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 C0430C433FE for ; Wed, 13 Oct 2021 01:53:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A42B36109E for ; Wed, 13 Oct 2021 01:53:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233564AbhJMBzL (ORCPT ); Tue, 12 Oct 2021 21:55:11 -0400 Received: from out30-130.freemail.mail.aliyun.com ([115.124.30.130]:55501 "EHLO out30-130.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231543AbhJMBzK (ORCPT ); Tue, 12 Oct 2021 21:55:10 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R191e4;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=31;SR=0;TI=SMTPD_---0UrdeUV._1634089981; Received: from testdeMacBook-Pro.local(mailfrom:yun.wang@linux.alibaba.com fp:SMTPD_---0UrdeUV._1634089981) by smtp.aliyun-inc.com(127.0.0.1); Wed, 13 Oct 2021 09:53:02 +0800 Subject: Re: [PATCH 1/2] ftrace: disable preemption on the testing of recursion To: Steven Rostedt , Miroslav Benes Cc: 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 , 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: <8c7de46d-9869-aa5e-2bb9-5dbc2eda395e@linux.alibaba.com> <20211012082920.1f8d6557@gandalf.local.home> From: =?UTF-8?B?546L6LSH?= Message-ID: <6ca59cdd-e378-b8c6-7ac6-472568f1af97@linux.alibaba.com> Date: Wed, 13 Oct 2021 09:52:16 +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: <20211012082920.1f8d6557@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: linux-parisc@vger.kernel.org On 2021/10/12 下午8:29, Steven Rostedt wrote: > On Tue, 12 Oct 2021 14:24:43 +0200 (CEST) > Miroslav Benes wrote: > >>> +++ b/kernel/livepatch/patch.c >>> @@ -52,11 +52,6 @@ static void notrace klp_ftrace_handler(unsigned long ip, >>> bit = ftrace_test_recursion_trylock(ip, parent_ip); >>> if (WARN_ON_ONCE(bit < 0)) >>> return; >>> - /* >>> - * A variant of synchronize_rcu() is used to allow patching functions >>> - * where RCU is not watching, see klp_synchronize_transition(). >>> - */ >>> - preempt_disable_notrace(); >>> >>> func = list_first_or_null_rcu(&ops->func_stack, struct klp_func, >>> stack_node); >>> @@ -120,7 +115,6 @@ static void notrace klp_ftrace_handler(unsigned long ip, >>> klp_arch_set_pc(fregs, (unsigned long)func->new_func); >>> >>> unlock: >>> - preempt_enable_notrace(); >>> ftrace_test_recursion_unlock(bit); >>> } >> >> I don't like this change much. We have preempt_disable there not because >> of ftrace_test_recursion, but because of RCU. ftrace_test_recursion was >> added later. Yes, it would work with the change, but it would also hide >> things which should not be hidden in my opinion. > > Agreed, but I believe the change is fine, but requires a nice comment to > explain what you said above. > > Thus, before the "ftrace_test_recursion_trylock()" we need: > > /* > * 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. > */ Will be in v2 too :-) Regards, Michael Wang > > -- Steve > 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 B0DFBC433F5 for ; Wed, 13 Oct 2021 01:53:31 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 7668060F23 for ; Wed, 13 Oct 2021 01:53:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 7668060F23 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date: Message-ID:From:References:Cc:To:Subject:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Owner; bh=wnzkioRrfts6oyIMHSGfRG5XUem0eu6r2aoS8SUv4QY=; b=O/W8I5RmXeHFCyKdbFt8GJltoM jhiMtSNTXiTqjs7jByUzMYD/T3gOetIHH9lOOn/KZwuX1MPpKE1aXohpoFxw65AffGKktJZmgsJIb 2EkHUvfm1kEZYd8y3lps10Cr6rOoqNrWxMIYHqcu/QArzqNQ0M+ZjS53JfocOp+3v3umPvdCtt7TX knsnpzGVFLlCsYK7r+Vb2BH6C38EZrhFlAx5pH0gtLfZY1rLNvBGXwdPV8AFVuhaK4s4erbXGYCNz a+BdCCsUN7hksuUyi6wNmj/xw9P4SV7ncDxjmArGGNFjQAWhV82orhhBcCI/gQzoAPqeLowRP+79A hHikhL7Q==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1maTSE-00EbcR-Hb; Wed, 13 Oct 2021 01:53:14 +0000 Received: from out30-42.freemail.mail.aliyun.com ([115.124.30.42]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1maTS8-00EbZA-P2 for linux-riscv@lists.infradead.org; Wed, 13 Oct 2021 01:53:12 +0000 X-Alimail-AntiSpam: AC=PASS; BC=-1|-1; BR=01201311R191e4; 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=31; SR=0; TI=SMTPD_---0UrdeUV._1634089981; Received: from testdeMacBook-Pro.local(mailfrom:yun.wang@linux.alibaba.com fp:SMTPD_---0UrdeUV._1634089981) by smtp.aliyun-inc.com(127.0.0.1); Wed, 13 Oct 2021 09:53:02 +0800 Subject: Re: [PATCH 1/2] ftrace: disable preemption on the testing of recursion To: Steven Rostedt , Miroslav Benes Cc: 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 , 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: <8c7de46d-9869-aa5e-2bb9-5dbc2eda395e@linux.alibaba.com> <20211012082920.1f8d6557@gandalf.local.home> From: =?UTF-8?B?546L6LSH?= Message-ID: <6ca59cdd-e378-b8c6-7ac6-472568f1af97@linux.alibaba.com> Date: Wed, 13 Oct 2021 09:52:16 +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: <20211012082920.1f8d6557@gandalf.local.home> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211012_185308_994107_01F0221B X-CRM114-Status: GOOD ( 15.43 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org CgpPbiAyMDIxLzEwLzEyIOS4i+WNiDg6MjksIFN0ZXZlbiBSb3N0ZWR0IHdyb3RlOgo+IE9uIFR1 ZSwgMTIgT2N0IDIwMjEgMTQ6MjQ6NDMgKzAyMDAgKENFU1QpCj4gTWlyb3NsYXYgQmVuZXMgPG1i ZW5lc0BzdXNlLmN6PiB3cm90ZToKPiAKPj4+ICsrKyBiL2tlcm5lbC9saXZlcGF0Y2gvcGF0Y2gu Ywo+Pj4gQEAgLTUyLDExICs1Miw2IEBAIHN0YXRpYyB2b2lkIG5vdHJhY2Uga2xwX2Z0cmFjZV9o YW5kbGVyKHVuc2lnbmVkIGxvbmcgaXAsCj4+PiAgCWJpdCA9IGZ0cmFjZV90ZXN0X3JlY3Vyc2lv bl90cnlsb2NrKGlwLCBwYXJlbnRfaXApOwo+Pj4gIAlpZiAoV0FSTl9PTl9PTkNFKGJpdCA8IDAp