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 X-Spam-Level: X-Spam-Status: No, score=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DD008C43381 for ; Fri, 15 Feb 2019 01:35:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9398321B68 for ; Fri, 15 Feb 2019 01:35:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=synopsys.com header.i=@synopsys.com header.b="TReKCFle" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730795AbfBOBfq (ORCPT ); Thu, 14 Feb 2019 20:35:46 -0500 Received: from smtprelay.synopsys.com ([198.182.60.111]:49408 "EHLO smtprelay.synopsys.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728905AbfBOBfq (ORCPT ); Thu, 14 Feb 2019 20:35:46 -0500 Received: from mailhost.synopsys.com (dc8-mailhost1.synopsys.com [10.13.135.209]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtprelay.synopsys.com (Postfix) with ESMTPS id B376F10C1039; Thu, 14 Feb 2019 17:35:45 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=synopsys.com; s=mail; t=1550194545; bh=IBqm5qNukl2ROXiPY4aT5wo5lRAbddJ8leJA9h5MEGc=; h=Subject:To:CC:References:From:Date:In-Reply-To:From; b=TReKCFletXfXxZ2HF7Vv6+pDU1nQvbRZU6jpc8uBi4qNA/H9z9S4KTaDRQcX8rKS4 jZeLr/awoDOpMN9R7oTUiohsU65m961S7shDVkLQWH6cK9CAo5gWFkL3j3t/LlInt1 F0rA03bLvgpuM2ZsBsmdyV66iEynsd8ghg2quHdmMCbKo0Of4vNQY5tbKLKOB2At6w 5YpxK5foFx+7+/waGYjmQ7dqjU8I/qxfZCiZVG70MJIEVPHB4zEQnW6uzIfMuQpqvh kOK6nq6YdvaZDuezbwQPvtPMkP8fz1wOOQfH85goJuD/R71a+urIuRzitWpe26GF1b emTaRn+88AfRg== Received: from US01WXQAHTC1.internal.synopsys.com (us01wxqahtc1.internal.synopsys.com [10.12.238.230]) (using TLSv1.2 with cipher AES128-SHA256 (128/128 bits)) (No client certificate requested) by mailhost.synopsys.com (Postfix) with ESMTPS id 34D1FA005A; Fri, 15 Feb 2019 01:35:36 +0000 (UTC) Received: from IN01WEHTCA.internal.synopsys.com (10.144.199.104) by US01WXQAHTC1.internal.synopsys.com (10.12.238.230) with Microsoft SMTP Server (TLS) id 14.3.408.0; Thu, 14 Feb 2019 17:34:40 -0800 Received: from IN01WEHTCB.internal.synopsys.com (10.144.199.105) by IN01WEHTCA.internal.synopsys.com (10.144.199.103) with Microsoft SMTP Server (TLS) id 14.3.408.0; Fri, 15 Feb 2019 07:04:42 +0530 Received: from [10.10.161.59] (10.10.161.59) by IN01WEHTCB.internal.synopsys.com (10.144.199.243) with Microsoft SMTP Server (TLS) id 14.3.408.0; Fri, 15 Feb 2019 07:04:43 +0530 Subject: Re: [PATCH] ARC: Explicitly set ARCH_SLAB_MINALIGN = 8 To: Alexey Brodkin , Peter Zijlstra CC: David Laight , "linux-snps-arc@lists.infradead.org" , Arnd Bergmann , "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" , Mark Rutland Newsgroups: gmane.linux.kernel.stable,gmane.linux.kernel.arc,gmane.linux.kernel References: <20190208105519.26750-1-abrodkin@synopsys.com> <81017fe4-b31f-4942-e822-a7b70008b74d@synopsys.com> <20190213125651.GP32494@hirez.programming.kicks-ass.net> <4881796E12491D4BB15146FE0209CE64681DB01F@DE02WEMBXB.internal.synopsys.com> From: Vineet Gupta Openpgp: preference=signencrypt Autocrypt: addr=vgupta@synopsys.com; keydata= mQINBFEffBMBEADIXSn0fEQcM8GPYFZyvBrY8456hGplRnLLFimPi/BBGFA24IR+B/Vh/EFk