[syzbot] [netfs?] kernel BUG in netfs_perform_write

[syzbot <syzbot+b73c7d94a151e2ee1e9b@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    b9a10f876409 Merge tag 'soc-fixes-6.17-2' of git://git.ker..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=148b6312580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d4703ac89d9e185a
dashboard link: https://syzkaller.appspot.com/bug?extid=b73c7d94a151e2ee1e9b
compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14dd1a42580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12eb0134580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f78fc7403c46/disk-b9a10f87.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a6cdb7126dd0/vmlinux-b9a10f87.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3e315b6f116e/bzImage-b9a10f87.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b73c7d94a151e2ee1e9b@syzkaller.appspotmail.com

 kill_anon_super+0x3a/0x60 fs/super.c:1282
 v9fs_kill_super+0x3d/0xa0 fs/9p/vfs_super.c:195
 deactivate_locked_super+0xc1/0x1a0 fs/super.c:474
 deactivate_super fs/super.c:507 [inline]
 deactivate_super+0xde/0x100 fs/super.c:503
 cleanup_mnt+0x225/0x450 fs/namespace.c:1375
------------[ cut here ]------------
kernel BUG at mm/filemap.c:1498!
Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 6039 Comm: syz.0.22 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
RIP: 0010:folio_unlock mm/filemap.c:1498 [inline]
RIP: 0010:folio_unlock+0xb3/0xd0 mm/filemap.c:1493
Code: b3 5c c9 ff 48 89 ef 31 f6 e8 f9 ed ff ff 5b 5d e9 a2 5c c9 ff e8 9d 5c c9 ff 48 c7 c6 60 19 b9 8b 48 89 ef e8 0e 0d 12 00 90 <0f> 0b 48 89 df e8 d3 bb 2f 00 e9 7b ff ff ff 66 66 2e 0f 1f 84 00
RSP: 0018:ffffc90002e97980 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: ffff88802f3cc880 RSI: ffffffff81f231a2 RDI: ffff88802f3cccc4
RBP: ffffea0001850e80 R08: 0000000000000001 R09: 0000000000000001
R10: ffffffff90ab5c97 R11: 0000000000000000 R12: ffff88805caf0f00
R13: ffffc90002e97de8 R14: ffffea0001850e80 R15: dffffc0000000000
FS:  000055555d2d5500(0000) GS:ffff8881246b8000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000c0071b4000 CR3: 000000007d73b000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 netfs_perform_write+0xacd/0x1e60 fs/netfs/buffered_write.c:407
 netfs_buffered_write_iter_locked fs/netfs/buffered_write.c:452 [inline]
 netfs_file_write_iter+0x495/0x570 fs/netfs/buffered_write.c:491
 v9fs_file_write_iter+0x9b/0x100 fs/9p/vfs_file.c:407
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x7d3/0x11d0 fs/read_write.c:686
 ksys_write+0x12a/0x250 fs/read_write.c:738
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f1f5f98ebe9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 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:00007ffd97e08798 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f1f5fbc5fa0 RCX: 00007f1f5f98ebe9
RDX: 0000000000000018 RSI: 0000200000000380 RDI: 0000000000000007
RBP: 00007f1f5fa11e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f1f5fbc5fa0 R14: 00007f1f5fbc5fa0 R15: 0000000000000003
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:folio_unlock mm/filemap.c:1498 [inline]
RIP: 0010:folio_unlock+0xb3/0xd0 mm/filemap.c:1493
Code: b3 5c c9 ff 48 89 ef 31 f6 e8 f9 ed ff ff 5b 5d e9 a2 5c c9 ff e8 9d 5c c9 ff 48 c7 c6 60 19 b9 8b 48 89 ef e8 0e 0d 12 00 90 <0f> 0b 48 89 df e8 d3 bb 2f 00 e9 7b ff ff ff 66 66 2e 0f 1f 84 00
RSP: 0018:ffffc90002e97980 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: ffff88802f3cc880 RSI: ffffffff81f231a2 RDI: ffff88802f3cccc4
RBP: ffffea0001850e80 R08: 0000000000000001 R09: 0000000000000001
R10: ffffffff90ab5c97 R11: 0000000000000000 R12: ffff88805caf0f00
R13: ffffc90002e97de8 R14: ffffea0001850e80 R15: dffffc0000000000
FS:  000055555d2d5500(0000) GS:ffff8881246b8000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000c0071b4000 CR3: 000000007d73b000 CR4: 00000000003526f0


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