[v6.6] general protection fault in qfq_qlen_notify

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 9247f4e6573a Linux 6.6.98
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=11b16382580000
kernel config: https://syzkaller.appspot.com/x/.config?x=cfe840f14e117c98
dashboard link: https://syzkaller.appspot.com/bug?extid=441df78958d6539a0e50
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/3855f6db0ca8/disk-9247f4e6.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/fe3d6afeb3a6/vmlinux-9247f4e6.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7d8784621ac6/bzImage-9247f4e6.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+441df7...@syzkaller.appspotmail.com

general protection fault, probably for non-canonical address 0xdffffc000000000b: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000058-0x000000000000005f]
CPU: 1 PID: 10109 Comm: syz.7.1176 Not tainted 6.6.98-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
RIP: 0010:list_empty include/linux/list.h:373 [inline]
RIP: 0010:qfq_qlen_notify+0x29/0x70 net/sched/sch_qfq.c:1425
Code: 90 f3 0f 1e fa 41 57 41 56 53 48 89 f3 49 89 fe e8 9c a4 ed f8 4c 8d 7b 58 4c 89 f8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df <80> 3c 08 00 74 08 4c 89 ff e8 59 53 46 f9 49 8b 07 4c 39 f8 74 1c
RSP: 0018:ffffc90003326de8 EFLAGS: 00010202
RAX: 000000000000000b RBX: 0000000000000000 RCX: dffffc0000000000
RDX: ffffc90017167000 RSI: 00000000000017e9 RDI: 00000000000017ea
RBP: dffffc0000000000 R08: ffff888021175a00 R09: 0000000000000002
R10: 00000000ffffffff R11: 0000000000000002 R12: 0000000000000000
R13: ffff888069db4000 R14: ffff888069db4000 R15: 0000000000000058
FS: 00007eff5242a6c0(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f12e9ae5000 CR3: 000000001d7df000 CR4: 00000000003506e0
Call Trace:
<TASK>
qdisc_tree_reduce_backlog+0x28b/0x470 net/sched/sch_api.c:810
hhf_change+0x817/0xd30 net/sched/sch_hhf.c:567
hhf_init+0x219/0x940 net/sched/sch_hhf.c:593
qdisc_create+0x8eb/0x1050 net/sched/sch_api.c:1322
tc_modify_qdisc+0xb13/0x1be0 net/sched/sch_api.c:-1
rtnetlink_rcv_msg+0x7c7/0xf10 net/core/rtnetlink.c:6475
netlink_rcv_skb+0x216/0x480 net/netlink/af_netlink.c:2537
netlink_unicast_kernel net/netlink/af_netlink.c:1323 [inline]
netlink_unicast+0x750/0x8c0 net/netlink/af_netlink.c:1349
netlink_sendmsg+0x8c1/0xbe0 net/netlink/af_netlink.c:1891
sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg net/socket.c:745 [inline]
____sys_sendmsg+0x5bf/0x950 net/socket.c:2595
___sys_sendmsg+0x220/0x290 net/socket.c:2649
__sys_sendmsg net/socket.c:2678 [inline]
__do_sys_sendmsg net/socket.c:2687 [inline]
__se_sys_sendmsg+0x1a5/0x270 net/socket.c:2685
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7eff5158e929
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:00007eff5242a038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007eff517b6080 RCX: 00007eff5158e929
RDX: 0000000000004000 RSI: 0000200000000280 RDI: 0000000000000003
RBP: 00007eff51610ca1 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000001 R14: 00007eff517b6080 R15: 00007ffd0d2e78d8
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:list_empty include/linux/list.h:373 [inline]
RIP: 0010:qfq_qlen_notify+0x29/0x70 net/sched/sch_qfq.c:1425
Code: 90 f3 0f 1e fa 41 57 41 56 53 48 89 f3 49 89 fe e8 9c a4 ed f8 4c 8d 7b 58 4c 89 f8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df <80> 3c 08 00 74 08 4c 89 ff e8 59 53 46 f9 49 8b 07 4c 39 f8 74 1c
RSP: 0018:ffffc90003326de8 EFLAGS: 00010202
RAX: 000000000000000b RBX: 0000000000000000 RCX: dffffc0000000000
RDX: ffffc90017167000 RSI: 00000000000017e9 RDI: 00000000000017ea
RBP: dffffc0000000000 R08: ffff888021175a00 R09: 0000000000000002
R10: 00000000ffffffff R11: 0000000000000002 R12: 0000000000000000
R13: ffff888069db4000 R14: ffff888069db4000 R15: 0000000000000058
FS: 00007eff5242a6c0(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f12e9ae5000 CR3: 000000001d7df000 CR4: 00000000003506e0
----------------
Code disassembly (best guess):
0: 90 nop
1: f3 0f 1e fa endbr64
5: 41 57 push %r15
7: 41 56 push %r14
9: 53 push %rbx
a: 48 89 f3 mov %rsi,%rbx
d: 49 89 fe mov %rdi,%r14
10: e8 9c a4 ed f8 call 0xf8eda4b1
15: 4c 8d 7b 58 lea 0x58(%rbx),%r15
19: 4c 89 f8 mov %r15,%rax
1c: 48 c1 e8 03 shr $0x3,%rax
20: 48 b9 00 00 00 00 00 movabs $0xdffffc0000000000,%rcx
27: fc ff df
* 2a: 80 3c 08 00 cmpb $0x0,(%rax,%rcx,1) <-- trapping instruction
2e: 74 08 je 0x38
30: 4c 89 ff mov %r15,%rdi
33: e8 59 53 46 f9 call 0xf9465391
38: 49 8b 07 mov (%r15),%rax
3b: 4c 39 f8 cmp %r15,%rax
3e: 74 1c je 0x5c


---
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 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

[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.