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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 36C06C433FE for ; Thu, 13 Jan 2022 10:10:37 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 9A5946B00AB; Thu, 13 Jan 2022 05:10:36 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 954086B00AD; Thu, 13 Jan 2022 05:10:36 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 81BDB6B00AE; Thu, 13 Jan 2022 05:10:36 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0116.hostedemail.com [216.40.44.116]) by kanga.kvack.org (Postfix) with ESMTP id 752876B00AB for ; Thu, 13 Jan 2022 05:10:36 -0500 (EST) Received: from smtpin05.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 2C0FC181CB2C6 for ; Thu, 13 Jan 2022 10:10:36 +0000 (UTC) X-FDA: 79024844472.05.7D4F65B Received: from mail-lf1-f48.google.com (mail-lf1-f48.google.com [209.85.167.48]) by imf26.hostedemail.com (Postfix) with ESMTP id A3317140002 for ; Thu, 13 Jan 2022 10:10:35 +0000 (UTC) Received: by mail-lf1-f48.google.com with SMTP id br17so17680320lfb.6 for ; Thu, 13 Jan 2022 02:10:35 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=RadJqXCNgJSuxrAQxYqXMQELWeTlrMxxcxtdQOTtr8I=; b=KOvWWdg4A6g44OmDCoCZvBPZQEI06nFjYj0Pw7ezvtKVkrF/I1gr5ijlDWIufHUr2v LH2Ehr3FvEMxB55ftrqKAiSs2ncdLIO3FRGyCoNnpE6D8CpD3Wa4aan01lDy7AC214Vm pZyet1QGfcz9b6tgyiWBMy15Q2n38nRXJYjZpRuYQfln/gieeGCzhaAvi0Vwmn5tOY1N N/hmtiy4BNsqVvpUMoyV+K+AOAv4Fn6Gy6p6Me/PEv4bPJWOjVJdwj71FKcpJ/T1y6Ii schqddqevKrc8eZiZAR93pqgVxItnyfWhPQnK7t/FIbLY78oJEWdg0HLh3fonHFMBpu6 sVYQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=RadJqXCNgJSuxrAQxYqXMQELWeTlrMxxcxtdQOTtr8I=; b=MGyseh9QrV7p+9yIz7aBjPl3SwBGJe70MgynFxfrE5ry3E4sL6YkV6r7qDvaYz90VM wHo1UH62V6SEPuQJSQ7BWWiCZ1bHSvdT2q+Uh10j4w1qL5nGHDCx2iveOtrOi1H/7dYU 7QguM3pJmXGiqE1Eo3O6GWITMfwqbMzMD9m9Y5M/WA7EsM+lIT7f9qAJUbY96TxtCrIy l9OAMXJEvAyX+k2YnTyrNEtAJLxc1nuSPjraT7dUG/LU1tXMtReqN6ayw6R/+k8e+pRr 549LScJIP7WmzFUZvLvqLvwvjvgs9gWJCutj3bRM1nfxzGegQhWXKNRSPOqoxKtdjsUP dhzA== X-Gm-Message-State: AOAM531fF8UNCWQrpTYUqVcXZH6pghhvsiJXhelQzt9DKU+YTvYpFoE/ 4v7DaqWJU6YASD7CXyfnuvy805sFNGRanuUyP+UpFw== X-Google-Smtp-Source: ABdhPJwh+EyRBzFDdoNIF6CuwmhbkxgFXBjne0410iYswXwVmwIk0qa395loxmGEQ4bdDlanGDsU9P7A1mHz/x422Ng= X-Received: by 2002:a2e:8751:: with SMTP id q17mr920669ljj.235.1642068632823; Thu, 13 Jan 2022 02:10:32 -0800 (PST) MIME-Version: 1.0 References: <20220112215625.4144871-1-shy828301@gmail.com> In-Reply-To: <20220112215625.4144871-1-shy828301@gmail.com> From: Jann Horn Date: Thu, 13 Jan 2022 11:10:04 +0100 Message-ID: Subject: Re: [PATCH] fs/proc: task_mmu.c: don't read mapcount for migration entry To: Yang Shi Cc: kirill.shutemov@linux.intel.com, willy@infradead.org, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=KOvWWdg4; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf26.hostedemail.com: domain of jannh@google.com designates 209.85.167.48 as permitted sender) smtp.mailfrom=jannh@google.com X-Stat-Signature: xiefyfb9dc3kxfg33nrmjtwr94h8skpe X-Rspamd-Queue-Id: A3317140002 X-Rspamd-Server: rspam12 X-HE-Tag: 1642068635-33699 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Jan 12, 2022 at 10:56 PM Yang Shi wrote: > The syzbot reported the below BUG: > > kernel BUG at include/linux/page-flags.h:785! > invalid opcode: 0000 [#1] PREEMPT SMP KASAN > CPU: 1 PID: 4392 Comm: syz-executor560 Not tainted 5.16.0-rc6-syzkaller #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > RIP: 0010:PageDoubleMap include/linux/page-flags.h:785 [inline] > RIP: 0010:__page_mapcount+0x2d2/0x350 mm/util.c:744 > Code: e8 d3 16 d1 ff 48 c7 c6 c0 00 b6 89 48 89 ef e8 94 4e 04 00 0f 0b e8 bd 16 d1 ff 48 c7 c6 60 01 b6 89 48 89 ef e8 7e 4e 04 00 <0f> 0b e8 a7 16 d1 ff 48 c7 c6 a0 01 b6 89 4c 89 f7 e8 68 4e 04 00 > RSP: 0018:ffffc90002b6f7b8 EFLAGS: 00010293 > RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 > RDX: ffff888019619d00 RSI: ffffffff81a68c12 RDI: 0000000000000003 > RBP: ffffea0001bdc2c0 R08: 0000000000000029 R09: 00000000ffffffff > R10: ffffffff8903e29f R11: 00000000ffffffff