BUG: soft lockup in dummy_timer (2)

Status: moderation: reported on 2026/09/13 06:30
Subsystems: usb
Labels: prio:normal
[Documentation on labels]
Reported-by: syzbot+34d5f2088713efc09d6b@syzkaller.appspotmail.com
First crash: 4d02h, last: 4d02h
✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision
aaa9472a assessment-security DenialOfService: ✅ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌ BUG: soft lockup in dummy_timer (2) 2026/09/13 00:00 2026/09/13 00:00 2026/09/13 00:54 70a60e12
efea32cc assessment-security 💥 BUG: soft lockup in dummy_timer (2) 2026/09/11 00:00 2026/09/11 00:00 2026/09/11 00:51 1fe56c0a
Similar bugs (4)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: rcu detected stall in dummy_timer (4) usb 1 syz, C inconclusive done 25 365d 1527d 29/29 fixed on 2025/11/14 12:00
upstream BUG: soft lockup in dummy_timer usb 1 344 207d 275d 0/29 auto-obsoleted due to no activity on 2026/04/29 01:58
linux-5.15 INFO: rcu detected stall in dummy_timer 1 syz, C error 6 331d 1238d 0/3 auto-obsoleted due to no activity on 2026/01/24 13:15
upstream INFO: rcu detected stall in dummy_timer (3) usb 1 syz, C error 132 1663d 2251d 20/29 fixed on 2022/03/08 16:11

Sample crash report:
RBP: 00007ffe3e8dc74c R08: 0000000000000000 R09: 0000000000000001
R10: 00005555665b47d0 R11: 0000000000000246 R12: 0000000000000001
R13: 00000000000927c0 R14: 0000000000055e5d R15: 00007ffe3e8dc7a0
 </TASK>
ip6_tunnel: ip6gre1 xmit: Local address not yet configured!
watchdog: BUG: soft lockup - CPU#1 stuck for 245s! [syz-executor:5614]
Modules linked in:
irq event stamp: 21938471
hardirqs last  enabled at (21938470): [<ffffffff8bd26bc2>] __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:210 [inline]
hardirqs last  enabled at (21938470): [<ffffffff8bd26bc2>] _raw_spin_unlock_irqrestore+0x52/0x80 kernel/locking/spinlock.c:221
hardirqs last disabled at (21938471): [<ffffffff8bcf613e>] sysvec_apic_timer_interrupt+0xe/0xc0 arch/x86/kernel/apic/apic.c:1062
softirqs last  enabled at (21938462): [<ffffffff81ca135a>] __do_softirq kernel/softirq.c:679 [inline]
softirqs last  enabled at (21938462): [<ffffffff81ca135a>] invoke_softirq kernel/softirq.c:519 [inline]
softirqs last  enabled at (21938462): [<ffffffff81ca135a>] __irq_exit_rcu+0x16a/0x210 kernel/softirq.c:758
softirqs last disabled at (21938465): [<ffffffff81ca135a>] __do_softirq kernel/softirq.c:679 [inline]
softirqs last disabled at (21938465): [<ffffffff81ca135a>] invoke_softirq kernel/softirq.c:519 [inline]
softirqs last disabled at (21938465): [<ffffffff81ca135a>] __irq_exit_rcu+0x16a/0x210 kernel/softirq.c:758
CPU: 1 UID: 0 PID: 5614 Comm: syz-executor Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/05/2026
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:211 [inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0x31/0x80 kernel/locking/spinlock.c:221
Code: f5 53 48 8b 74 24 10 48 89 fb 48 83 c7 18 e8 76 bd 14 f6 48 89 df e8 fe 13 15 f6 f7 c5 00 02 00 00 75 23 9c 58 f6 c4 02 75 37 <bf> 01 00 00 00 e8 75 09 04 f6 65 48 83 3d 74 f4 b9 08 00 74 16 5b
RSP: 0018:ffffc90000a18c40 EFLAGS: 00000246
RAX: 0000000000000002 RBX: ffff88802aee4000 RCX: 0000000000000004
RDX: 0000000000000102 RSI: ffffffff8e3f2a8e RDI: ffffffff8c622680
