[Android 5.15] BUG: soft lockup in tc_modify_qdisc (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 13d6d33696ef Merge 5.15.200 into android13-5.15-lts
git tree: android13-5.15-lts
console output: https://syzkaller.appspot.com/x/log.txt?x=174afc02580000
kernel config: https://syzkaller.appspot.com/x/.config?x=deffac0a782f1cb0
dashboard link: https://syzkaller.appspot.com/bug?extid=b894e067a04eb2a0b2ce
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17e11fb2580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11d8a55a580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/49c205e65f10/disk-13d6d336.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e3df4a3942b9/vmlinux-13d6d336.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ac1426590472/bzImage-13d6d336.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b894e0...@syzkaller.appspotmail.com

RBP: 00007f6cbdecbb39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f6cbe0aefac R14: 00007f6cbe0aefa0 R15: 00007f6cbe0aefa0
</TASK>
watchdog: BUG: soft lockup - CPU#0 stuck for 225s! [syz.2.17:373]
Modules linked in:
CPU: 0 PID: 373 Comm: syz.2.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
RIP: 0010:qdisc_lookup+0x22d/0x4e0 net/sched/sch_api.c:-1
Code: 80 e1 07 80 c1 03 38 c1 7c b1 4c 89 e7 e8 bb 71 ce fd eb a7 e8 64 43 8f fd e9 ff 01 00 00 e8 5a 43 8f fd eb 05 e8 53 43 8f fd <4c> 8b 75 d0 49 81 c6 50 03 00 00 4c 89 f0 48 c1 e8 03 42 80 3c 28
RSP: 0018:ffffc90002096ec8 EFLAGS: 00000293
RAX: ffffffff83da8925 RBX: 00000000ffff0000 RCX: ffff88810e060000
RDX: 0000000000000000 RSI: 00000000ffff0000 RDI: 0000000000000000
RBP: ffffc90002096ef8 R08: ffff88810e060000 R09: 0000000000000002
R10: 00000000ffffffff R11: 0000000000000000 R12: 0000000000000000
R13: dffffc0000000000 R14: ffffffffffffffd8 R15: ffff88810f964000
FS: 000055556145a500(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000c006d86000 CR3: 000000011fd6f000 CR4: 00000000003506b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
qdisc_tree_reduce_backlog+0x111/0x340 net/sched/sch_api.c:784
fq_change+0xc5d/0x1250 net/sched/sch_fq.c:915
fq_init+0x3e3/0x5d0 net/sched/sch_fq.c:963
qdisc_create+0x803/0x11b0 net/sched/sch_api.c:1256
tc_modify_qdisc+0x8ad/0x1570 net/sched/sch_api.c:-1
rtnetlink_rcv_msg+0xa4b/0xce0 net/core/rtnetlink.c:5650
netlink_rcv_skb+0x1f5/0x440 net/netlink/af_netlink.c:2511
rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:5668
netlink_unicast_kernel net/netlink/af_netlink.c:1322 [inline]
netlink_unicast+0x876/0xa40 net/netlink/af_netlink.c:1348
netlink_sendmsg+0x879/0xb80 net/netlink/af_netlink.c:1922
sock_sendmsg_nosec net/socket.c:704 [inline]
__sock_sendmsg net/socket.c:716 [inline]
____sys_sendmsg+0x5b7/0x8f0 net/socket.c:2435
___sys_sendmsg+0x236/0x2e0 net/socket.c:2489
__sys_sendmsg net/socket.c:2518 [inline]
__do_sys_sendmsg net/socket.c:2527 [inline]
__se_sys_sendmsg net/socket.c:2525 [inline]
__x64_sys_sendmsg+0x206/0x2f0 net/socket.c:2525
x64_sys_call+0x4b/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:47
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f6cbde35629
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffdfc2a9f68 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f6cbe0aefa0 RCX: 00007f6cbde35629
RDX: 0000000020040080 RSI: 0000200000001200 RDI: 0000000000000005
RBP: 00007f6cbdecbb39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f6cbe0aefac R14: 00007f6cbe0aefa0 R15: 00007f6cbe0aefa0
</TASK>
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at native_safe_halt arch/x86/include/asm/irqflags.h:51 [inline]
NMI backtrace for cpu 1 skipped: idling at arch_safe_halt arch/x86/include/asm/irqflags.h:89 [inline]
NMI backtrace for cpu 1 skipped: idling at default_idle+0xf/0x20 arch/x86/kernel/process.c:729


---
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