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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 00E15C433B4 for ; Sat, 10 Apr 2021 02:44:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C7ABB610A2 for ; Sat, 10 Apr 2021 02:44:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233977AbhDJCo3 (ORCPT ); Fri, 9 Apr 2021 22:44:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47002 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229665AbhDJCo0 (ORCPT ); Fri, 9 Apr 2021 22:44:26 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3AE7CC061762; Fri, 9 Apr 2021 19:44:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=kSBfGQGdldHOGZqey2pG91Lm4sBchHdpUdkbO6By1YI=; b=Exz1xebH0z4i/y6qs7XFO141Qk eRdSApUIFaSir1NyVFycHEYEbOXEp95qDIa230dForIUOhOrcL8b410X67OZZNpDdPq7jmGPKucr7 Jm/mNgBVC4BZbhVGO7ZiGnxsB72BAayKt8FYPWcUkpAAo/QYX9jaHmqnmcaOOEaZUAvoCv7+YoC+d azojKss4OD+27TdGNupRux2mmMjSbuKCdgisakoI1PTwZoivDI2KZGt9qSU6szreGgStQJ6HXtug+ 4dyr/8D2BnK5laEKba2tcv99gMP977IVwZBCOGjK+KP98CtMI/JYoGJ42Sjy4kn89qoYCE05lmJgV 2L/4kfhQ==; Received: from willy by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1lV3ab-001Esh-RM; Sat, 10 Apr 2021 02:43:27 +0000 Date: Sat, 10 Apr 2021 03:43:13 +0100 From: Matthew Wilcox To: kernel test robot Cc: linux-mm@kvack.org, kbuild-all@lists.01.org, clang-built-linux@googlegroups.com, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org, Jesper Dangaard Brouer , "David S. Miller" Subject: Bogus struct page layout on 32-bit Message-ID: <20210410024313.GX2531743@casper.infradead.org> References: <20210409185105.188284-3-willy@infradead.org> <202104100656.N7EVvkNZ-lkp@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <202104100656.N7EVvkNZ-lkp@intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Apr 10, 2021 at 06:45:35AM +0800, kernel test robot wrote: > >> include/linux/mm_types.h:274:1: error: static_assert failed due to requirement '__builtin_offsetof(struct page, lru) == __builtin_offsetof(struct folio, lru)' "offsetof(struct page, lru) == offsetof(struct folio, lru)" > FOLIO_MATCH(lru, lru); > include/linux/mm_types.h:272:2: note: expanded from macro 'FOLIO_MATCH' > static_assert(offsetof(struct page, pg) == offsetof(struct folio, fl)) Well, this is interesting. pahole reports: struct page { long unsigned int flags; /* 0 4 */ /* XXX 4 bytes hole, try to pack */ union { struct { struct list_head lru; /* 8 8 */ ... struct folio { union { struct { long unsigned int flags; /* 0 4 */ struct list_head lru; /* 4 8 */ so this assert has absolutely done its job. But why has this assert triggered? Why is struct page layout not what we thought it was? Turns out it's the dma_addr added in 2019 by commit c25fff7171be ("mm: add dma_addr_t to struct page"). On this particular config, it's 64-bit, and ppc32 requires alignment to 64-bit. So the whole union gets moved out by 4 bytes. Unfortunately, we can't just fix this by putting an 'unsigned long pad' in front of it. It still aligns the entire union to 8 bytes, and then it skips another 4 bytes after the pad. We can fix it like this ... +++ b/include/linux/mm_types.h @@ -96,11 +96,12 @@ struct page { unsigned long private; }; struct { /* page_pool used by netstack */ + unsigned long _page_pool_pad; /** * @dma_addr: might require a 64-bit value even on * 32-bit architectures. */ - dma_addr_t dma_addr; + dma_addr_t dma_addr __packed; }; struct { /* slab, slob and slub */ union { but I don't know if GCC is smart enough to realise that dma_addr is now on an 8 byte boundary and it can use a normal instruction to access it, or whether it'll do something daft like use byte loads to access it. We could also do: + dma_addr_t dma_addr __packed __aligned(sizeof(void *)); and I see pahole, at least sees this correctly: struct { long unsigned int _page_pool_pad; /* 4 4 */ dma_addr_t dma_addr __attribute__((__aligned__(4))); /* 8 8 */ } __attribute__((__packed__)) __attribute__((__aligned__(4))); This presumably affects any 32-bit architecture with a 64-bit phys_addr_t / dma_addr_t. Advice, please? 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=-8.