RBP: 0000000000000246 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000001 R12: 0000000000000000
R13: ffff88802aee4000 R14: ffff88802b3fc4a3 R15: ffff88802b3fc410
FS:  00005555665b4500(0000) GS:ffff888123c5a000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fb10f1556c8 CR3: 000000005a395000 CR4: 0000000000350ef0
Call Trace:
 <IRQ>
 spin_unlock_irqrestore include/linux/spinlock.h:425 [inline]
 dummy_timer+0x1d89/0x3700 drivers/usb/gadget/udc/dummy_hcd.c:2036
 __run_hrtimer kernel/time/hrtimer.c:2067 [inline]
 __hrtimer_run_queues+0x462/0x9c0 kernel/time/hrtimer.c:2124
 hrtimer_run_softirq+0x1ca/0x360 kernel/time/hrtimer.c:2141
 handle_softirqs+0x1e6/0x9d0 kernel/softirq.c:645
 __do_softirq kernel/softirq.c:679 [inline]
 invoke_softirq kernel/softirq.c:519 [inline]
 __irq_exit_rcu+0x16a/0x210 kernel/softirq.c:758
 irq_exit_rcu+0x9/0x30 kernel/softirq.c:775
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1062 [inline]
 sysvec_apic_timer_interrupt+0xa3/0xc0 arch/x86/kernel/apic/apic.c:1062
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674
RIP: 0010:csd_lock_wait kernel/smp.c:363 [inline]
RIP: 0010:csd_lock kernel/smp.c:396 [inline]
RIP: 0010:smp_call_function_many_cond+0x57c/0x18c0 kernel/smp.c:944
Code: 00 00 00 00 00 fc ff df 48 89 ea 49 89 ec 48 c1 ea 03 41 83 e4 07 4c 8d 2c 02 41 83 c4 03 e8 0b c3 0c 00 f3 90 41 0f b6 45 00 <41> 38 c4 7c 08 84 c0 0f 85 51 11 00 00 44 8b 73 08 31 ff 41 83 e6
RSP: 0018:ffffc9000410f578 EFLAGS: 00000293
RAX: 0000000000000000 RBX: ffff8880b8443c80 RCX: 0000000000000001
RDX: ffff8880772b8000 RSI: ffffffff81ff2ce5 RDI: ffff8880772b8000
RBP: ffff8880b8443c88 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000003
R13: ffffed1017088791 R14: 0000000000000001 R15: 0000000000000000
 __flush_tlb_multi arch/x86/include/asm/paravirt.h:46 [inline]
 flush_tlb_multi arch/x86/mm/tlb.c:1361 [inline]
 flush_tlb_mm_range+0x3c9/0x1360 arch/x86/mm/tlb.c:1435
 dup_mmap+0x157b/0x2370 mm/mmap.c:1884
 dup_mm kernel/fork.c:1543 [inline]
 copy_mm kernel/fork.c:1595 [inline]
 copy_process+0x4811/0x8370 kernel/fork.c:2307
 kernel_clone+0x176/0x9d0 kernel/fork.c:2766
 __do_sys_clone+0xd9/0x120 kernel/fork.c:2908
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb10e3c6bd2
Code: 89 e7 e8 71 8b f7 ff 45 31 c0 31 d2 31 f6 64 48 8b 04 25 10 00 00 00 bf 11 00 20 01 4c 8d 90 d0 02 00 00 b8 38 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 66 89 c5 85 c0 75 3b 64 48 8b 04 25 10 00 00
RSP: 002b:00007ffe3e8dc5c0 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 00007ffe3e8dc5c0 RCX: 00007fb10e3c6bd2
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000001200011
RBP: 00007ffe3e8dc74c R08: 0000000000000000 R09: 0000000000000001
R10: 00005555665b47d0 R11: 0000000000000246 R12: 0000000000000001
R13: 00000000000927c0 R14: 0000000000055e5d R15: 00007ffe3e8dc7a0
 </TASK>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 11927 Comm: syz.1.2316 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/05/2026
RIP: 0010:_raw_spin_lock_irqsave+0x43/0x60 kernel/locking/spinlock.c:182
Code: e8 b2 6d 04 f6 ff 74 24 10 48 8d 7b 18 45 31 c9 31 c9 41 b8 01 00 00 00 31 d2 31 f6 e8 f6 bb 14 f6 48 89 df e8 0e 14 15 f6 58 <48> 89 e8 5b 5d e9 7e d9 3d f5 e8 1e dd 41 f6 eb c0 66 66 2e 0f 1f
RSP: 0018:ffffc90000007d48 EFLAGS: 00000092
