syzbot


BUG: soft lockup in tc_modify_qdisc (2)

Status: upstream: reported C repro on 2026/03/05 09:26
Bug presence: origin:lts
[Documentation on labels]
Reported-by: syzbot+52b0ee3e9925623eb458@syzkaller.appspotmail.com
First crash: 143d, last: 10d
Bug presence (2)
Date Name Commit Repro Result
2026/03/05 lts (merge base) 0182cb5b74ee C [report] BUG: soft lockup in tc_modify_qdisc
2026/03/05 upstream (ToT) c107785c7e8d C Didn't crash
Similar bugs (13)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
android-6-1 BUG: soft lockup in tc_modify_qdisc 1 C done done 53 884d 916d 0/2 auto-obsoleted due to no activity on 2024/02/06 04:01
android-5-15 BUG: soft lockup in tc_modify_qdisc (2) origin:lts 1 C 21 1d09h 67d 0/2 upstream: reported C repro on 2026/02/22 06:27
android-5-15 BUG: soft lockup in tc_modify_qdisc origin:lts 1 C done done 254 973d 1029d 0/2 auto-obsoleted due to no activity on 2023/11/09 01:01
linux-5.15 BUG: soft lockup in tc_modify_qdisc origin:upstream 1 C error 1 1062d 1062d 0/3 auto-obsoleted due to no activity on 2023/09/11 01:53
linux-6.1 INFO: rcu detected stall in tc_modify_qdisc 1 3 654d 693d 0/3 auto-obsoleted due to no activity on 2024/10/23 00:42
linux-6.1 BUG: soft lockup in tc_modify_qdisc origin:upstream 1 C done 1 1061d 1061d 3/3 fixed on 2023/07/10 11:22
android-5-10 BUG: soft lockup in tc_modify_qdisc 1 C done done 314 975d 1029d 0/2 auto-obsoleted due to no activity on 2023/11/07 07:54
upstream INFO: rcu detected stall in tc_modify_qdisc net 1 C done 634 6d03h 2101d 0/29 upstream: reported C repro on 2020/07/29 05:53
linux-6.1 INFO: rcu detected stall in tc_modify_qdisc (2) origin:upstream 1 C error 20 111d 539d 0/3 upstream: reported C repro on 2024/11/08 00:04
linux-5.15 INFO: rcu detected stall in tc_modify_qdisc origin:lts-only 1 C error 23 61d 625d 0/3 upstream: reported C repro on 2024/08/13 15:46
android-5-10 BUG: soft lockup in tc_modify_qdisc (2) 1 C 82 9d19h 237d 0/2 upstream: reported C repro on 2025/09/05 07:56
linux-6.6 INFO: rcu detected stall in tc_modify_qdisc 1 1 315d 315d 0/2 auto-obsoleted due to no activity on 2025/09/27 23:42
linux-6.6 INFO: rcu detected stall in tc_modify_qdisc (2) 1 1 144d 144d 0/2 auto-obsoleted due to no activity on 2026/03/17 12:53
Last patch testing requests (2)
Created Duration User Patch Repo Result
2026/04/20 01:08 19m retest repro android14-6.1 report log
2026/03/20 09:41 11m retest repro android14-6.1 report log

