INFO: rcu detected stall in kcompactd

Status: upstream: reported on 2026/08/29 05:06
Reported-by: syzbot+05405378ab79e6cc852f@syzkaller.appspotmail.com
First crash: 2d04h, last: 1d06h
▶ ▼ Similar bugs (5)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: rcu detected stall in kcompactd mm 1 1 1115d 1115d 0/29 auto-obsoleted due to no activity on 2023/11/10 08:17
linux-6.1 INFO: rcu detected stall in kcompactd 1 1 810d 810d 0/3 auto-obsoleted due to no activity on 2024/09/19 19:09
upstream INFO: rcu detected stall in kcompactd (2) mm 1 syz, C error unreliable 6 641d 821d 0/29 auto-obsoleted due to no activity on 2025/03/08 05:35
upstream INFO: rcu detected stall in kcompactd (3) mm 1 2 268d 301d 0/29 auto-obsoleted due to no activity on 2026/03/05 20:24
upstream BUG: soft lockup in kcompactd kvm 1 1 1762d 1758d 0/29 auto-closed as invalid on 2022/01/31 12:36

Sample crash report:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	0-...!: (1 GPs behind) idle=2dd/1/0x4000000000000002 softirq=18259/18260 fqs=506 
	(detected by 1, t=10505 jiffies, g=23505, q=1755)
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 7731 Comm: dhcpcd-run-hook Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:debug_smp_processor_id+0x0/0x10 lib/smp_processor_id.c:60
Code: 32 8a e8 43 01 00 00 65 c7 05 58 f0 42 76 00 00 00 00 48 c7 c7 00 ea 32 8a e8 2c 01 00 00 65 ff 0d 41 f0 42 76 5b c3 00 00 cc <48> c7 c7 60 43 7a 8a 48 c7 c6 a0 43 7a 8a eb 00 55 41 57 41 56 53
RSP: 0000:ffffc90003f7f200 EFLAGS: 00000002
RAX: 0000000000000003 RBX: ffff8880b903b1f0 RCX: ffffffff962f5f03
RDX: ffffea0000000000 RSI: 0000000000000000 RDI: 0000000000000001
RBP: 0000000000000000 R08: ffff8880b903b1fb R09: 1ffff1101720763f
R10: dffffc0000000000 R11: ffffed1017207640 R12: 0000000000000000
R13: dffffc0000000001 R14: 0000000000000000 R15: ffff8880b903b1f8
FS:  00007fd539fbec80(0000) GS:ffff8880b9000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fff149580a8 CR3: 0000000071c35000 CR4: 00000000003506f0
DR0: 0000200000000300 DR1: 0000200000000300 DR2: 0000200000000300
DR3: 0000200000000300 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
 <TASK>
 irq_work_queue_on+0x100/0x220 kernel/irq_work.c:104
 rcu_read_unlock_special+0x377/0x4a0 kernel/rcu/tree_plugin.h:667
 __rcu_read_unlock+0x78/0xd0 kernel/rcu/tree_plugin.h:422
 rcu_read_unlock include/linux/rcupdate.h:772 [inline]
 __perf_event_output kernel/events/core.c:7823 [inline]
 perf_event_output_forward+0x255/0x2e0 kernel/events/core.c:7832
 __perf_event_overflow+0x35f/0x550 kernel/events/core.c:9525
 perf_swevent_overflow kernel/events/core.c:9601 [inline]
 perf_swevent_event+0x4b8/0x540 kernel/events/core.c:9639
 perf_tp_event+0x324/0xbe0 kernel/events/core.c:10057
 perf_trace_run_bpf_submit+0xf3/0x1c0 kernel/events/core.c:10031
 perf_trace_preemptirq_template+0x2aa/0x360 include/trace/events/preemptirq.h:14
 trace_irq_enable_rcuidle+0x108/0x180 include/trace/events/preemptirq.h:40
 trace_hardirqs_on+0x57/0x80 kernel/trace/trace_preemptirq.c:44
