From nobody Tue Nov 26 04:36:10 2024 Received: from out-183.mta1.migadu.com (out-183.mta1.migadu.com [95.215.58.183]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 483CD1CBEBC for ; Mon, 21 Oct 2024 17:35:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.183 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729532123; cv=none; b=fBgJjtluW2J6BnYaXKg26UD9ekExFJmV0PmfMonyJ++VdyNR49EAn5ftTHJH/6XkL39Mala272imzV4ugYRRPKZZUXKf0dgwg38toj3PDeoaxib+xBn+DzhB7Hd4PMSwo5GXfktof0vOmO5/O5bYoBo7pVm0a+0b++8X/24F5xE= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729532123; c=relaxed/simple; bh=czQ9g0mFdvgWl9O8XJj/3MVzvE7/qQBGFDMz0c7CFFQ=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=AnNtom1xURnOUkC24lr3HA4NcbUY/4tA3yKLEheYykX2dQoFUAwkIlcyWYxhKBRBa/QTrLbJCQOyQKWMZ/uUGtdxOA0CFsx5dn5NeMa3jYJwydJonuMtk/tfx5qCLsz5JNeGEnr3gztKqjCVp/Y9QZVcLGkjgxYR00ZGK7CgWDM= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=nTb8Qi6P; arc=none smtp.client-ip=95.215.58.183 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="nTb8Qi6P" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1729532116; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=ng2+tosjoBBu6IdGY0OAnCymCQLdInYE8eT0ciVoT6Q=; b=nTb8Qi6PWoiuOxAhB2TmVQyT041O2AFkafYBMJopBHfQOCTheY74oOCMxNH5WXHJi6XH8S wH1DrvZ7kX9K0x0Eyig4ZzFCWHsTH/Nodj4ftVlvHF7qEkNZtJA4itciPtPuj65L6Fc3N6 aWIQ45xJ+gwJ3pbUhozwlm9h9TgMHBk= From: Roman Gushchin To: Andrew Morton Cc: linux-mm@kvack.org, Vlastimil Babka , linux-kernel@vger.kernel.org, Roman Gushchin , stable@vger.kernel.org, Hugh Dickins , Matthew Wilcox Subject: [PATCH v2] mm: page_alloc: move mlocked flag clearance into free_pages_prepare() Date: Mon, 21 Oct 2024 17:34:55 +0000 Message-ID: <20241021173455.2691973-1-roman.gushchin@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset="utf-8" Syzbot reported a bad page state problem caused by a page being freed using free_page() still having a mlocked flag at free_pages_prepare() stage: BUG: Bad page state in process syz.0.15 pfn:1137bb page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff8881137b= b870 pfn:0x1137bb flags: 0x400000000080000(mlocked|node=3D0|zone=3D1) raw: 0400000000080000 0000000000000000 dead000000000122 0000000000000000 raw: ffff8881137bb870 0000000000000000 00000000ffffffff 0000000000000000 page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set page_owner tracks the page as allocated page last allocated via order 0, migratetype Unmovable, gfp_mask 0x400dc0(GFP_KERNEL_ACCOUNT|__GFP_ZERO), pid 3005, tgid 3004 (syz.0.15), ts 61546 608067, free_ts 61390082085 set_page_owner include/linux/page_owner.h:32 [inline] post_alloc_hook+0x1f3/0x230 mm/page_alloc.c:1537 prep_new_page mm/page_alloc.c:1545 [inline] get_page_from_freelist+0x3008/0x31f0 mm/page_alloc.c:3457 __alloc_pages_noprof+0x292/0x7b0 mm/page_alloc.c:4733 alloc_pages_mpol_noprof+0x3e8/0x630 mm/mempolicy.c:2265 kvm_coalesced_mmio_init+0x1f/0xf0 virt/kvm/coalesced_mmio.c:99 kvm_create_vm virt/kvm/kvm_main.c:1235 [inline] kvm_dev_ioctl_create_vm virt/kvm/kvm_main.c:5500 [inline] kvm_dev_ioctl+0x13bb/0x2320 virt/kvm/kvm_main.c:5542 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:907 [inline] __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:893 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0x69/0x110 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x76/0x7e page last free pid 951 tgid 951 stack trace: reset_page_owner