syzbot


BUG: soft lockup in cpu_stopper_thread (2)

Status: moderation: reported on 2025/12/14 05:22
Subsystems: kernel
[Documentation on labels]
Reported-by: syzbot+8a24c20967f51cda0a1e@syzkaller.appspotmail.com
First crash: 87d, last: 24d
Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream BUG: soft lockup in cpu_stopper_thread kernel 1 1 2754d 2754d 0/29 closed as invalid on 2018/09/05 12:51
upstream INFO: rcu detected stall in cpu_stopper_thread (2) kernel 1 7 576d 626d 0/29 auto-obsoleted due to no activity on 2024/11/05 09:18

Sample crash report:
watchdog: BUG: soft lockup - CPU#1 stuck for 430s! [migration/1:21]
Modules linked in:
CPU: 1 UID: 0 PID: 21 Comm: migration/1 Tainted: G             L      syzkaller #0 PREEMPT 
Tainted: [L]=SOFTLOCKUP
Hardware name: ARM-Versatile Express
Stopper: multi_cpu_stop+0x0/0x170 kernel/stop_machine.c:198 <- __stop_cpus.constprop.0+0x68/0xa8
PC is at stop_machine_yield+0x0/0x10 kernel/stop_machine.c:196
LR is at multi_cpu_stop+0xd8/0x170 kernel/stop_machine.c:227
pc : [<80372078>]    lr : [<80372160>]    psr: 60000013
sp : df871ef0  ip : df871ef0  fp : df871f24
r10: 00000001  r9 : 00000000  r8 : 00000000
r7 : 8280c550  r6 : dfb21d8c  r5 : 00000001  r4 : dfb21da0
r3 : 00000001  r2 : 00000000  r1 : 00000008  r0 : 8280c550
Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
Control: 30c5387d  Table: 938efdc0  DAC: 00000000
Call trace: 
[<80372088>] (multi_cpu_stop) from [<80371e14>] (cpu_stopper_thread+0x94/0x130 kernel/stop_machine.c:512)
 r10:83218c00 r9:ddddb5f4 r8:dfb21d8c r7:ddddb5ec r6:80372088 r5:ddddb5e8
 r4:dfb21d54
[<80371d80>] (cpu_stopper_thread) from [<802887e8>] (smpboot_thread_fn+0x108/0x2f0 kernel/smpboot.c:160)
 r10:00000000 r9:00000001 r8:00000000 r7:00000001 r6:828fdb90 r5:830ccbc0
 r4:83218c00
[<802886e0>] (smpboot_thread_fn) from [<8027fd90>] (kthread+0x118/0x138 kernel/kthread.c:467)
 r9:830ccbc0 r8:802886e0 r7:df819d38 r6:83218c00 r5:830bf980 r4:830cccc0
[<8027fc78>] (kthread) from [<80200114>] (ret_from_fork+0x14/0x20 arch/arm/kernel/entry-common.S:137)
Exception stack(0xdf871fb0 to 0xdf871ff8)
1fa0:                                     00000000 00000000 00000000 00000000
1fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
1fe0: 00000000 00000000 00000000 00000000 00000013 00000000
 r9:00000000 r8:00000000 r7:00000000 r6:00000000 r5:8027fc78 r4:830cccc0
Sending NMI from CPU 1 to CPUs 0:

Crashes (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/02/10 21:19 upstream 72c395024dac a076df6f .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu2-arm32 BUG: soft lockup in cpu_stopper_thread
2025/12/12 02:46 upstream d358e5254674 a066d2bc .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu2-arm32 BUG: soft lockup in cpu_stopper_thread
2025/12/10 12:24 upstream c9b47175e913 48b27acc .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu2-arm32 BUG: soft lockup in cpu_stopper_thread
2025/12/10 05:20 upstream cb015814f8b6 fc20f974 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu2-arm32 BUG: soft lockup in cpu_stopper_thread
* Struck through repros no longer work on HEAD.