Sample crash report:
RBP: 00007efd85a32c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007efd85c15fac R14: 00007efd85c15fa0 R15: 00007efd85c15fa0
 </TASK>
watchdog: BUG: soft lockup - CPU#1 stuck for 287s! [syz.2.17:363]
Modules linked in:
CPU: 1 PID: 363 Comm: syz.2.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
RIP: 0010:check_kcov_mode kernel/kcov.c:184 [inline]
RIP: 0010:write_comp_data kernel/kcov.c:245 [inline]
RIP: 0010:__sanitizer_cov_trace_const_cmp4+0x30/0x90 kernel/kcov.c:313
Code: 45 08 65 48 8b 15 90 fa 90 7e 65 8b 0d 91 fa 90 7e 81 e1 00 01 ff 00 74 11 81 f9 00 01 00 00 75 5b 83 ba 6c 0b 00 00 00 74 52 <8b> 8a 48 0b 00 00 83 f9 03 75 47 48 8b 8a 50 0b 00 00 44 8b 8a 4c
RSP: 0018:ffffc900009a6e38 EFLAGS: 00000246
RAX: ffffffff8409a297 RBX: dffffc0000000000 RCX: 0000000000000000
RDX: ffff888113d49440 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc900009a6e38 R08: ffff888113d49440 R09: 0000000000000002
R10: 00000000ffffffff R11: 0000000000000000 R12: 00000000fffffff1
R13: ffff88812056a000 R14: ffff888120568400 R15: ffff88812056a040
FS:  000055555bee7500(0000) GS:ffff8881f6f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007efd85872140 CR3: 0000000121960000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 qdisc_tree_reduce_backlog+0x127/0x360 net/sched/sch_api.c:790
 fq_codel_change+0xb3f/0x1090 net/sched/sch_fq_codel.c:440
 fq_codel_init+0x384/0xa90 net/sched/sch_fq_codel.c:477
 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: 0033:0x7efd8599c819
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:00007ffd71423928 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007efd85c15fa0 RCX: 00007efd8599c819
RDX: 0000000000008840 RSI: 0000200000000740 RDI: 0000000000000005
RBP: 00007efd85a32c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007efd85c15fac R14: 00007efd85c15fa0 R15: 00007efd85c15fa0
 </TASK>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 367 Comm: kworker/u4:5 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Workqueue: events_unbound toggle_allocation_gate
RIP: 0010:get_current arch/x86/include/asm/current.h:15 [inline]
RIP: 0010:__sanitizer_cov_trace_pc+0x8/0x60 kernel/kcov.c:215
Code: 8b 3d fc 4c 21 06 48 89 de e8 e4 9b 44 00 5b 5d c3 00 90 90 90 90 90 90 90 90 90 90 90 b8 0c 67 40 a5 55 48 89 e5 48 8b 45 08 <65> 48 8b 0d b0 fe 90 7e 65 8b 15 b1 fe 90 7e 81 e2 00 01 ff 00 74
RSP: 0018:ffffc900009e7830 EFLAGS: 00000202
RAX: ffffffff8167ff39 RBX: dffffc0000000000 RCX: ffff888114c9bcc0
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: ffffc900009e7830 R08: ffff8881f6e390d7 R09: 1ffff1103edc721a
R10: 0000000000000000 R11: ffffffff8134c6c0 R12: 1ffff1103edc7218
R13: 1ffff1103ede78a5 R14: 0000000000000001 R15: ffff8881f6f3c528
FS:  0000000000000000(0000) GS:ffff8881f6e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00001357f4fe9010 CR3: 000000000700f000 CR4: 00000000003506b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 csd_lock_wait kernel/smp.c:453 [inline]
 smp_call_function_many_cond+0x8a9/0x980 kernel/smp.c:998
 on_each_cpu_cond_mask+0x43/0x80 kernel/smp.c:1165
 on_each_cpu include/linux/smp.h:71 [inline]
 text_poke_sync arch/x86/kernel/alternative.c:1574 [inline]
 text_poke_bp_batch+0x1cf/0x600 arch/x86/kernel/alternative.c:1774
 text_poke_flush arch/x86/kernel/alternative.c:1965 [inline]
 text_poke_finish+0x1a/0x30 arch/x86/kernel/alternative.c:1972
 arch_jump_label_transform_apply+0x15/0x30 arch/x86/kernel/jump_label.c:146
 __jump_label_update+0x37c/0x3a0 kernel/jump_label.c:451
 jump_label_update+0x39b/0x450 kernel/jump_label.c:797
 static_key_disable_cpuslocked+0xc9/0x1a0 kernel/jump_label.c:203
 static_key_disable+0x1a/0x30 kernel/jump_label.c:211
 toggle_allocation_gate+0x3a5/0x440 mm/kfence/core.c:834
 process_one_work+0x71f/0xc40 kernel/workqueue.c:2302
 worker_thread+0xa29/0x11e0 kernel/workqueue.c:2449
 kthread+0x281/0x320 kernel/kthread.c:386
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
 </TASK>

Crashes (5):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/04/05 19:49 android14-6.1 9ab204675a62 4440e7c2 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-6-1 BUG: soft lockup in tc_modify_qdisc
2026/03/05 09:22 android14-6.1 6bfa51973214 a9fe5c9e .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-6-1 BUG: soft lockup in tc_modify_qdisc
2026/03/22 17:04 android14-6.1 ddd5813c91fc 5b92003d .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 BUG: soft lockup in tc_modify_qdisc
2025/12/17 04:01 android14-6.1 66807f9400bc d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 BUG: soft lockup in tc_modify_qdisc
2025/12/08 21:50 android14-6.1 5ddae867b428 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 BUG: soft lockup in tc_modify_qdisc
* Struck through repros no longer work on HEAD.