B5LAyKuPEEbR3WSVB1x7TovwEErPWKmhHFbyugdCKDv7qWVj7pOB+vqycTG3i16eixB69row lDkZ2RQyy1i/wOtHt8Kr69V9aMOIVIlBNjx5vNOjxfOLux3C0SRl1veA8sdkoSACY3McOqJ8 zR8q1mZDRHCfz+aNxgmVIVFN2JY29zBNOeCzNL1b6ndjU73whH/1hd9YMx2Sp149T8MBpkuQ cFYUPYm8Mn0dQ5PHAide+D3iKCHMupX0ux1Y6g7Ym9jhVtxq3OdUI5I5vsED7NgV9c8++baM 7j7ext5v0l8UeulHfj4LglTaJIvwbUrCGgtyS9haKlUHbmey/af1j0sTrGxZs1ky1cTX7yeF nSYs12GRiVZkh/Pf3nRLkjV+kH++ZtR1GZLqwamiYZhAHjo1Vzyl50JT9EuX07/XTyq/Bx6E dcJWr79ZphJ+mR2HrMdvZo3VSpXEgjROpYlD4GKUApFxW6RrZkvMzuR2bqi48FThXKhFXJBd JiTfiO8tpXaHg/yh/V9vNQqdu7KmZIuZ0EdeZHoXe+8lxoNyQPcPSj7LcmE6gONJR8ZqAzyk F5voeRIy005ZmJJ3VOH3Gw6Gz49LVy7Kz72yo1IPHZJNpSV5xwARAQABtCpWaW5lZXQgR3Vw dGEgKGFsaWFzKSA8dmd1cHRhQHN5bm9wc3lzLmNvbT6JAj4EEwECACgCGwMGCwkIBwMCBhUI AgkKCwQWAgMBAh4BAheABQJbBYpwBQkLx0HcAAoJEGnX8d3iisJeChAQAMR2UVbJyydOv3aV jmqP47gVFq4Qml1weP5z6czl1I8n37bIhdW0/lV2Zll+yU1YGpMgdDTHiDqnGWi4pJeu4+c5 xsI/VqkH6WWXpfruhDsbJ3IJQ46//jb79ogjm6VVeGlOOYxx/G/RUUXZ12+CMPQo7Bv+Jb+t NJnYXYMND2Dlr2TiRahFeeQo8uFbeEdJGDsSIbkOV0jzrYUAPeBwdN8N0eOB19KUgPqPAC4W HCg2LJ/o6/BImN7bhEFDFu7gTT0nqFVZNXlOw4UcGGpM3dq/qu8ZgRE0turY9SsjKsJYKvg4 djAaOh7H9NJK72JOjUhXY/sMBwW5vnNwFyXCB5t4ZcNxStoxrMtyf35synJVinFy6wCzH3eJ XYNfFsv4gjF3l9VYmGEJeI8JG/ljYQVjsQxcrU1lf8lfARuNkleUL8Y3rtxn6eZVtAlJE8q2 hBgu/RUj79BKnWEPFmxfKsaj8of+5wubTkP0I5tXh0akKZlVwQ3lbDdHxznejcVCwyjXBSny d0+qKIXX1eMh0/5sDYM06/B34rQyq9HZVVPRHdvsfwCU0s3G+5Fai02mK68okr8TECOzqZtG cuQmkAeegdY70Bpzfbwxo45WWQq8dSRURA7KDeY5LutMphQPIP2syqgIaiEatHgwetyVCOt6 tf3ClCidHNaGky9KcNSQuQINBFEffBMBEADXZ2pWw4Regpfw+V+Vr6tvZFRl245PV9rWFU72 xNuvZKq/WE3xMu+ZE7l2JKpSjrEoeOHejtT0cILeQ/Yhf2t2xAlrBLlGOMmMYKK/K0Dc2zf0 MiPRbW/NCivMbGRZdhAAMx1bpVhInKjU/6/4mT7gcE57Ep0tl3HBfpxCK8RRlZc3v8BHOaEf cWSQD7QNTZK/kYJo+Oyux+fzyM5TTuKAaVE63NHCgWtFglH2vt2IyJ1XoPkAMueLXay6enSK Nci7qAG2UwicyVDCK9AtEub+ps8NakkeqdSkDRp5tQldJbfDaMXuWxJuPjfSojHIAbFqP6Qa ANXvTCSuBgkmGZ58skeNopasrJA4z7OsKRUBvAnharU82HGemtIa4Z83zotOGNdaBBOHNN2M HyfGLm+kEoccQheH+my8GtbH1a8eRBtxlk4c02ONkq1Vg1EbIzvgi4a56SrENFx4+4sZcm8o ItShAoKGIE/UCkj/jPlWqOcM/QIqJ2bR8hjBny83ONRf2O9nJuEYw9vZAPFViPwWG8tZ7J+R euXKai4DDr+8oFOi/40mIDe/Bat3ftyd+94Z1RxDCngd3Q85bw13t2ttNLw5eHufLIpoEyAh TCLNQ58eT91YGVGvFs39IuH0b8ovVvdkKGInCT59Vr0MtfgcsqpDxWQXJXYZYTFHd3/RswAR AQABiQIlBBgBAgAPAhsMBQJbBYpwBQkLx0HdAAoJEGnX8d3iisJewe8P/36pkZrVTfO+U+Gl 1OQh4m6weozuI8Y98/DHLMxEujKAmRzy+zMHYlIl3WgSih1UMOZ7U84yVZQwXQkLItcwXoih ChKD5D2BKnZYEOLM+7f9DuJuWhXpee80aNPzEaubBYQ7dYt8rcmB7SdRz/yZq3lALOrF/zb6 SRleBh0DiBLP/jKUV74UAYV3OYEDHN9blvhWUEFFE0Z+j96M4/kuRdxvbDmp04Nfx79AmJEn fv1Vvc9CFiWVbBrNPKomIN+JV7a7m2lhbfhlLpUk0zGFDTWcWejl4qz/pCYSoIUU4r/VBsCV ZrOun4vd4cSi/yYJRY4kaAJGCL5k7qhflL2tgldUs+wERH8ZCzimWVDBzHTBojz0Ff3w2+gY 6FUbAJBrBZANkymPpdAB/lTsl8D2ZRWyy90f4VVc8LB/QIWY/GiS2towRXQBjHOfkUB1JiEX YH/i93k71mCaKfzKGXTVxObU2I441w7r4vtNlu0sADRHCMUqHmkpkjV1YbnYPvBPFrDBS1V9 OfD9SutXeDjJYe3N+WaLRp3T3x7fYVnkfjQIjDSOdyPWlTzqQv0I3YlUk7KjFrh1rxtrpoYS IQKf5HuMowUNtjyiK2VhA5V2XDqd+ZUT3RqfAPf3Y5HjkhKJRqoIDggUKMUKmXaxCkPGi91T hhqBJlyU6MVUa6vZNv8E Message-ID: Date: Thu, 14 Feb 2019 17:34:29 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <4881796E12491D4BB15146FE0209CE64681DB01F@DE02WEMBXB.internal.synopsys.