[Android 6.1] general protection fault in __is_local_mountpoint

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 92668decd5e0 UPSTREAM: locking/rtmutex: Skip remove_waiter..
git tree: android14-6.1
console+strace: https://syzkaller.appspot.com/x/log.txt?x=172f2679580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6af0777879025b2
dashboard link: https://syzkaller.appspot.com/bug?extid=a37efc966ac7bc8b00cf
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10af2679580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=144836c6580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d489fb35aec8/disk-92668dec.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/33e640edad62/vmlinux-92668dec.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e0bb511e52c2/bzImage-92668dec.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/91ceadcd49ff/mount_0.gz
fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=178836c6580000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a37efc...@syzkaller.appspotmail.com

general protection fault, probably for non-canonical address 0xdffffc0000000003: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000018-0x000000000000001f]
CPU: 0 PID: 320 Comm: syz-executor226 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:__is_local_mountpoint+0x56/0x1a0 fs/namespace.c:749
Code: 49 81 c6 48 08 00 00 4c 89 f0 48 c1 e8 03 80 3c 18 00 74 08 4c 89 f7 e8 98 3f ef ff 4d 8b 36 49 83 c6 18 4c 89 f0 48 c1 e8 03 <80> 3c 18 00 74 08 4c 89 f7 e8 7c 3f ef ff 4d 8b 3e 48 c7 c7 20 90
RSP: 0018:ffffc90000f47738 EFLAGS: 00010206
RAX: 0000000000000003 RBX: dffffc0000000000 RCX: ffff888110888000
RDX: 0000000000000000 RSI: 0000000000010000 RDI: ffff88810b7eb220
RBP: ffffc90000f47770 R08: ffff88810c05e34f R09: 1ffff1102180bc69
R10: dffffc0000000000 R11: ffffed102180bc6a R12: 1ffff1102180b0e8
R13: 0000000000010000 R14: 0000000000000018 R15: 1ffff110216fd644
FS: 0000000000000000(0000) GS:ffff8881f6e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000001000 CR3: 0000000123a26000 CR4: 00000000003506b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
is_local_mountpoint fs/mount.h:141 [inline]
vfs_rmdir+0x12d/0x4f0 fs/namei.c:4190
incfs_kill_sb+0xfe/0x210 fs/incfs/vfs.c:1995
deactivate_locked_super+0xb5/0x120 fs/super.c:336
deactivate_super+0xaf/0xe0 fs/super.c:367
cleanup_mnt+0x45e/0x4e0 fs/namespace.c:1192
__cleanup_mnt+0x19/0x20 fs/namespace.c:1199
task_work_run+0x1e1/0x250 kernel/task_work.c:203
exit_task_work include/linux/task_work.h:39 [inline]
do_exit+0xaf2/0x2850 kernel/exit.c:887
do_group_exit+0x21b/0x2e0 kernel/exit.c:1030
get_signal+0x167c/0x1700 kernel/signal.c:2895
arch_do_signal_or_restart+0xd1/0x11c0 arch/x86/kernel/signal.c:871
exit_to_user_mode_loop+0x7a/0xb0 kernel/entry/common.c:174
exit_to_user_mode_prepare+0x87/0xd0 kernel/entry/common.c:210
__syscall_exit_to_user_mode_work kernel/entry/common.c:292 [inline]
syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:303
do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:82
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f47bdee0c89
Code: Unable to access opcode bytes at 0x7f47bdee0c5f.
RSP: 002b:00007f47bdeb5218 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 00007f47bdf88e28 RCX: 00007f47bdee0c89
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007f47bdf88e28
RBP: 00007f47bdf88e20 R08: 33203a6b63617473 R09: 33203a6b63617473
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f47bdf5997c
R13: 0000200000000b80 R14: 0000200000000040 R15: 0030656c69662f2e
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:__is_local_mountpoint+0x56/0x1a0 fs/namespace.c:749
Code: 49 81 c6 48 08 00 00 4c 89 f0 48 c1 e8 03 80 3c 18 00 74 08 4c 89 f7 e8 98 3f ef ff 4d 8b 36 49 83 c6 18 4c 89 f0 48 c1 e8 03 <80> 3c 18 00 74 08 4c 89 f7 e8 7c 3f ef ff 4d 8b 3e 48 c7 c7 20 90
RSP: 0018:ffffc90000f47738 EFLAGS: 00010206
RAX: 0000000000000003 RBX: dffffc0000000000 RCX: ffff888110888000
RDX: 0000000000000000 RSI: 0000000000010000 RDI: ffff88810b7eb220
RBP: ffffc90000f47770 R08: ffff88810c05e34f R09: 1ffff1102180bc69
R10: dffffc0000000000 R11: ffffed102180bc6a R12: 1ffff1102180b0e8
R13: 0000000000010000 R14: 0000000000000018 R15: 1ffff110216fd644
FS: 0000000000000000(0000) GS:ffff8881f6f00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f47bdec0224 CR3: 0000000121215000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
0: 49 81 c6 48 08 00 00 add $0x848,%r14
7: 4c 89 f0 mov %r14,%rax
a: 48 c1 e8 03 shr $0x3,%rax
e: 80 3c 18 00 cmpb $0x0,(%rax,%rbx,1)
12: 74 08 je 0x1c
14: 4c 89 f7 mov %r14,%rdi
17: e8 98 3f ef ff call 0xffef3fb4
1c: 4d 8b 36 mov (%r14),%r14
1f: 49 83 c6 18 add $0x18,%r14
23: 4c 89 f0 mov %r14,%rax
26: 48 c1 e8 03 shr $0x3,%rax
* 2a: 80 3c 18 00 cmpb $0x0,(%rax,%rbx,1) <-- trapping instruction
2e: 74 08 je 0x38
30: 4c 89 f7 mov %r14,%rdi
33: e8 7c 3f ef ff call 0xffef3fb4
38: 4d 8b 3e mov (%r14),%r15
3b: 48 rex.W
3c: c7 .byte 0xc7
3d: c7 (bad)
3e: 20 .byte 0x20
3f: 90 nop


---
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 syzk...@googlegroups.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