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 1544EC433B4 for ; Sat, 10 Apr 2021 02:45:38 +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 347AA610A2 for ; Sat, 10 Apr 2021 02:45:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 347AA610A2 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4FHK9q2vVYz3byX for ; Sat, 10 Apr 2021 12:45:35 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dkim=fail reason="signature verification failed" (2048-bit key; secure) header.d=infradead.org header.i=@infradead.org header.a=rsa-sha256 header.s=casper.20170209 header.b=Exz1xebH; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=none (no SPF record) smtp.mailfrom=infradead.org (client-ip=2001:8b0:10b:1236::1; helo=casper.infradead.org; envelope-from=willy@infradead.org; receiver=) Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; secure) header.d=infradead.org header.i=@infradead.org header.a=rsa-sha256 header.s=casper.20170209 header.b=Exz1xebH; dkim-atps=neutral Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) (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 4FHK9H4G7zz2y8F for ; Sat, 10 Apr 2021 12:45:06 +1000 (AEST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=kSBfGQGdldHOGZqey2pG91Lm4sBchHdpUdkbO6By1YI=; b=Exz1xebH0z4i/y6qs7XFO141Qk eRdSApUIFaSir1NyVFycHEYEbOXEp95qDIa230dForIUOhOrcL8b410X67OZZNpDdPq7jmGPKucr7 Jm/mNgBVC4BZbhVGO7ZiGnxsB72BAayKt8FYPWcUkpAAo/QYX9jaHmqnmcaOOEaZUAvoCv7+YoC+d azojKss4OD+27TdGNupRux2mmMjSbuKCdgisakoI1PTwZoivDI2KZGt9qSU6szreGgStQJ6HXtug+ 4dyr/8D2BnK5laEKba2tcv99gMP977IVwZBCOGjK+KP98CtMI/JYoGJ42Sjy4kn89qoYCE05lmJgV 2L/4kfhQ==; Received: from willy by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1lV3ab-001Esh-RM; Sat, 10 Apr 2021 02:43:27 +0000 Date: Sat, 10 Apr 2021 03:43:13 +0100 From: Matthew Wilcox To: kernel test robot Subject: Bogus struct page layout on 32-bit Message-ID: <20210410024313.GX2531743@casper.infradead.org> References: <20210409185105.188284-3-willy@infradead.org> <202104100656.N7EVvkNZ-lkp@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <202104100656.N7EVvkNZ-lkp@intel.com> 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: kbuild-all@lists.01.org, clang-built-linux@googlegroups.com, Jesper Dangaard Brouer , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Paul Mackerras , linux-fsdevel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, "David S. Miller" , linux-arm-kernel@lists.infradead.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Sat, Apr 10, 2021 at 06:45:35AM +0800, kernel test robot wrote: > >> include/linux/mm_types.h:274:1: error: static_assert failed due to requirement '__builtin_offsetof(struct page, lru) == __builtin_offsetof(struct folio, lru)' "offsetof(struct page, lru) == offsetof(struct folio, lru)" > FOLIO_MATCH(lru, lru); > include/linux/mm_types.h:272:2: note: expanded from macro 'FOLIO_MATCH' > static_assert(offsetof(struct page, pg) == offsetof(struct folio, fl)) Well, this is interesting. pahole reports: struct page { long unsigned int flags; /* 0 4 */ /* XXX 4 bytes hole, try to pack */ union { struct { struct list_head lru; /* 8 8 */ ... struct folio { union { struct { long unsigned int flags; /* 0 4 */ struct list_head lru; /* 4 8 */ so this assert has absolutely done its job. But why has this assert triggered? Why is struct page layout not what we thought it was? Turns out it's the dma_addr added in 2019 by commit c25fff7171be ("mm: add dma_addr_t to struct page"). On this particular config, it's 64-bit, and ppc32 requires alignment to 64-bit. So the whole union gets moved out by 4 bytes. Unfortunately, we can't just fix this by putting an 'unsigned long pad' in front of it. It still aligns the entire union to 8 bytes, and then it skips another 4 bytes after the pad. We can fix it like this ... +++ b/include/linux/mm_types.h @@ -96,11 +96,12 @@ struct page { unsigned long private; }; struct { /* page_pool used by netstack */ + unsigned long _page_pool_pad; /** * @dma_addr: might require a 64-bit value even on * 32-bit architectures. */ - dma_addr_t dma_addr; + dma_addr_t dma_addr __packed; }; struct { /* slab, slob and slub */ union { but I don't know if GCC is smart enough to realise that dma_addr is now on an 8 byte boundary and it can use a normal instruction to access it, or whether it'll do something daft like use byte loads to access it. We could also do: + dma_addr_t dma_addr __packed __aligned(sizeof(void *)); and I see pahole, at least sees this correctly: struct { long unsigned int _page_pool_pad; /* 4 4 */ dma_addr_t dma_addr __attribute__((__aligned__(4))); /* 8 8 */ } __attribute__((__packed__)) __attribute__((__aligned__(4))); This presumably affects any 32-bit architecture with a 64-bit phys_addr_t / dma_addr_t. Advice, please? 