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 D39CCC433FE for ; Wed, 13 Oct 2021 08:11:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B4A3A61040 for ; Wed, 13 Oct 2021 08:11:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238847AbhJMINW (ORCPT ); Wed, 13 Oct 2021 04:13:22 -0400 Received: from out30-131.freemail.mail.aliyun.com ([115.124.30.131]:46211 "EHLO out30-131.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238736AbhJMINV (ORCPT ); Wed, 13 Oct 2021 04:13:21 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R641e4;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=31;SR=0;TI=SMTPD_---0UrfoBuS_1634112670; Received: from testdeMacBook-Pro.local(mailfrom:yun.wang@linux.alibaba.com fp:SMTPD_---0UrfoBuS_1634112670) by smtp.aliyun-inc.com(127.0.0.1); Wed, 13 Oct 2021 16:11:12 +0800 Subject: Re: [RESEND PATCH v2 1/2] ftrace: disable preemption between ftrace_test_recursion_trylock/unlock() To: Miroslav Benes Cc: Guo Ren , Steven Rostedt , 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 , Colin Ian King , 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: <75ee86ac-02f2-d687-ab1e-9c8c33032495@linux.alibaba.com> From: =?UTF-8?B?546L6LSH?= Message-ID: Date: Wed, 13 Oct 2021 16:11:10 +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 Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On 2021/10/13 下午3:55, Miroslav Benes wrote: >> diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h >> index a9f9c57..101e1fb 100644 >> --- a/include/linux/trace_recursion.h >> +++ b/include/linux/trace_recursion.h >> @@ -208,13 +208,29 @@ static __always_inline void trace_clear_recursion(int bit) >> * Use this for ftrace callbacks. This will detect if the function >> * tracing recursed in the same context (normal vs interrupt), >> * >> + * The ftrace_test_recursion_trylock() will disable preemption, >> + * which is required for the variant of synchronize_rcu() that is >> + * used to allow patching functions where RCU is not watching. >> + * See klp_synchronize_transition() for more details. >> + * > > I think that you misunderstood. Steven proposed to put the comment before > ftrace_test_recursion_trylock() call site in klp_ftrace_handler(). Oh, I see... thanks for pointing out :-) > >> * Returns: -1 if a recursion happened. [snip] >> } > > Side note... the comment will eventually conflict with peterz's > https://lore.kernel.org/all/20210929152429.125997206@infradead.org/. Steven, would you like to share your opinion on this patch? If klp_synchronize_transition() will be removed anyway, the comments will be meaningless and we can just drop it :-P Regards, Michael Wang > > Miroslav >