KQo+Pj4gIAkJcmV0dXJuOwo+Pj4gLQkvKgo+Pj4gLQkgKiBBIHZhcmlhbnQgb2Ygc3luY2hyb25p emVfcmN1KCkgaXMgdXNlZCB0byBhbGxvdyBwYXRjaGluZyBmdW5jdGlvbnMKPj4+IC0JICogd2hl cmUgUkNVIGlzIG5vdCB3YXRjaGluZywgc2VlIGtscF9zeW5jaHJvbml6ZV90cmFuc2l0aW9uKCku Cj4+PiAtCSAqLwo+Pj4gLQlwcmVlbXB0X2Rpc2FibGVfbm90cmFjZSgpOwo+Pj4KPj4+ICAJZnVu YyA9IGxpc3RfZmlyc3Rfb3JfbnVsbF9yY3UoJm9wcy0+ZnVuY19zdGFjaywgc3RydWN0IGtscF9m dW5jLAo+Pj4gIAkJCQkgICAgICBzdGFja19ub2RlKTsKPj4+IEBAIC0xMjAsNyArMTE1LDYgQEAg c3RhdGljIHZvaWQgbm90cmFjZSBrbHBfZnRyYWNlX2hhbmRsZXIodW5zaWduZWQgbG9uZyBpcCwK Pj4+ICAJa2xwX2FyY2hfc2V0X3BjKGZyZWdzLCAodW5zaWduZWQgbG9uZylmdW5jLT5uZXdfZnVu Yyk7Cj4+Pgo+Pj4gIHVubG9jazoKPj4+IC0JcHJlZW1wdF9lbmFibGVfbm90cmFjZSgpOwo+Pj4g IAlmdHJhY2VfdGVzdF9yZWN1cnNpb25fdW5sb2NrKGJpdCk7Cj4+PiAgfSAgCj4+Cj4+IEkgZG9u J3QgbGlrZSB0aGlzIGNoYW5nZSBtdWNoLiBXZSBoYXZlIHByZWVtcHRfZGlzYWJsZSB0aGVyZSBu b3QgYmVjYXVzZSAKPj4gb2YgZnRyYWNlX3Rlc3RfcmVjdXJzaW9uLCBidXQgYmVjYXVzZSBvZiBS Q1UuIGZ0cmFjZV90ZXN0X3JlY3Vyc2lvbiB3YXMgCj4+IGFkZGVkIGxhdGVyLiBZZXMsIGl0IHdv dWxkIHdvcmsgd2l0aCB0aGUgY2hhbmdlLCBidXQgaXQgd291bGQgYWxzbyBoaWRlIAo+PiB0aGlu Z3Mgd2hpY2ggc2hvdWxkIG5vdCBiZSBoaWRkZW4gaW4gbXkgb3Bpbmlvbi4KPiAKPiBBZ3JlZWQs IGJ1dCBJIGJlbGlldmUgdGhlIGNoYW5nZSBpcyBmaW5lLCBidXQgcmVxdWlyZXMgYSBuaWNlIGNv bW1lbnQgdG8KPiBleHBsYWluIHdoYXQgeW91IHNhaWQgYWJvdmUuCj4gCj4gVGh1cywgYmVmb3Jl IHRoZSAiZnRyYWNlX3Rlc3RfcmVjdXJzaW9uX3RyeWxvY2soKSIgd2UgbmVlZDoKPiAKPiAJLyoK PiAJICogVGhlIGZ0cmFjZV90ZXN0X3JlY3Vyc2lvbl90cnlsb2NrKCkgd2lsbCBkaXNhYmxlIHBy ZWVtcHRpb24sCj4gCSAqIHdoaWNoIGlzIHJlcXVpcmVkIGZvciB0aGUgdmFyaWFudCBvZiBzeW5j aHJvbml6ZV9yY3UoKSB0aGF0IGlzCj4gCSAqIHVzZWQgdG8gYWxsb3cgcGF0Y2hpbmcgZnVuY3Rp b25zIHdoZXJlIFJDVSBpcyBub3Qgd2F0Y2hpbmcuCj4gCSAqIFNlZSBrbHBfc3luY2hyb25pemVf dHJhbnNpdGlvbigpIGZvciBtb3JlIGRldGFpbHMuCj4gCSAqLwoKV2lsbCBiZSBpbiB2MiB0b28g Oi0pCgpSZWdhcmRzLApNaWNoYWVsIFdhbmcKCj4gCj4gLS0gU3RldmUKPiAKCl9fX19fX19fX19f X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fCmxpbnV4LXJpc2N2IG1haWxpbmcg bGlzdApsaW51eC1yaXNjdkBsaXN0cy5pbmZyYWRlYWQub3JnCmh0dHA6Ly9saXN0cy5pbmZyYWRl YWQub3JnL21haWxtYW4vbGlzdGluZm8vbGludXgtcmlzY3YK 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 2C28BC433F5 for ; Wed, 13 Oct 2021 01:53:49 +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 9DCB660E52 for ; Wed, 13 Oct 2021 01:53:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 9DCB660E52 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 4HTbDB6lZkz304x for ; Wed, 13 Oct 2021 12:53:46 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=linux.alibaba.com (client-ip=115.124.30.54; helo=out30-54.freemail.mail.aliyun.com; envelope-from=yun.wang@linux.alibaba.com; receiver=) Received: from out30-54.freemail.mail.aliyun.com (out30-54.freemail.mail.aliyun.com [115.124.30.54]) (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 4HTbCj1xsDz2yK3 for ; Wed, 13 Oct 2021 12:53:20 +1100 (AEDT) X-Alimail-AntiSpam: AC=PASS; BC=-1|-1; BR=01201311R191e4; 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=31; SR=0; TI=SMTPD_---0UrdeUV._1634089981; Received: from testdeMacBook-Pro.local(mailfrom:yun.wang@linux.alibaba.com fp:SMTPD_---0UrdeUV._1634089981) by smtp.aliyun-inc.com(127.0.0.1); Wed, 13 Oct 2021 09:53:02 +0800 Subject: Re: [PATCH 1/2] ftrace: disable preemption on the testing of recursion To: Steven Rostedt , Miroslav Benes References: <8c7de46d-9869-aa5e-2bb9-5dbc2eda395e@linux.alibaba.com> <20211012082920.1f8d6557@gandalf.local.home> From: =?UTF-8?B?546L6LSH?= Message-ID: <6ca59cdd-e378-b8c6-7ac6-472568f1af97@linux.alibaba.com> Date: Wed, 13 Oct 2021 09:52:16 +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: <20211012082920.1f8d6557@gandalf.local.home> 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, Paul Mackerras , Joe Lawrence , Helge Deller , x86@kernel.org, linux-csky@vger.kernel.org, Ingo Molnar , Petr Mladek , Albert Ou , Jiri Kosina , Nicholas Piggin , Borislav Petkov , Josh Poimboeuf , Thomas Gleixner , linux-parisc@vger.kernel.org, linux-kernel@vger.kernel.org, Palmer Dabbelt , Masami Hiramatsu , Colin Ian King , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 2021/10/12 下午8:29, Steven Rostedt wrote: > On Tue, 12 Oct 2021 14:24:43 +0200 (CEST) > Miroslav Benes wrote: > >>> +++ b/kernel/livepatch/patch.c >>> @@ -52,11 +52,6 @@ static void notrace klp_ftrace_handler(unsigned long ip, >>> bit = ftrace_test_recursion_trylock(ip, parent_ip); >>> if (WARN_ON_ONCE(bit < 0)) >>> return; >>> - /* >>> - * A variant of synchronize_rcu() is used to allow patching functions >>> - * where RCU is not watching, see klp_synchronize_transition(). >>> - */ >>> - preempt_disable_notrace(); >>> >>> func = list_first_or_null_rcu(&ops->func_stack, struct klp_func, >>> stack_node); >>> @@ -120,7 +115,6 @@ static void notrace klp_ftrace_handler(unsigned long ip, >>> klp_arch_set_pc(fregs, (unsigned long)func->new_func); >>> >>> unlock: >>> - preempt_enable_notrace(); >>> ftrace_test_recursion_unlock(bit); >>> } >> >> I don't like this change much. We have preempt_disable there not because >> of ftrace_test_recursion, but because of RCU. ftrace_test_recursion was >> added later. Yes, it would work with the change, but it would also hide >> things which should not be hidden in my opinion. > > Agreed, but I believe the change is fine, but requires a nice comment to > explain what you said above. > > Thus, before the "ftrace_test_recursion_trylock()" we need: > > /* > * 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. > */ Will be in v2 too :-) Regards, Michael Wang > > -- Steve >