午5:35, Miroslav Benes wrote: > Hi, > >> diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h >> index abe1a50..2bc1522 100644 >> --- a/include/linux/trace_recursion.h >> +++ b/include/linux/trace_recursion.h >> @@ -135,6 +135,9 @@ static __always_inline int trace_get_context_bit(void) >> # define do_ftrace_record_recursion(ip, pip) do { } while (0) >> #endif >> >> +/* >> + * Preemption is promised to be disabled when return bit > 0. >> + */ >> static __always_inline int trace_test_and_set_recursion(unsigned long ip, unsigned long pip, >> int start) >> { >> @@ -162,11 +165,17 @@ static __always_inline int trace_test_and_set_recursion(unsigned long ip, unsign >> current->trace_recursion = val; >> barrier(); >> >> + preempt_disable_notrace(); >> + >> return bit; >> } >> >> +/* >> + * Preemption will be enabled (if it was previously enabled). >> + */ >> static __always_inline void trace_clear_recursion(int bit) >> { >> + preempt_enable_notrace(); >> barrier(); >> trace_recursion_clear(bit); >> } > > 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? Regards, Michael Wang > > Regards > Miroslav >