include/linux/page_owner.h:25 [inline] free_pages_prepare mm/page_alloc.c:1108 [inline] free_unref_page+0xcb1/0xf00 mm/page_alloc.c:2638 vfree+0x181/0x2e0 mm/vmalloc.c:3361 delayed_vfree_work+0x56/0x80 mm/vmalloc.c:3282 process_one_work kernel/workqueue.c:3229 [inline] process_scheduled_works+0xa5c/0x17a0 kernel/workqueue.c:3310 worker_thread+0xa2b/0xf70 kernel/workqueue.c:3391 kthread+0x2df/0x370 kernel/kthread.c:389 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244 A reproducer is available here: https://syzkaller.appspot.com/x/repro.c?x=3D1437939f980000 The problem was originally introduced by commit b109b87050df ("mm/munlock: replace clear_page_mlock() by final clearance"): it was handling focused on handling pagecache and anonymous memory and wasn't suitable for lower level get_page()/free_page() API's used for example by KVM, as with this reproducer. Fix it by moving the mlocked flag clearance down to free_page_prepare(). The bug itself if fairly old and harmless (aside from generating these warnings). Closes: https://syzkaller.appspot.com/x/report.txt?x=3D169a47d0580000 Fixes: b109b87050df ("mm/munlock: replace clear_page_mlock() by final clear= ance") Signed-off-by: Roman Gushchin Cc: Cc: Hugh Dickins Cc: Matthew Wilcox Cc: Vlastimil Babka Acked-by: Hugh Dickins --- mm/page_alloc.c | 15 +++++++++++++++ mm/swap.c | 14 -------------- 2 files changed, 15 insertions(+), 14 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index bc55d39eb372..7535d78862ab 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1044,6 +1044,7 @@ __always_inline bool free_pages_prepare(struct page *= page, bool skip_kasan_poison =3D should_skip_kasan_poison(page); bool init =3D want_init_on_free(); bool compound =3D PageCompound(page); + struct folio *folio =3D page_folio(page); =20 VM_BUG_ON_PAGE(PageTail(page), page); =20 @@ -1053,6 +1054,20 @@ __always_inline bool free_pages_prepare(struct page = *page, if (memcg_kmem_online() && PageMemcgKmem(page)) __memcg_kmem_uncharge_page(page, order); =20 + /* + * In rare cases, when truncation or holepunching raced with + * munlock after VM_LOCKED was cleared, Mlocked may still be + * found set here. This does not indicate a problem, unless + * "unevictable_pgs_cleared" appears worryingly large. + */ + if (unlikely(folio_test_mlocked(folio))) { + long nr_pages =3D folio_nr_pages(folio); + + __folio_clear_mlocked(folio); + zone_stat_mod_folio(folio, NR_MLOCK, -nr_pages); + count_vm_events(UNEVICTABLE_PGCLEARED, nr_pages); + } + if (unlikely(PageHWPoison(page)) && !order) { /* Do not let hwpoison pages hit pcplists/buddy */ reset_page_owner(page, order); diff --git a/mm/swap.c b/mm/swap.c index 835bdf324b76..7cd0f4719423 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -78,20 +78,6 @@ static void __page_cache_release(struct folio *folio, st= ruct lruvec **lruvecp, lruvec_del_folio(*lruvecp, folio); __folio_clear_lru_flags(folio); } - - /* - * In rare cases, when truncation or holepunching raced with - * munlock after VM_LOCKED was cleared, Mlocked may still be - * found set here. This does not indicate a problem, unless - * "unevictable_pgs_cleared" appears worryingly large. - */ - if (unlikely(folio_test_mlocked(folio))) { - long nr_pages =3D folio_nr_pages(folio); - - __folio_clear_mlocked(folio); - zone_stat_mod_folio(folio, NR_MLOCK, -nr_pages); - count_vm_events(UNEVICTABLE_PGCLEARED, nr_pages); - } } =20 /* --=20 2.47.0.105.g07ac214952-goog