[Android 6.1] BUG: soft lockup in tc_modify_qdisc (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 6bfa51973214 ANDROID: serial: qcom-geni: Add support for S..
git tree: android14-6.1
console output: https://syzkaller.appspot.com/x/log.txt?x=146d7006580000
kernel config: https://syzkaller.appspot.com/x/.config?x=19de17fcb07fab22
dashboard link: https://syzkaller.appspot.com/bug?extid=52b0ee3e9925623eb458
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=1133be4a580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13959b5a580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f9b9d632f3cc/disk-6bfa5197.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a2d8f05ae155/vmlinux-6bfa5197.xz
kernel image: https://storage.googleapis.com/syzbot-assets/84d5444f7348/bzImage-6bfa5197.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+52b0ee...@syzkaller.appspotmail.com

RBP: 00007fc76c232bd9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc76c416128 R14: 00007fc76c416090 R15: 00007fffc6c8b3d8
</TASK>
watchdog: BUG: soft lockup - CPU#1 stuck for 287s! [syz.4.21:427]
Modules linked in:
CPU: 1 PID: 427 Comm: syz.4.21 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
RIP: 0010:preempt_count arch/x86/include/asm/preempt.h:27 [inline]
RIP: 0010:check_kcov_mode kernel/kcov.c:182 [inline]
RIP: 0010:write_comp_data kernel/kcov.c:245 [inline]
RIP: 0010:__sanitizer_cov_trace_cmp4+0x10/0x90 kernel/kcov.c:287
Code: 0f 1f 84 00 00 00 00 00 66 90 90 90 90 90 90 90 90 90 90 90 90 b8 7d 47 2f 67 55 48 89 e5 48 8b 45 08 65 48 8b 15 00 ff 90 7e <65> 8b 0d 01 ff 90 7e 81 e1 00 01 ff 00 74 11 81 f9 00 01 00 00 75
RSP: 0018:ffffc90000e76e38 EFLAGS: 00000246
RAX: ffffffff84091355 RBX: 00000000ffff0000 RCX: 0000000000000000
RDX: ffff888111a83cc0 RSI: 00000000ffff0000 RDI: 00000000ffff0000
RBP: ffffc90000e76e38 R08: ffff888111a83cc0 R09: 0000000000000002
R10: 00000000ffffffff R11: 0000000000000000 R12: ffff888113b9e000
R13: dffffc0000000000 R14: ffff88811845d000 R15: 00000000ffff0000
FS: 00007fc76d1286c0(0000) GS:ffff8881f6f00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fcb2748aff8 CR3: 000000010d798000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
qdisc_match_from_root net/sched/sch_api.c:268 [inline]
qdisc_lookup_rcu+0x305/0x4e0 net/sched/sch_api.c:330
qdisc_tree_reduce_backlog+0x111/0x360 net/sched/sch_api.c:792
fq_change+0xc4c/0x1240 net/sched/sch_fq.c:912
fq_init+0x3e3/0x5d0 net/sched/sch_fq.c:960
qdisc_create+0x895/0x1180 net/sched/sch_api.c:1306
tc_modify_qdisc+0x900/0x19d0 net/sched/sch_api.c:-1
rtnetlink_rcv_msg+0xb3b/0xe00 net/core/rtnetlink.c:6150
netlink_rcv_skb+0x20f/0x460 net/netlink/af_netlink.c:2521
rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:6168
netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
netlink_unicast+0x8ab/0xa30 net/netlink/af_netlink.c:1345
netlink_sendmsg+0x8b9/0xbd0 net/netlink/af_netlink.c:1873
sock_sendmsg_nosec net/socket.c:716 [inline]
__sock_sendmsg net/socket.c:728 [inline]
____sys_sendmsg+0x5cc/0x990 net/socket.c:2508
___sys_sendmsg+0x2a2/0x360 net/socket.c:2562
__sys_sendmsg net/socket.c:2591 [inline]
__do_sys_sendmsg net/socket.c:2600 [inline]
__se_sys_sendmsg net/socket.c:2598 [inline]
__x64_sys_sendmsg+0x205/0x2d0 net/socket.c:2598
x64_sys_call+0x171/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:47
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fc76c19c799
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:00007fc76d128028 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fc76c416090 RCX: 00007fc76c19c799
RDX: 0000000000000010 RSI: 0000200000001200 RDI: 0000000000000006
RBP: 00007fc76c232bd9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc76c416128 R14: 00007fc76c416090 R15: 00007fffc6c8b3d8
</TASK>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at native_safe_halt arch/x86/include/asm/irqflags.h:51 [inline]
NMI backtrace for cpu 0 skipped: idling at arch_safe_halt arch/x86/include/asm/irqflags.h:89 [inline]
NMI backtrace for cpu 0 skipped: idling at default_idle+0xf/0x20 arch/x86/kernel/process.c:741


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