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Wed, 30 Jul 2025 07:39:47 +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 v2 6.12.y] mm: khugepaged: fix call hpage_collapse_scan_file() for anonymous vma Date: Wed, 30 Jul 2025 07:39:45 +0000 Message-ID: <20250730073945.27790-1-acsjakub@amazon.de> X-Mailer: git-send-email 2.47.3 MIME-Version: 1.0 X-Originating-IP: [172.19.75.107] X-ClientProxiedBy: EX19D041UWB001.ant.amazon.com (10.13.139.132) To EX19D001UWA001.ant.amazon.com (10.13.138.214) Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit X-Stat-Signature: fkxmyh8cmkn9x5qc6qsm5t8pzqs4nm89 X-Rspamd-Queue-Id: 13567140009 X-Rspamd-Server: rspam10 X-Rspam-User: X-HE-Tag: 1753861194-596767 X-HE-Meta: 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 8NGGhL2o 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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] Signed-off-by: Jakub Acs Cc: linux-mm@kvack.org --- v1 -> v2: fix missing sign-off 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