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[23.128.96.18]) by mx.google.com with ESMTP id g13si440397ejw.130.2020.10.28.14.41.21; Wed, 28 Oct 2020 14:41:45 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726290AbgJ1Bi7 (ORCPT + 99 others); Tue, 27 Oct 2020 21:38:59 -0400 Received: from mail-out.m-online.net ([212.18.0.9]:52644 "EHLO mail-out.m-online.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1833026AbgJ0Xh2 (ORCPT ); Tue, 27 Oct 2020 19:37:28 -0400 Received: from frontend01.mail.m-online.net (unknown [192.168.8.182]) by mail-out.m-online.net (Postfix) with ESMTP id 4CLSmP52JLz1qrf4; Wed, 28 Oct 2020 00:37:25 +0100 (CET) Received: from localhost (dynscan1.mnet-online.de [192.168.6.70]) by mail.m-online.net (Postfix) with ESMTP id 4CLSmP4L4Wz1qxh0; Wed, 28 Oct 2020 00:37:25 +0100 (CET) X-Virus-Scanned: amavisd-new at mnet-online.de Received: from mail.mnet-online.de ([192.168.8.182]) by localhost (dynscan1.mail.m-online.net [192.168.6.70]) (amavisd-new, port 10024) with ESMTP id d_0TcLPL1O-b; Wed, 28 Oct 2020 00:37:24 +0100 (CET) X-Auth-Info: y1E296PKjR1EjwCQjRjly4MXLwtDaL72s0jq/tkD+COt/3N7THhYadhmeT3nZR5p Received: from igel.home (ppp-46-244-161-64.dynamic.mnet-online.de [46.244.161.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.mnet-online.de (Postfix) with ESMTPSA; Wed, 28 Oct 2020 00:37:24 +0100 (CET) Received: by igel.home (Postfix, from userid 1000) id EF9D32C2B09; Wed, 28 Oct 2020 00:37:23 +0100 (CET) From: Andreas Schwab To: Christophe Leroy Cc: Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/3] powerpc/uaccess: Switch __put_user_size_allowed() to __put_user_asm_goto() References: <94ba5a5138f99522e1562dbcdb38d31aa790dc89.1599216721.git.christophe.leroy__44535.5968013004$1599217383$gmane$org@csgroup.eu> <87mu079ron.fsf@igel.home> X-Yow: ...I think I'm having an overnight sensation right now!! Date: Wed, 28 Oct 2020 00:37:23 +0100 In-Reply-To: <87mu079ron.fsf@igel.home> (Andreas Schwab's message of "Wed, 28 Oct 2020 00:26:16 +0100") Message-ID: <87imav9r64.fsf@igel.home> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Okt 28 2020, Andreas Schwab wrote: > On Sep 04 2020, Christophe Leroy wrote: > >> __put_user_asm_goto() provides more flexibility to GCC and avoids using >> a local variable to tell if the write succeeded or not. >> GCC can then avoid implementing a cmp in the fast path. > > That breaks CLONE_CHILD_SETTID. I'm getting an assertion failure in > __libc_fork (THREAD_GETMEM (self, tid) != ppid). This is what schedule_tail now looks like. As you can see, put_user has become a nop: 000000000000455c <.schedule_tail>: 455c: 7c 08 02 a6 mflr r0 4560: f8 01 00 10 std r0,16(r1) 4564: f8 21 ff 91 stdu r1,-112(r1) 4568: 4b ff cd 4d bl 12b4 <.finish_task_switch> 456c: 4b ff c0 99 bl 604 <.balance_callback> 4570: e8 6d 01 88 ld r3,392(r13) 4574: e9 23 06 b0 ld r9,1712(r3) 4578: 2f a9 00 00 cmpdi cr7,r9,0 457c: 41 9e 00 14 beq cr7,4590 <.schedule_tail+0x34> 4580: 38 80 00 00 li r4,0 4584: 38 a0 00 00 li r5,0 4588: 48 00 00 01 bl 4588 <.schedule_tail+0x2c> 4588: R_PPC64_REL24 .__task_pid_nr_ns 458c: 60 00 00 00 nop 4590: 48 00 00 01 bl 4590 <.schedule_tail+0x34> 4590: R_PPC64_REL24 .calculate_sigpending 4594: 60 00 00 00 nop 4598: 38 21 00 70 addi r1,r1,112 459c: e8 01 00 10 ld r0,16(r1) 45a0: 7c 08 03 a6 mtlr r0 45a4: 4e 80 00 20 blr This is schedule_tail in 5.9: 000000000000455c <.schedule_tail>: 455c: 7c 08 02 a6 mflr r0 4560: fb c1 ff f0 std r30,-16(r1) 4564: fb e1 ff f8 std r31,-8(r1) 4568: f8 01 00 10 std r0,16(r1) 456c: f8 21 ff 81 stdu r1,-128(r1) 4570: 4b ff cd 45 bl 12b4 <.finish_task_switch> 4574: 4b ff c0 91 bl 604 <.balance_callback> 4578: eb cd 01 88 ld r30,392(r13) 457c: eb fe 06 b0 ld r31,1712(r30) 4580: 2f bf 00 00 cmpdi cr7,r31,0 4584: 41 9e 00 2c beq cr7,45b0 <.schedule_tail+0x54> 4588: 7f c3 f3 78 mr r3,r30 458c: 38 80 00 00 li r4,0 4590: 38 a0 00 00 li r5,0 4594: 48 00 00 01 bl 4594 <.schedule_tail+0x38> 4594: R_PPC64_REL24 .__task_pid_nr_ns 4598: 60 00 00 00 nop 459c: e9 3e 0a b8 ld r9,2744(r30) 45a0: 7f bf 48 40 cmpld cr7,r31,r9 45a4: 41 9d 00 0c bgt cr7,45b0 <.schedule_tail+0x54> 45a8: 2b a9 00 03 cmpldi cr7,r9,3 45ac: 41 9d 00 14 bgt cr7,45c0 <.schedule_tail+0x64> 45b0: 48 00 00 01 bl 45b0 <.schedule_tail+0x54> 45b0: R_PPC64_REL24 .calculate_sigpending 45b4: 60 00 00 00 nop 45b8: 38 21 00 80 addi r1,r1,128 45bc: 48 00 00 00 b 45bc <.schedule_tail+0x60> 45bc: R_PPC64_REL24 _restgpr0_30 45c0: 39 20 00 00 li r9,0 45c4: 90 7f 00 00 stw r3,0(r31) 45c8: 4b ff ff e8 b 45b0 <.schedule_tail+0x54> Andreas. -- Andreas Schwab, schwab@linux-m68k.org GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510 2552 DF73 E780 A9DA AEC1 "And now for something completely different."