R12: 00000000ffffffff > R13: 00000000ffffea00 R14: ffffc90002b6fb30 R15: ffffea0001bd8001 > FS: 00007faa2aefd700(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007fff7e663318 CR3: 0000000018c6e000 CR4: 00000000003506e0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > Call Trace: > > page_mapcount include/linux/mm.h:837 [inline] > smaps_account+0x470/0xb10 fs/proc/task_mmu.c:466 > smaps_pte_entry fs/proc/task_mmu.c:538 [inline] > smaps_pte_range+0x611/0x1250 fs/proc/task_mmu.c:601 > walk_pmd_range mm/pagewalk.c:128 [inline] > walk_pud_range mm/pagewalk.c:205 [inline] > walk_p4d_range mm/pagewalk.c:240 [inline] > walk_pgd_range mm/pagewalk.c:277 [inline] > __walk_page_range+0xe23/0x1ea0 mm/pagewalk.c:379 > walk_page_vma+0x277/0x350 mm/pagewalk.c:530 > smap_gather_stats.part.0+0x148/0x260 fs/proc/task_mmu.c:768 > smap_gather_stats fs/proc/task_mmu.c:741 [inline] > show_smap+0xc6/0x440 fs/proc/task_mmu.c:822 > seq_read_iter+0xbb0/0x1240 fs/seq_file.c:272 > seq_read+0x3e0/0x5b0 fs/seq_file.c:162 > vfs_read+0x1b5/0x600 fs/read_write.c:479 > ksys_read+0x12d/0x250 fs/read_write.c:619 > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 > entry_SYSCALL_64_after_hwframe+0x44/0xae > RIP: 0033:0x7faa2af6c969 > Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 11 15 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48 > RSP: 002b:00007faa2aefd288 EFLAGS: 00000246 ORIG_RAX: 0000000000000000 > RAX: ffffffffffffffda RBX: 00007faa2aff4418 RCX: 00007faa2af6c969 > RDX: 0000000000002025 RSI: 0000000020000100 RDI: 0000000000000003 > RBP: 00007faa2aff4410 R08: 00007faa2aefd700 R09: 0000000000000000 > R10: 00007faa2aefd700 R11: 0000000000000246 R12: 00007faa2afc20ac > R13: 00007fff7e6632bf R14: 00007faa2aefd400 R15: 0000000000022000 > > Modules linked in: > ---[ end trace 24ec93ff95e4ac3d ]--- > RIP: 0010:PageDoubleMap include/linux/page-flags.h:785 [inline] > RIP: 0010:__page_mapcount+0x2d2/0x350 mm/util.c:744 > Code: e8 d3 16 d1 ff 48 c7 c6 c0 00 b6 89 48 89 ef e8 94 4e 04 00 0f 0b e8 bd 16 d1 ff 48 c7 c6 60 01 b6 89 48 89 ef e8 7e 4e 04 00 <0f> 0b e8 a7 16 d1 ff 48 c7 c6 a0 01 b6 89 4c 89 f7 e8 68 4e 04 00 > RSP: 0018:ffffc90002b6f7b8 EFLAGS: 00010293 > RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 > RDX: ffff888019619d00 RSI: ffffffff81a68c12 RDI: 0000000000000003 > RBP: ffffea0001bdc2c0 R08: 0000000000000029 R09: 00000000ffffffff > R10: ffffffff8903e29f R11: 00000000ffffffff R12: 00000000ffffffff > R13: 00000000ffffea00 R14: ffffc90002b6fb30 R15: ffffea0001bd8001 > FS: 00007faa2aefd700(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007fff7e663318 CR3: 0000000018c6e000 CR4: 00000000003506e0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > > The reproducer was trying to reading /proc/$PID/smaps when calling > MADV_FREE at the mean time. MADV_FREE may split THPs if it is called > for partial THP. It may trigger the below race: > > CPU A CPU B > ----- ----- > smaps walk: MADV_FREE: > page_mapcount() > PageCompound() > split_huge_page() > page = compound_head(page) > PageDoubleMap(page) > > When calling PageDoubleMap() this page is not a tail page of THP anymore > so the BUG is triggered. > > This could be fixed by elevated refcount of the page before calling > mapcount, but it prevents from counting migration entries, and it seems > overkilling because the race just could happen when PMD is split so all > PTE entries of tail pages are actually migration entries, and > smaps_account() does treat migration entries as mapcount == 1 as Kirill > pointed out. > > Add a new parameter for smaps_account() to tell this entry is migration > entry then skip calling page_mapcount(). Don't skip getting mapcount for > device private entries since they do track references with mapcount. > > Reported-by: syzbot+1f52b3a18d5633fa7f82@syzkaller.appspotmail.com maybe add: Fixes: b1d4d9e0cbd0 ("proc/smaps: carefully handle migration entries") > Cc: "Kirill A. Shutemov" > Cc: Jann Horn > Cc: Matthew Wilcox > Cc: > Signed-off-by: Yang Shi