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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 042A9C433F5 for ; Thu, 13 Jan 2022 19:02:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237819AbiAMTCb (ORCPT ); Thu, 13 Jan 2022 14:02:31 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42240 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237805AbiAMTCV (ORCPT ); Thu, 13 Jan 2022 14:02:21 -0500 Received: from mail-ed1-x535.google.com (mail-ed1-x535.google.com [IPv6:2a00:1450:4864:20::535]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8740EC06161C; Thu, 13 Jan 2022 11:02:20 -0800 (PST) Received: by mail-ed1-x535.google.com with SMTP id w16so26610627edc.11; Thu, 13 Jan 2022 11:02:20 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=BYuO2RToGrqH8LgFfhvjBYsbSoicgjpkDp2gRNvqWQY=; b=DZ/kbWgGMCTHV+uHtOVk0+tROYcfvDCgCOtrieSG8Ny8eX5ZPA1/remMhqbVrXcPGk uXPygKvZIuTlj/52UHMLFqG0+LzYpt4jOyagC8NNAlQlE2DChbTYwpWyHXmuhgAhnyb3 IPqIApubpmJhFsp2RIZsHVLgqiXdvUQbwPtpoEqer4yIfcjgEmHh+RDukAHuBbSaK7JX M0gqTGI+BRSdf/m1kDhWI/n3i/loiNxiIdKejxBtUE10gK6KiuRtumREUnT4jPyGoATZ Ra5oNtcki7J4ERsAC2YRNAUNYCWfZajR4fTKlORkWmPGkerwlJlgPCs42UiBbOXC6Kpl MisQ== 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=BYuO2RToGrqH8LgFfhvjBYsbSoicgjpkDp2gRNvqWQY=; b=S+Ygm3ufdzrAeLZvuwOL2bYX9tYpzCgsOJWjsQdnQgdTp8vesXU1dMs6GpjvOkxucM KfKZ1oz9d1YTv0wbmReLeaFbKU3mBO3UmOOwihkXQqm16zIczzIZsn26rd+tAFUxD9Td pK4cq5/EOfyeWDdN1ZxLQiARQ9QAvwfMkhdV3MG6Nc7aM82KmTD9YV4l+t8VnzaZkhm6 Y1GChjGwPR3d5ojWYDdSHyuBScCEuweZXqMjl0BrMbuS8z+OWq8lw2q/GJRkUtM0qJbF dgfiGL/DzK/f5lQNYf4nf3gNw4vq9J5/EHoWDhfFYnkgRBvt+VAjD31VUF0gdK1EMj2z bMtA== X-Gm-Message-State: AOAM5319i/e9Ux9+NFbSvFUKJ9kpPEwKCIyW2llbXHGmT1XNmaUxq3QP Vef7BvuVYwQxNO/iGu15DDdMsEUiJquszU43a7g= X-Google-Smtp-Source: ABdhPJz+GwLUrKvddOdQvVc3w8lNqKV1TIumclPWYxvOpP6lr10DXXA80B+w1hRkNtLCBFLOIzskrax6dHUBXGApSN0= X-Received: by 2002:a17:906:f251:: with SMTP id gy17mr4787717ejb.377.1642100539082; Thu, 13 Jan 2022 11:02:19 -0800 (PST) MIME-Version: 1.0 References: <20220112215625.4144871-1-shy828301@gmail.com> In-Reply-To: From: Yang Shi Date: Thu, 13 Jan 2022 11:02:06 -0800 Message-ID: Subject: Re: [PATCH] fs/proc: task_mmu.c: don't read mapcount for migration entry To: Jann Horn Cc: "Kirill A. Shutemov" , Matthew Wilcox , Andrew Morton , Linux MM , Linux Kernel Mailing List , stable Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 13, 2022 at 2:10 AM Jann Horn wrote: > > 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") Yeah, absolutely, thanks for finding the proper fix tag. It is quite an old commit. > > > Cc: "Kirill A. Shutemov" > > Cc: Jann Horn > > Cc: Matthew Wilcox > > Cc: > > Signed-off-by: Yang Shi