Message-ID: <e290b9c3-7bcd-4b6a-9e5f-dc3c7d3d43e4@redhat.com>
Date: Mon, 4 Aug 2025 10:18:28 +0200
From: David Hildenbrand <david@...hat.com>
To: syzbot <syzbot+2a0d2af125c01db73079@...kaller.appspotmail.com>,
 akpm@...ux-foundation.org, almaz.alexandrovich@...agon-software.com,
 apopple@...dia.com, byungchul@...com, gourry@...rry.net,
 joshua.hahnjy@...il.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 matthew.brost@...el.com, ntfs3@...ts.linux.dev, rakie.kim@...com,
 syzkaller-bugs@...glegroups.com, ying.huang@...ux.alibaba.com, ziy@...dia.com
Subject: Re: [syzbot] [mm?] [ntfs3?] kernel BUG in set_page_refcounted

On 01.08.25 19:38, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    260f6f4fda93 Merge tag 'drm-next-2025-07-30' of https://gi..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=15c31834580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=bb7581d3fb1bb0d7
> dashboard link: https://syzkaller.appspot.com/bug?extid=2a0d2af125c01db73079
> compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=149062a2580000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/1fce1d4d56ce/disk-260f6f4f.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/01688cdba884/vmlinux-260f6f4f.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/eba9b2f77e6a/bzImage-260f6f4f.xz
> mounted in repro: https://storage.googleapis.com/syzbot-assets/95ad5335ac08/mount_0.gz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+2a0d2af125c01db73079@...kaller.appspotmail.com
> 
>   do_group_exit+0x21c/0x2d0 kernel/exit.c:1105
>   __do_sys_exit_group kernel/exit.c:1116 [inline]
>   __se_sys_exit_group kernel/exit.c:1114 [inline]
>   __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1114
>   x64_sys_call+0x21f7/0x2200 arch/x86/include/generated/asm/syscalls_64.h:232
>   do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>   do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
>   entry_SYSCALL_64_after_hwframe+0x77/0x7f
> ------------[ cut here ]------------
> kernel BUG at mm/internal.h:491!

	VM_BUG_ON_PAGE(page_ref_count(page), page);

We seem to have page with a non-zero refcount in the buddy.


The Oops below has a VM_BUG_ON_PAGE before it

[  531.894112][ [  531.894112][ T7687] page: refcount:255 mapcount:-255 mapping:0000000000000000 index:0x0 pfn:0x460e7
[  531.894153][ T7687] head: order:0 mapcount:420858112 entire_mapcount:1009385984 nr_pages_mapped:6946817 pincount:-7831513
[  531.894176][ T7687] flags: 0x80000000000000ff(locked|waiters|referenced|uptodate|dirty|lru|writeback|head|node=32|zone=0)
[  531.894219][ T7687] raw: 80000000000000ff 0000000000000000 ad00000000012200 00000000000000de
[  531.894240][ T7687] raw: 0000000000000000 0000000000000000 000000ffffffff00 0000000000000000
[  531.894261][ T7687] head: 80000000000000ff 0000000000000000 ad00000000012200 00000000000000de
[  531.894282][ T7687] head: 0000000000000000 0000000000000000 000000ffffffff00 0000000000000000
[  531.894306][ T7687] head: 8000000002082800 ffea000118504800 ffea00011915c8ff ff8880273c2a01ff
[  531.894327][ T7687] head: 0000000c0089feff 0000000000000000 0000010000000000 ff88801aae000000
[  531.894341][ T7687] page dumped because: VM_BUG_ON_PAGE(page_ref_count(page))
[  531.894363][ T7687] page_owner tracks the page as allocated
[  531.894372][ T7687] page last allocated via order 0, migratetype Movable, gfp_mask 0x140cca(GFP_HIGHUSER_MOVABLE|__GFP_COMP), pid 7405, tgid 7405 (udevd), ts 508249020508, free_ts 508221042792
[  531.894410][ T7687]  post_alloc_hook+0x240/0x2a0
[  531.894458][ T7687]  get_page_from_freelist+0x2119/0x21b0
[  531.894479][ T7687]  __alloc_frozen_pages_noprof+0x181/0x370
[  531.894502][ T7687]  alloc_pages_mpol+0xd1/0x380
[  531.894531][ T7687]  vma_alloc_folio_noprof+0xe4/0x280
[  531.894560][ T7687]  folio_prealloc+0x30/0x180
[  531.894594][ T7687]  do_wp_page+0x11ee/0x4910
[  531.894623][ T7687]  handle_mm_fault+0x97c/0x3400
[  531.894652][ T7687]  do_user_addr_fault+0xa81/0x1390
[  531.894676][ T7687]  exc_page_fault+0x76/0xf0
[  531.894700][ T7687]  asm_exc_page_fault+0x26/0x30
[  531.894722][ T7687] page last free pid 7403 tgid 7403 stack trace:
[  531.894735][ T7687]  free_unref_folios+0xc8b/0x14e0
[  531.894775][ T7687]  folios_put_refs+0x569/0x670
[  531.894811][ T7687]  free_pages_and_swap_cache+0x277/0x520
[  531.894832][ T7687]  tlb_flush_mmu+0x3a0/0x680
[  531.894851][ T7687]  tlb_finish_mmu+0xc3/0x1d0
[  531.894872][ T7687]  exit_mmap+0x44c/0xb50
[  531.894902][ T7687]  __mmput+0xcb/0x3d0
[  531.894924][ T7687]  exit_mm+0x1da/0x2c0
[  531.894954][ T7687]  do_exit+0x648/0x2300
[  531.894986][ T7687]  do_group_exit+0x21c/0x2d0
[  531.895018][ T7687]  __x64_sys_exit_group+0x3f/0x40
[  531.895050][ T7687]  x64_sys_call+0x21f7/0x2200
[  531.895086][ T7687]  do_syscall_64+0xfa/0x3b0
[  531.895114][ T7687]  entry_SYSCALL_64_after_hwframe+0x77/0x7f


Looks quite messy "page_owner tracks the page as allocated" seems to imply that the page is indeed still
allocated.

> Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
> CPU: 1 UID: 0 PID: 7687 Comm: syz.0.738 Tainted: G        W           6.16.0-syzkaller-08685-g260f6f4fda93 #0 PREEMPT_{RT,(full)}
> Tainted: [W]=WARN
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
> RIP: 0010:set_page_refcounted+0x142/0x1e0 mm/internal.h:491
> Code: 48 89 d8 48 25 ff 0f 00 00 74 21 e8 18 4e a4 ff e9 2c ff ff ff e8 0e 4e a4 ff 48 89 df 48 c7 c6 a0 47 17 8b e8 4f 05 e9 ff 90 <0f> 0b 48 89 df be 08 00 00 00 e8 3f 27 03 00 48 89 d8 48 c1 e8 03
> RSP: 0018:ffffc900065f7670 EFLAGS: 00010246
> RAX: 0ebb44fe4874cf00 RBX: ffffea00011839ff RCX: 0ebb44fe4874cf00
> RDX: 0000000000000001 RSI: ffffffff8d1dbecc RDI: ffff88802f581dc0
> RBP: 00000000000000ff R08: 0000000000000000 R09: 0000000000000000
> R10: dffffc0000000000 R11: ffffed1017124863 R12: 1ffffd4000230746
> R13: 0000000000000000 R14: ffffea0001183a33 R15: dffffc0000000000
> FS:  00007f4368d266c0(0000) GS:ffff888126c1e000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007feecfc73000 CR3: 0000000034c06000 CR4: 00000000003526f0
> Call Trace:
>   <TASK>
>   alloc_pages_noprof+0xe4/0x1e0 mm/mempolicy.c:2513
>   folio_alloc_noprof+0x22/0xc0 mm/mempolicy.c:2520
>   filemap_alloc_folio_noprof+0xdf/0x510 mm/filemap.c:1007
>   do_read_cache_folio+0x1c0/0x560 mm/filemap.c:3885
>   do_read_cache_page mm/filemap.c:3989 [inline]
>   read_cache_page+0x5d/0x170 mm/filemap.c:3998
>   read_mapping_page include/linux/pagemap.h:993 [inline]
>   inode_read_data+0xa7/0x480 fs/ntfs3/inode.c:1054
>   ntfs_fill_super+0x39c8/0x40b0 fs/ntfs3/super.c:1533
>   get_tree_bdev_flags+0x40e/0x4d0 fs/super.c:1692
>   vfs_get_tree+0x8f/0x2b0 fs/super.c:1815
>   do_new_mount+0x2a2/0x9e0 fs/namespace.c:3805
>   do_mount fs/namespace.c:4133 [inline]
>   __do_sys_mount fs/namespace.c:4344 [inline]
>   __se_sys_mount+0x317/0x410 fs/namespace.c:4321
>   do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>   do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
>   entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f4369ac030a
> Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb a6 e8 de 1a 00 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f4368d25e68 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
> RAX: ffffffffffffffda RBX: 00007f4368d25ef0 RCX: 00007f4369ac030a
> RDX: 0000200000000080 RSI: 000020000001f740 RDI: 00007f4368d25eb0
> RBP: 0000200000000080 R08: 00007f4368d25ef0 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 000020000001f740
> R13: 00007f4368d25eb0 R14: 000000000001f771 R15: 0000200000000100
>   </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:set_page_refcounted+0x142/0x1e0 mm/internal.h:491
> Code: 48 89 d8 48 25 ff 0f 00 00 74 21 e8 18 4e a4 ff e9 2c ff ff ff e8 0e 4e a4 ff 48 89 df 48 c7 c6 a0 47 17 8b e8 4f 05 e9 ff 90 <0f> 0b 48 89 df be 08 00 00 00 e8 3f 27 03 00 48 89 d8 48 c1 e8 03
> RSP: 0018:ffffc900065f7670 EFLAGS: 00010246
> RAX: 0ebb44fe4874cf00 RBX: ffffea00011839ff RCX: 0ebb44fe4874cf00
> RDX: 0000000000000001 RSI: ffffffff8d1dbecc RDI: ffff88802f581dc0
> RBP: 00000000000000ff R08: 0000000000000000 R09: 0000000000000000
> R10: dffffc0000000000 R11: ffffed1017124863 R12: 1ffffd4000230746
> R13: 0000000000000000 R14: ffffea0001183a33 R15: dffffc0000000000
> FS:  00007f4368d266c0(0000) GS:ffff888126c1e000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007feecfc73000 CR3: 0000000034c06000 CR4: 00000000003526f0
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> 
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
> 
> If you want syzbot to run the reproducer, reply with:
> #syz test: git://repo/address.git branch-or-commit-hash
> If you attach or paste a git patch, syzbot will apply it before testing.
> 
> If you want to overwrite report's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
> 
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report
> 
> If you want to undo deduplication, reply with:
> #syz undup
> 


-- 
Cheers,

David / dhildenb

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