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.10.161.59] Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On 2/14/19 12:50 AM, Alexey Brodkin wrote: >>>>> I suspect the slab allocator should be returning 8 byte aligned addresses >>>>> on all systems.... >>>> >>>> why ? As I understand it is still not fool proof against the expected alignment of >>>> inner members. There ought to be a better way to enforce all this. >>> >>> I agree that for ARC ARCH_SLAB_MINALIGN should be at least 8. >> >> This issue aside, are there other reasons ? Because making it 8 on ARC is just >> pending the eventuality for later. > > But that's pretty much the same for other 32-bit arches that have 64-bit atomics > like ARM etc. From what I may see from ARM's documentation for LDREXD/SRREXD they > require double-word alignment of data as well. Right LLOCKD/SCONDD (64-bit exclusive load/store) needs 64-bit aligned effective addresses for micro-arch reasons (1 vs 2 cache lines) etc. So lets try to unpack this for me. Say we had. struct foo { int a; atomic64_t b; }; The atomic64_t (which for ARC and most others is u64 __attribute__((aligned(8)) *already ensures* that there a 4 b padding is generated by gcc (I just confirmed with a simple test case). #ifdef DOALIGN__ #define my_u64 __u64 __attribute__((aligned(8))) #else #define my_u64 __u64 #endif struct foo on_heap; printf(%d", &on_heap.b) $ arc-linux-gcc -O2 test.c -DDOALIGN__ -c --save-temps main: mov_s r1,@on_heap+8 <---- mov_s r0,@.LC0 b @printf W/o the alignment attribute (say normal LDD/STD) $ arc-linux-gcc -O2 test.c -c --save-temps main: mov_s r1,@on_heap+4 mov_s r0,@.LC0 b @printf So indeed your patch aligns dynamic structs to 64-bit, ensuring any embedded aligned_u64 to be 64-bit aligned as well. Phew ! > That said if for some reason atomic64_t variable is unaligned execution on > any (or at least most) 32-bit architectures will lead to run-time failure, > i.e. we'll know about it and this will be fixed. > > And what I'm doing by that change (ARCH_SLAB_MINALIGN=8 for ARC) I'm just > working-around peculiarity of ARC ABI. Right. > > Out of curiosity I checked if there're any other occurrences of "alingof(long long)" > and there seems to be a couple of more: > ----------------------------------->8----------------------------- > # git grep alignof | grep "long long" > > ... > > kernel/workqueue.c:5693: WARN_ON(__alignof__(struct pool_workqueue) < __alignof__(long long)); > mm/slab.c:155:#define REDZONE_ALIGN max(BYTES_PER_WORD, __alignof__(unsigned long long)) For ARC, it will be max(4,4) so 4 for others 32-bit,it will be max(4,8) So indeed it makes sense to change it. > mm/slab.c:2034: if (ralign > __alignof__(unsigned long long)) > ----------------------------------->8----------------------------- > > Not really sure how important is "kernel/workqueue.c" part but in case of "mm/slab.c" > shouldn't we use ARCH_SLAB_MINALIGN there instead of that "not very meaningful" __alignof__(long long)?