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=-8.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 ABBE3C433B4 for ; Sat, 10 Apr 2021 02:50:39 +0000 (UTC) Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (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 3ADFC6102A for ; Sat, 10 Apr 2021 02:50:39 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3ADFC6102A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=desiato.20200630; h=Sender:Content-Transfer-Encoding :Content-Type:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=03dsmwtQ8Kx21/WBA2dwE7phCxlEn2AXpdFbrEOm+OI=; b=LzNZxH7CecvIjbyk2prNK/dYs gqKsFbgLpqs4vXCejO0+ukP+c/bautHQbA914B7UKcFdRqYTHCx0OQcC4UdE870uY27oWDJnMhdpJ P3/B6liOzseTsJGAT0hSHnNJMWv+3kRiEeBJNDdmR6b5ULXoUT8PpSLiyp9CqWSC5fDvTLLjD1LBR Dq9rOI5LXcpgK3ufD4VXw8bgsU1+Xesxb6WSKt+whhmtXOAImF+UWWFuHVdmw0PcQzUa3NpR10Gt1 gZJdCG9BvfEIO0zuQPKj18upOd6vRPwPjzHybQKBRBuWa9o5xbTD/7YsxhF2QOodN6DxQzwtso/v5 3V9WQfevw==; Received: from localhost ([::1] helo=desiato.infradead.org) by desiato.infradead.org with esmtp (Exim 4.94 #2 (Red Hat Linux)) id 1lV3fn-00209C-GE; Sat, 10 Apr 2021 02:48:35 +0000 Received: from casper.infradead.org ([2001:8b0:10b:1236::1]) by desiato.infradead.org with esmtps (Exim 4.94 #2 (Red Hat Linux)) id 1lV3av-001zyu-Tu for linux-arm-kernel@desiato.infradead.org; Sat, 10 Apr 2021 02:43:58 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=kSBfGQGdldHOGZqey2pG91Lm4sBchHdpUdkbO6By1YI=; b=Exz1xebH0z4i/y6qs7XFO141Qk eRdSApUIFaSir1NyVFycHEYEbOXEp95qDIa230dForIUOhOrcL8b410X67OZZNpDdPq7jmGPKucr7 Jm/mNgBVC4BZbhVGO7ZiGnxsB72BAayKt8FYPWcUkpAAo/QYX9jaHmqnmcaOOEaZUAvoCv7+YoC+d azojKss4OD+27TdGNupRux2mmMjSbuKCdgisakoI1PTwZoivDI2KZGt9qSU6szreGgStQJ6HXtug+ 4dyr/8D2BnK5laEKba2tcv99gMP977IVwZBCOGjK+KP98CtMI/JYoGJ42Sjy4kn89qoYCE05lmJgV 2L/4kfhQ==; Received: from willy by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1lV3ab-001Esh-RM; Sat, 10 Apr 2021 02:43:27 +0000 Date: Sat, 10 Apr 2021 03:43:13 +0100 From: Matthew Wilcox To: kernel test robot Cc: linux-mm@kvack.org, kbuild-all@lists.01.org, clang-built-linux@googlegroups.com, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org, Jesper Dangaard Brouer , "David S. Miller" Subject: Bogus struct page layout on 32-bit Message-ID: <20210410024313.GX2531743@casper.infradead.org> References: <20210409185105.188284-3-willy@infradead.org> <202104100656.N7EVvkNZ-lkp@intel.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <202104100656.N7EVvkNZ-lkp@intel.com> X-BeenThere: linux-arm-kernel@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="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Sat, Apr 10, 2021 at 06:45:35AM +0800, kernel test robot wrote: > >> include/linux/mm_types.h:274:1: error: static_assert failed due to requirement '__builtin_offsetof(struct page, lru) == __builtin_offsetof(struct folio, lru)' "offsetof(struct page, lru) == offsetof(struct folio, lru)" > FOLIO_MATCH(lru, lru); > include/linux/mm_types.h:272:2: note: expanded from macro 'FOLIO_MATCH' > static_assert(offsetof(struct page, pg) == offsetof(struct folio, fl)) Well, this is interesting. pahole reports: struct page { long unsigned int flags; /* 0 4 */ /* XXX 4 bytes hole, try to pack */ union { struct { struct list_head lru; /* 8 8 */ ... struct folio { union { struct { long unsigned int flags; /* 0 4 */ struct list_head lru; /* 4 8 */ so this assert has absolutely done its job. But why has this assert triggered? Why is struct page layout not what we thought it was? Turns out it's the dma_addr added in 2019 by commit c25fff7171be ("mm: add dma_addr_t to struct page"). On this particular config, it's 