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Tue, 29 Jul 2025 09:04:25 +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 09:04:23 +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 6.1.y] mm: khugepaged: fix call hpage_collapse_scan_file() for anonymous vma Date: Tue, 29 Jul 2025 09:04:20 +0000 Message-ID: <20250729090420.19726-1-acsjakub@amazon.de> X-Mailer: git-send-email 2.47.3 MIME-Version: 1.0 X-Originating-IP: [172.19.75.107] X-ClientProxiedBy: EX19D032UWB003.ant.amazon.com (10.13.139.165) To EX19D001UWA001.ant.amazon.com (10.13.138.214) Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 51A5420004 X-Stat-Signature: qf8uej86dsegxm1esr1jhghw5dzrg8mi X-HE-Tag: 1753779870-90860 X-HE-Meta: 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 xoCfHBUr 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 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: List-Subscribe: List-Unsubscribe: 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