From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp-fw-52005.amazon.com (smtp-fw-52005.amazon.com [52.119.213.156]) (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 6A73921D5BE for ; Tue, 29 Jul 2025 09:04:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=52.119.213.156 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753779855; cv=none; b=mNUtV16ZRLLh4vrRgK8/X/ixB9qfvR02DlhFabflilKBVb5Xj8TFe5D7PcKFWykqxzKiap1vXqv+p989M4YtDZ2d5nsQr8mR0r4WnMYQuV1vkYJ7M8P70PFADnEgYGxt6AupYOAjZUxop7y4edHjXhh1d36tx2GDE9UjMijlgmA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753779855; c=relaxed/simple; bh=c7tjMtrSTWUIXrelpaCFueSzC5AyJxqEIC23gTZyDjY=; h=From:To:CC:Subject:Date:Message-ID:MIME-Version:Content-Type; b=HWE3ONAr7PsjWsZcaEysxOqh76oAo+TzMSeZHWoYK29dLnk4tnXkebjpwVuZ+HlEXGTEulkU0k32ZRTAnbAZqbgERjsRGAcrL8QuAdbEuSm4cNI3my6YOGxe8H6ZJ2+dTMF6GmBQWhFaZiVH4S2CoEcCHLPxtg2AK0wJtBcX5pA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amazon.de; spf=pass smtp.mailfrom=amazon.de; dkim=pass (2048-bit key) header.d=amazon.de header.i=@amazon.de header.b=UDXEb1UI; arc=none smtp.client-ip=52.119.213.156 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amazon.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=amazon.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=amazon.de header.i=@amazon.de header.b="UDXEb1UI" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.de; i=@amazon.de; q=dns/txt; s=amazoncorp2; t=1753779854; x=1785315854; h=from:to:cc:subject:date:message-id:mime-version: content-transfer-encoding; bh=q3h1jVcZkOPlZ9Iqdiufq8QHLDIRYxNPqMVEVVeO8BM=; b=UDXEb1UI2/gb6YJfITymyydJ0F/HHBk7091dCexxyALZ1O8PaYwCWdTp +Vmnm6Proqq3iQvhRjTdWAhHxeSQzUo/iPVanAP8MCUq3YycdClH+gJve kihXvuFQlW/8znNjlHQXMWF5IxwS+S2qKwYHXCXg8nuoRZRahuZeuCqtI y2phDmTjlQSaJ6kHBhjCattU5AiFSHxJ6eMfV8S0TCrRgd1TMMfSpNaKV I2tFUCRe38M/qEfDOmPV9svuj0OmB1i59yRgSw32gZjLimtfiqbsrU/Eq xbPZP5pRx200Hjd1ykGfDcMdnJ5DelwOjaLn9v+gC/hNyedFdU1pBuH+V Q==; X-IronPort-AV: E=Sophos;i="6.16,348,1744070400"; d="scan'208";a="766742606" Received: from iad12-co-svc-p1-lb1-vlan3.amazon.com (HELO smtpout.prod.us-west-2.prod.farcaster.email.amazon.dev) ([10.43.8.6]) by smtp-border-fw-52005.iad7.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Jul 2025 09:04:09 +0000 Received: from EX19MTAUWB002.ant.amazon.com [10.0.38.20:59488] by smtpin.naws.us-west-2.prod.farcaster.email.amazon.dev [10.0.52.124:2525] with esmtp (Farcaster) id 92270030-f242-4756-a15e-c972c16f08fb; Tue, 29 Jul 2025 09:04:08 +0000 (UTC) X-Farcaster-Flow-ID: 92270030-f242-4756-a15e-c972c16f08fb Received: from EX19D001UWA001.ant.amazon.com (10.13.138.214) by EX19MTAUWB002.ant.amazon.com (10.250.64.231) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.1544.14; Tue, 29 Jul 2025 09:04:07 +0000 Received: from dev-dsk-acsjakub-1b-6f9934e2.eu-west-1.amazon.com (172.19.75.107) by EX19D001UWA001.ant.amazon.com (10.13.138.214) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.1544.14; Tue, 29 Jul 2025 09:04:05 +0000 From: Jakub Acs To: CC: , , Liu Shixin , Yang Shi , "David Hildenbrand" , Chengming Zhou , Johannes Weiner , Kefeng Wang , Mattew Wilcox , "Muchun Song" , Nanyong Sun , Qi Zheng , Andrew Morton , Subject: [PATCH 6.6.y] mm: khugepaged: fix call hpage_collapse_scan_file() for anonymous vma Date: Tue, 29 Jul 2025 09:04:01 +0000 Message-ID: <20250729090401.18684-1-acsjakub@amazon.de> X-Mailer: git-send-email 2.47.3 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-ClientProxiedBy: EX19D031UWC003.ant.amazon.com (10.13.139.252) To EX19D001UWA001.ant.amazon.com (10.13.138.214) Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit From: Liu Shixin commit f1897f2f08b28ae59476d8b73374b08f856973af upstream. syzkaller reported such a BUG_ON(): ------------[ cut here ]------------ kernel BUG at mm/khugepaged.c:1835! Internal error: Oops - BUG: 00000000f2000800 [#1] SMP ... CPU: 6 UID: 0 PID: 8009 Comm: syz.15.106 Kdump: loaded Tainted: G W 6.13.0-rc6 #22 Tainted: [W]=WARN Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015 pstate: 00400005 (nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : collapse_file+0xa44/0x1400 lr : collapse_file+0x88/0x1400 sp : ffff80008afe3a60 ... Call trace: collapse_file+0xa44/0x1400 (P) hpage_collapse_scan_file+0x278/0x400 madvise_collapse+0x1bc/0x678 madvise_vma_behavior+0x32c/0x448 madvise_walk_vmas.constprop.0+0xbc/0x140 do_madvise.part.0+0xdc/0x2c8 __arm64_sys_madvise+0x68/0x88 invoke_syscall+0x50/0x120 el0_svc_common.constprop.0+0xc8/0xf0 do_el0_svc+0x24/0x38 el0_svc+0x34/0x128 el0t_64_sync_handler+0xc8/0xd0 el0t_64_sync+0x190/0x198 This indicates that the pgoff is unaligned. After analysis, I confirm the vma is mapped to /dev/zero. Such a vma certainly has vm_file, but it is set to anonymous by mmap_zero(). So even if it's mmapped by 2m-unaligned, it can pass the check in thp_vma_allowable_order() as it is an anonymous-mmap, but then be collapsed as a file-mmap. It seems the problem has existed for a long time, but actually, since we have khugepaged_max_ptes_none check before, we will skip collapse it as it is /dev/zero and so has no present page. But commit d8ea7cc8547c limit the check for only khugepaged, so the BUG_ON() can be triggered by madvise_collapse(). Add vma_is_anonymous() check to make such vma be processed by hpage_collapse_scan_pmd(). Link: https://lkml.kernel.org/r/20250111034511.2223353-1-liushixin2@huawei.com Fixes: d8ea7cc8547c ("mm/khugepaged: add flag to predicate khugepaged-only behavior") Signed-off-by: Liu Shixin Reviewed-by: Yang Shi Acked-by: David Hildenbrand Cc: Chengming Zhou Cc: Johannes Weiner Cc: Kefeng Wang Cc: Mattew Wilcox Cc: Muchun Song Cc: Nanyong Sun Cc: Qi Zheng Signed-off-by: Andrew Morton [acsjakub: backport, clean apply] Cc: Jakub Acs Cc: linux-mm@kvack.org --- Ran into the crash with syzkaller, backporting this patch works - the reproducer no longer crashes. Please let me know if there was a reason not to backport. mm/khugepaged.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index b538c3d48386..abd5764e4864 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -2404,7 +2404,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result, VM_BUG_ON(khugepaged_scan.address < hstart || khugepaged_scan.address + HPAGE_PMD_SIZE > hend); - if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) { + if (IS_ENABLED(CONFIG_SHMEM) && !vma_is_anonymous(vma)) { struct file *file = get_file(vma->vm_file); pgoff_t pgoff = linear_page_index(vma, khugepaged_scan.address); @@ -2750,7 +2750,7 @@ int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev, mmap_assert_locked(mm); memset(cc->node_load, 0, sizeof(cc->node_load)); nodes_clear(cc->alloc_nmask); - if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) { + if (IS_ENABLED(CONFIG_SHMEM) && !vma_is_anonymous(vma)) { struct file *file = get_file(vma->vm_file); pgoff_t pgoff = linear_page_index(vma, addr); -- 2.47.3 Amazon Web Services Development Center Germany GmbH Tamara-Danz-Str. 13 10243 Berlin Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss Eingetragen am Amtsgericht Charlottenburg unter HRB 257764 B Sitz: Berlin Ust-ID: DE 365 538 597