64-bit, and ppc32 requires alignment to 64-bit. So the whole union gets moved out by 4 bytes. Unfortunately, we can't just fix this by putting an 'unsigned long pad' in front of it. It still aligns the entire union to 8 bytes, and then it skips another 4 bytes after the pad. We can fix it like this ... +++ b/include/linux/mm_types.h @@ -96,11 +96,12 @@ struct page { unsigned long private; }; struct { /* page_pool used by netstack */ + unsigned long _page_pool_pad; /** * @dma_addr: might require a 64-bit value even on * 32-bit architectures. */ - dma_addr_t dma_addr; + dma_addr_t dma_addr __packed; }; struct { /* slab, slob and slub */ union { but I don't know if GCC is smart enough to realise that dma_addr is now on an 8 byte boundary and it can use a normal instruction to access it, or whether it'll do something daft like use byte loads to access it. We could also do: + dma_addr_t dma_addr __packed __aligned(sizeof(void *)); and I see pahole, at least sees this correctly: struct { long unsigned int _page_pool_pad; /* 4 4 */ dma_addr_t dma_addr __attribute__((__aligned__(4))); /* 8 8 */ } __attribute__((__packed__)) __attribute__((__aligned__(4))); This presumably affects any 32-bit architecture with a 64-bit phys_addr_t / dma_addr_t. Advice, please? _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel From mboxrd@z Thu Jan 1 00:00:00 1970 Content-Type: multipart/mixed; boundary="===============4604858040857241758==" MIME-Version: 1.0 From: Matthew Wilcox To: kbuild-all@lists.01.org Subject: Bogus struct page layout on 32-bit Date: Sat, 10 Apr 2021 03:43:13 +0100 Message-ID: <20210410024313.GX2531743@casper.infradead.org> In-Reply-To: <202104100656.N7EVvkNZ-lkp@intel.com> List-Id: --===============4604858040857241758== Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable On Sat, Apr 10, 2021 at 06:45:35AM +0800, kernel test robot wrote: > >> include/linux/mm_types.h:274:1: error: static_assert failed due to req= uirement '__builtin_offsetof(struct page, lru) =3D=3D __builtin_offsetof(st= ruct folio, lru)' "offsetof(struct page, lru) =3D=3D offsetof(struct folio,= lru)" > FOLIO_MATCH(lru, lru); > include/linux/mm_types.h:272:2: note: expanded from macro 'FOLIO_MATCH' > static_assert(offsetof(struct page, pg) =3D=3D offsetof(struct= folio, fl)) Well, this is interesting. pahole reports: struct page { long unsigned int flags; /* 0 4 */ /* XXX 4 bytes hole, try to pack */ union { struct { struct list_head lru; /* 8 8 */ ... struct folio { union { struct { long unsigned int flags; /* 0 4 */ struct list_head lru; /* 4 8 */ so this assert has absolutely done its job. But why has this assert triggered? Why is struct page layout not what we thought it was? Turns out it's the dma_addr added in 2019 by commit c25fff7171be ("mm: add dma_addr_t to struct page"). On this particular config, it's 64-bit, and ppc32 requires alignment to 64-bit. So the whole union gets moved out by 4 bytes. Unfortunately, we can't just fix this by putting an 'unsigned long pad' in front of it. It still aligns the entire union to 8 bytes, and then it skips another 4 bytes after the pad. We can fix it like this ... +++ b/include/linux/mm_types.h @@ -96,11 +96,12 @@ struct page { unsigned long private; }; struct { /* page_pool used by netstack */ + unsigned long _page_pool_pad; /** * @dma_addr: might require a 64-bit value even on * 32-bit architectures. */ - dma_addr_t dma_addr; + dma_addr_t dma_addr __packed; }; struct { /* slab, slob and slub */ union { but I don't know if GCC is smart enough to realise that dma_addr is now on an 8 byte boundary and it can use a normal instruction to access it, or whether it'll do something daft like use byte loads to access it. We could also do: + dma_addr_t dma_addr __packed __aligned(sizeof(void = *)); and I see pahole, at least sees this correctly: struct { long unsigned int _page_pool_pad; /* 4 4 */ dma_addr_t dma_addr __attribute__((__aligned__(4)))= ; /* 8 8 */ } __attribute__((__packed__)) __attribute__((__aligned__(4)= )); = This presumably affects any 32-bit architecture with a 64-bit phys_addr_t / dma_addr_t. Advice, please? --===============4604858040857241758==--