RAX: ffffffff85339084 RBX: ffffffff9bc31970 RCX: ffffffff81e77cb8
RDX: 1ffffffff3786330 RSI: 0000000000000004 RDI: ffffc90000007cd0
RBP: 0000000000000012 R08: 0000000000000001 R09: fffff52000000f9a
R10: 0000000000000003 R11: 0000000000000000 R12: dffffc0000000000
R13: ffff888034b95300 R14: 0000000000000001 R15: 1ffff92000000fb0
FS:  0000555565bcb500(0000) GS:ffff888123b5a000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000040 CR3: 0000000075c1d000 CR4: 0000000000350ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
 <IRQ>
 debug_object_activate+0x144/0x4b0 lib/debugobjects.c:873
 debug_hrtimer_activate kernel/time/hrtimer.c:486 [inline]
 debug_activate kernel/time/hrtimer.c:529 [inline]
 enqueue_hrtimer+0x75/0x2f0 kernel/time/hrtimer.c:1136
 __run_hrtimer kernel/time/hrtimer.c:2083 [inline]
 __hrtimer_run_queues+0x6ed/0x9c0 kernel/time/hrtimer.c:2124
 hrtimer_interrupt+0x441/0xaa0 kernel/time/hrtimer.c:2243
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1051 [inline]
 __sysvec_apic_timer_interrupt+0x109/0x470 arch/x86/kernel/apic/apic.c:1068
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1062 [inline]
 sysvec_apic_timer_interrupt+0x9e/0xc0 arch/x86/kernel/apic/apic.c:1062
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674
RIP: 0010:kasan_byte_accessible+0x18/0x30 mm/kasan/generic.c:212
Code: 1f 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 40 d6 48 b8 00 00 00 00 00 fc ff df 48 c1 ef 03 48 01 c7 0f b6 07 <3c> 07 0f 96 c0 e9 39 13 92 fe 66 66 2e 0f 1f 84 00 00 00 00 00 0f
RSP: 0018:ffffc9000494fa10 EFLAGS: 00000282
RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff8bd0b1da RDI: fffffbfff1d95864
RBP: ffffffff8ecac320 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffffffff8bd0b1da
R13: 0000000000000001 R14: 0000000000000000 R15: 0000000000000000
 __kasan_check_byte+0x13/0x50 mm/kasan/common.c:573
 kasan_check_byte include/linux/kasan.h:402 [inline]
 lock_acquire kernel/locking/lockdep.c:5916 [inline]
 lock_acquire+0x132/0x380 kernel/locking/lockdep.c:5899
 sched_submit_work kernel/sched/core.c:7311 [inline]
 schedule+0x17a/0x2c0 kernel/sched/core.c:7367
 futex_do_wait+0x88/0x180 kernel/futex/waitwake.c:387
 __futex_wait+0x1c4/0x300 kernel/futex/waitwake.c:722
 futex_wait+0xe6/0x370 kernel/futex/waitwake.c:750
 do_futex+0x265/0x440 kernel/futex/syscalls.c:133
 __do_sys_futex kernel/futex/syscalls.c:210 [inline]
 __se_sys_futex kernel/futex/syscalls.c:191 [inline]
 __x64_sys_futex+0x34f/0x4d0 kernel/futex/syscalls.c:191
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f6a0779e159
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:00007ffd3d3e5d78 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: ffffffffffffffda RBX: 0000000000055e84 RCX: 00007f6a0779e159
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007f6a07a25fac
RBP: 0000000000000032 R08: 0000000000000001 R09: 0000000000000000
R10: 00007ffd3d3e5e80 R11: 0000000000000246 R12: 00007ffd3d3e5ea0
R13: 00007f6a07a25fac R14: 0000000000055eb6 R15: 00007ffd3d3e5e80
 </TASK>

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/09 06:27 upstream 893e11787f78 8387c273 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-badwrites-root BUG: soft lockup in dummy_timer
* Struck through repros no longer work on HEAD.