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 ADF9DC433B4 for ; Sat, 10 Apr 2021 14:08:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 860DF60FF0 for ; Sat, 10 Apr 2021 14:08:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234569AbhDJOI0 (ORCPT ); Sat, 10 Apr 2021 10:08:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51932 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234536AbhDJOIY (ORCPT ); Sat, 10 Apr 2021 10:08:24 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3EC88C06138A; Sat, 10 Apr 2021 07:08:10 -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=RTtiSoWYCZ04uVGpMhjmbWk2I8ENKaw5/2meK4GSvVY=; b=Ukx/6bcpMFZOkdXU+6AgH4koIC JYQO1FzV6/eHzojqXmXhQ/Z2nX30bYjwSNpUwoyoumWWCurMZmGxnEEecD4PaJKmp4GXz6p1b2+/q 0RMOdRNqSOTRFvUwSPVFDwmRSjjZ3ITuDSJ2aLHHPe64xqcxY+ZqKMubFJS1QJtFXq4Kxm3hnd3of BUO/DXOBYmNDLsQ1dD5dC1DSv1nb1TAKfNZI+Mr+uPZqIQ8bzPe8DP+78gLma/EybXZRgoiB8h8sl A7MmK5nSVyMIc1DrKxYN/Zbg0WVr4tZgOm6InniGGemi70dpNNfZB+gF4ZdfcKuxzTQhjyUXVU1QB g8Q5EMEA==; Received: from willy by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1lVEGC-001lqY-BT; Sat, 10 Apr 2021 14:07:08 +0000 Date: Sat, 10 Apr 2021 15:06:52 +0100 From: Matthew Wilcox To: Ilias Apalodimas Cc: Jesper Dangaard Brouer , kernel test robot , Linux-MM , kbuild-all@lists.01.org, clang-built-linux@googlegroups.com, open list , linux-fsdevel@vger.kernel.org, Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , linuxppc-dev@lists.ozlabs.org, Linux ARM , "David S. Miller" , Ivan Khoronzhuk , Matteo Croce , "netdev@vger.kernel.org" , Grygorii Strashko Subject: Re: Bogus struct page layout on 32-bit Message-ID: <20210410140652.GY2531743@casper.infradead.org> References: <20210409185105.188284-3-willy@infradead.org> <202104100656.N7EVvkNZ-lkp@intel.com> <20210410024313.GX2531743@casper.infradead.org> <20210410082158.79ad09a6@carbon> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org How about moving the flags into the union? A bit messy, but we don't have to play games with __packed__. diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 1210a8e41fad..f374d2f06255 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -68,16 +68,22 @@ struct mem_cgroup; #endif struct page { - unsigned long flags; /* Atomic flags, some possibly - * updated asynchronously */ /* - * Five words (20/40 bytes) are available in this union. - * WARNING: bit 0 of the first word is used for PageTail(). That - * means the other users of this union MUST NOT use the bit to + * This union is six words (24 / 48 bytes) in size. + * The first word is reserved for atomic flags, often updated + * asynchronously. Use the PageFoo() macros to access it. Some + * of the flags can be reused for your own purposes, but the + * word as a whole often contains other information and overwriting + * it will cause functions like page_zone() and page_node() to stop + * working correctly. + * + * Bit 0 of the second word is used for PageTail(). That + * means the other users of this union MUST leave the bit zero to * avoid collision and false-positive PageTail(). */ union { struct { /* Page cache and anonymous pages */ + unsigned long flags; /** * @lru: Pageout list, eg. active_list protected by * lruvec->lru_lock. Sometimes used as a generic list @@ -96,6 +102,8 @@ struct page { unsigned long private; }; struct { /* page_pool used by netstack */ + unsigned long _pp_flags; + unsigned long _pp_pad; /** * @dma_addr: might require a 64-bit value even on * 32-bit architectures. @@ -103,6 +111,7 @@ struct page { dma_addr_t dma_addr; }; struct { /* slab, slob and slub */ + unsigned long _slab_flags; union { struct list_head slab_list; struct { /* Partial pages */ @@ -130,6 +139,7 @@ struct page { }; }; struct { /* Tail pages of compound page */ + unsigned long _tail1_flags; unsigned long compound_head; /* Bit zero is set */ /* First tail page only */ @@ -139,12 +149,14 @@ struct page { unsigned int compound_nr; /* 1 << compound_order */ }; struct { /* Second tail page of compound page */ + unsigned long _tail2_flags; unsigned long _compound_pad_1; /* compound_head */ atomic_t hpage_pinned_refcount; /* For both global and memcg */ struct list_head deferred_list; }; struct { /* Page table pages */ + unsigned long _pt_flags; unsigned long _pt_pad_1; /* compound_head */ pgtable_t pmd_huge_pte; /* protected by page->ptl */ unsigned long _pt_pad_2; /* mapping */ @@ -159,6 +171,7 @@ struct page { #endif }; struct { /* ZONE_DEVICE pages */ + unsigned long _zd_flags; /** @pgmap: Points to the hosting device page map. */ struct dev_pagemap *pgmap; void *zone_device_data; @@ -174,8 +187,11 @@ struct page { */ }; - /** @rcu_head: You can use this to free a page by RCU. */ - struct rcu_head rcu_head; + struct { + unsigned long _rcu_flags; + /** @rcu_head: You can use this to free a page by RCU. */ + struct rcu_head rcu_head; + }; }; union { /* This union is 4 bytes in size. */