INFO: rcu detected stall in kthread (3)

Status: upstream: reported syz repro on 2026/03/22 04:20
Bug presence: origin:upstream
[Documentation on labels]
Reported-by: syzbot+613be74beec5938635ef@syzkaller.appspotmail.com
First crash: 140d, last: 40d
Fix bisection: failed (error log, bisect log)
  
▶ ▼ Bug presence (1)
Date Name Commit Repro Result
2026/03/22 upstream (ToT) 113ae7b4decc syz [report] INFO: rcu detected stall in schedule_timeout
▶ ▼ Similar bugs (10)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: rcu detected stall in kthread mm 1 1 2890d 2890d 0/29 closed as invalid on 2018/09/10 16:00
upstream INFO: rcu detected stall in kthread (3) kernel 1 12 520d 830d 0/29 auto-obsoleted due to no activity on 2025/06/05 06:00
linux-5.15 INFO: rcu detected stall in kthread (2) 1 1 242d 242d 0/3 auto-obsoleted due to no activity on 2026/03/20 03:20
linux-5.15 INFO: rcu detected stall in kthread 1 1 514d 514d 0/3 auto-obsoleted due to no activity on 2025/06/21 04:55
upstream INFO: rcu detected stall in kthread (6) prio:normal kernel 1 syz error 2 22d 18d 0/29 upstream: reported syz repro on 2026/07/22 10:23
upstream INFO: rcu detected stall in kthread (4) kernel 1 1 362d 362d 0/29 auto-obsoleted due to no activity on 2025/11/10 02:23
upstream INFO: rcu detected stall in kthread (5) kernel 1 2 180d 244d 0/29 auto-obsoleted due to no activity on 2026/05/11 18:17
upstream INFO: rcu detected stall in kthread (2) kernel 1 11 2796d 2885d 0/29 closed as dup on 2019/01/02 16:35
linux-6.6 INFO: rcu detected stall in kthread origin:lts-only 1 syz 1 20d 56d 0/2 upstream: reported syz repro on 2026/06/14 13:42
linux-4.19 INFO: rcu detected stall in kthread 1 2 1772d 1804d 0/1 auto-closed as invalid on 2022/01/30 14:43
▶ ▼ Last patch testing requests (3)
Created Duration User Patch Repo Result
2026/07/22 09:19 20m retest repro linux-5.15.y report log
2026/07/22 09:19 18m retest repro linux-5.15.y report log
2026/04/05 09:16 13m retest repro linux-5.15.y report log

Sample crash report:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P4287/1:b..l
	(detected by 0, t=10503 jiffies, g=8637, q=278)
task:kworker/1:10    state:R  running task     stack:25296 pid: 4287 ppid:     2 flags:0x00004000
Workqueue: events_power_efficient gc_worker
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5049 [inline]
 __schedule+0x11c3/0x4350 kernel/sched/core.c:6395
 preempt_schedule_irq+0xbb/0x160 kernel/sched/core.c:6799
 irqentry_exit+0x63/0x70 kernel/entry/common.c:432
 asm_sysvec_reschedule_ipi+0x16/0x20 arch/x86/include/asm/idtentry.h:681
RIP: 0010:check_kcov_mode kernel/kcov.c:183 [inline]
RIP: 0010:write_comp_data kernel/kcov.c:227 [inline]
RIP: 0010:__sanitizer_cov_trace_const_cmp4+0x32/0x80 kernel/kcov.c:293
Code: b4 79 89 7e 65 8b 15 b5 79 89 7e 81 e2 00 01 ff 00 74 11 81 fa 00 01 00 00 75 5b 83 b9 34 16 00 00 00 74 52 8b 91 10 16 00 00 <83> fa 03 75 47 48 8b 91 18 16 00 00 44 8b 89 14 16 00 00 49 c1 e1
RSP: 0018:ffffc9000305fad8 EFLAGS: 00000246
RAX: ffffffff88229730 RBX: 0000000000000001 RCX: ffff888029255940
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: ffffc9000305fc30 R08: ffffffff901cb15f R09: 1ffffffff203962b
R10: dffffc0000000000 R11: fffffbfff203962c R12: 0000000000063a17
R13: ffff8880769cbe00 R14: ffff88802b600000 R15: dffffc0000000000
 rcu_read_unlock include/linux/rcupdate.h:769 [inline]
 gc_worker+0xbe0/0x13d0 net/netfilter/nf_conntrack_core.c:1543
 process_one_work+0x867/0xff0 kernel/workqueue.c:2310
 worker_thread+0xad7/0x12a0 kernel/workqueue.c:2457
 kthread+0x42e/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>
rcu: rcu_preempt kthread starved for 10502 jiffies! g8637 f0x0 RCU_GP_DOING_FQS(6) ->state=0x0 ->cpu=0
rcu: 	Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
rcu: RCU grace-period kthread stack dump:
task:rcu_preempt     state:R  running task     stack:28176 pid:   15 ppid:     2 flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5049 [inline]
 __schedule+0x11c3/0x4350 kernel/sched/core.c:6395
 preempt_schedule_irq+0xbb/0x160 kernel/sched/core.c:6799
 irqentry_exit+0x63/0x70 kernel/entry/common.c:432
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:force_qs_rnp kernel/rcu/tree.c:2643 [inline]
RIP: 0010:rcu_gp_fqs kernel/rcu/tree.c:-1 [inline]
RIP: 0010:rcu_gp_fqs_loop+0x6f9/0x11f0 kernel/rcu/tree.c:1986
Code: e8 3c 64 58 00 4c 8b 23 eb 0f 4c 89 e7 e8 bf 94 5d 08 49 81 c4 00 04 00 00 48 63 1d d1 32 24 0c 48 83 fb 02 0f 83 27 06 00 00 <48> c1 e3 0a 48 8d 83 80 33 32 8c 49 39 c4 0f 83 98 07 00 00 65 48
RSP: 0018:ffffc90000d47cc0 EFLAGS: 00000297
RAX: af085b40e9241700 RBX: 0000000000000001 RCX: 0000000000000000
RDX: dffffc0000000000 RSI: ffffffff8a2b2be0 RDI: 00000000ffffffff
RBP: ffffc90000d47e10 R08: ffffffff8c323383 R09: 1ffffffff1864670
R10: dffffc0000000000 R11: fffffbfff1864671 R12: ffffffff8c323780
R13: 1ffffffff1801e30 R14: 0000000000000a06 R15: ffffffff8c3233d8
 rcu_gp_kthread+0x9a/0x370 kernel/rcu/tree.c:2145
 kthread+0x42e/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
NMI backtrace for cpu 0
CPU: 0 PID: 5194 Comm: syz.2.423 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Call Trace:
 <IRQ>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 nmi_cpu_backtrace+0x3a2/0x3d0 lib/nmi_backtrace.c:111
 nmi_trigger_cpumask_backtrace+0x163/0x280 lib/nmi_backtrace.c:62
 trigger_single_cpu_backtrace include/linux/nmi.h:166 [inline]
 rcu_check_gp_kthread_starvation+0x1cd/0x250 kernel/rcu/tree_stall.h:487
 print_other_cpu_stall+0x1110/0x1270 kernel/rcu/tree_stall.h:592
 check_cpu_stall kernel/rcu/tree_stall.h:745 [inline]
 rcu_pending kernel/rcu/tree.c:3936 [inline]
 rcu_sched_clock_irq+0x845/0x1120 kernel/rcu/tree.c:2619
 update_process_times+0x193/0x200 kernel/time/timer.c:2021
 tick_sched_handle kernel/time/tick-sched.c:254 [inline]
 tick_sched_timer+0x37d/0x560 kernel/time/tick-sched.c:1473
 __run_hrtimer kernel/time/hrtimer.c:1685 [inline]
 __hrtimer_run_queues+0x4b0/0xb60 kernel/time/hrtimer.c:1749
 hrtimer_interrupt+0x397/0x8b0 kernel/time/hrtimer.c:1811
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1097 [inline]
 __sysvec_apic_timer_interrupt+0x137/0x4a0 arch/x86/kernel/apic/apic.c:1114
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
 sysvec_apic_timer_interrupt+0x9b/0xc0 arch/x86/kernel/apic/apic.c:1108
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:__raw_spin_unlock_irq include/linux/spinlock_api_smp.h:169 [inline]
RIP: 0010:_raw_spin_unlock_irq+0x25/0x40 kernel/locking/spinlock.c:202
Code: 00 00 00 66 90 53 48 89 fb 48 83 c7 18 48 8b 74 24 08 e8 0e 14 9a f7 48 89 df e8 46 eb 9a f7 e8 e1 d5 bb f7 fb bf 01 00 00 00 <e8> 06 04 8f f7 65 8b 05 17 2b 3f 76 85 c0 74 02 5b c3 e8 54 38 3d
RSP: 0018:ffffc90005807bc0 EFLAGS: 00000282
RAX: fd34535d8fa5f700 RBX: ffff88805d41c0c0 RCX: fd34535d8fa5f700
RDX: dffffc0000000000 RSI: ffffffff8a2b2be0 RDI: 0000000000000001
RBP: 0000000000000000 R08: ffff88805d41c0c3 R09: 1ffff1100ba83818
R10: dffffc0000000000 R11: ffffed100ba83819 R12: dffffc0000000000
R13: ffff88805d41c0c0 R14: 0000000000000021 R15: 000000001c000004
 spin_unlock_irq include/linux/spinlock.h:414 [inline]
 get_signal+0x11f2/0x12e0 kernel/signal.c:2904
 arch_do_signal_or_restart+0xe6/0x12a0 arch/x86/kernel/signal.c:867
 handle_signal_work kernel/entry/common.c:154 [inline]
 exit_to_user_mode_loop+0x9e/0x130 kernel/entry/common.c:178
 exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:214
 __syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
 syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:307
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f13f43a1e59
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:00007f13f3a030e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 00007f13f461afa8 RCX: 00007f13f43a1e59
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007f13f461afa8
RBP: 00007f13f461afa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f13f461b038 R14: 00007ffc07bd1100 R15: 00007ffc07bd11e8
 </TASK>

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/06/30 00:24 linux-5.15.y eceeec79dbc6 6a0c72dc .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in kthread
2026/03/22 04:19 linux-5.15.y 91d48252ad4b 5b92003d .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in kthread
* Struck through repros no longer work on HEAD.