 asm_sysvec_irq_work+0x16/0x20 arch/x86/include/asm/idtentry.h:713
RIP: 0010:rcu_read_unlock_special+0x7f/0x4a0 kernel/rcu/tree_plugin.h:674
Code: eb 03 48 b8 f1 f1 f1 f1 f8 f2 f2 f2 4a 89 04 2b 42 c7 44 2b 08 f8 f3 f3 f3 65 44 8b 35 f2 0f 9d 7e 41 f7 c6 00 00 f0 00 74 40 <48> c7 44 24 20 0e 36 e0 45 4a c7 04 2b 00 00 00 00 42 c7 44 2b 08
RSP: 0000:ffffc90003f7fa00 EFLAGS: 00000206
RAX: 6dc3fbf7fbeff400 RBX: 1ffff920007eff44 RCX: 6dc3fbf7fbeff400
RDX: dffffc0000000000 RSI: ffffffff8a2b2be0 RDI: ffffffff8a7a43c0
RBP: ffffc90003f7fad0 R08: ffffffff901ef0c7 R09: 1ffffffff203de18
R10: dffffc0000000000 R11: fffffbfff203de19 R12: ffffffff8c323400
R13: dffffc0000000000 R14: 0000000000000246 R15: 0000000000000001
 __rcu_read_unlock+0x78/0xd0 kernel/rcu/tree_plugin.h:422
 rcu_read_unlock include/linux/rcupdate.h:772 [inline]
 __unlock_page_memcg+0xea/0x100 mm/memcontrol.c:2093
 wp_page_copy+0xf34/0x2090 mm/memory.c:3148
 handle_pte_fault mm/memory.c:4668 [inline]
 __handle_mm_fault mm/memory.c:4785 [inline]
 handle_mm_fault+0x1fbd/0x4440 mm/memory.c:4883
 do_user_addr_fault+0x494/0xc90 arch/x86/mm/fault.c:1355
 handle_page_fault arch/x86/mm/fault.c:1443 [inline]
 exc_page_fault+0x60/0x100 arch/x86/mm/fault.c:1496
 asm_exc_page_fault+0x22/0x30 arch/x86/include/asm/idtentry.h:606
RIP: 0033:0x7fd53a2b5268
Code: 8b 54 24 20 8b 74 24 08 48 8b bc 24 90 00 00 00 e8 8f ed ff ff 85 c0 74 37 80 7b 47 01 75 07 83 7c 24 14 00 7e 2a 48 8b 7b 38 <6a> 01 5e e8 40 2f fc ff 8b 4c 24 34 48 8b 54 24 20 8b 74 24 08 48
RSP: 002b:00007fff149580b0 EFLAGS: 00010202
RAX: 0000000000000001 RBX: 00005586d8ff6910 RCX: 0000000000000000
RDX: 00005586d8ff6910 RSI: 0000000000000001 RDI: 00007fff14958900
RBP: 00005586d8ff6e60 R08: 00007fff14957f70 R09: 00005586d8ff6e60
R10: 0000000000000000 R11: 0000000000000202 R12: 00005586d9006e68
R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000000000
 </TASK>
rcu: rcu_preempt kthread starved for 7975 jiffies! g23505 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
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:27248 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
 schedule+0x11b/0x1e0 kernel/sched/core.c:6478
 schedule_timeout+0x184/0x2d0 kernel/time/timer.c:2117
 rcu_gp_fqs_loop+0x2be/0x11f0 kernel/rcu/tree.c:1972
 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 1
CPU: 1 PID: 30 Comm: kcompactd0 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
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:native_safe_halt arch/x86/include/asm/irqflags.h:51 [inline]
RIP: 0010:arch_safe_halt arch/x86/include/asm/irqflags.h:89 [inline]
RIP: 0010:kvm_wait+0x159/0x1b0 arch/x86/kernel/kvm.c:918
Code: 89 df 48 89 f8 48 c1 e8 03 42 0f b6 04 30 84 c0 75 4b 0f b6 1f e8 e7 8e 4a 00 44 38 e3 75 10 66 90 0f 00 2d c9 d9 f3 08 fb f4 <e9> 16 ff ff ff fb e9 10 ff ff ff e8 17 aa 8b 08 89 f9 80 e1 07 38
RSP: 0018:ffffc90000e5ee80 EFLAGS: 00000246
RAX: 2184eb7f63c8bf00 RBX: 0000000000000003 RCX: 2184eb7f63c8bf00
RDX: dffffc0000000000 RSI: ffffffff8a2b2be0 RDI: ffffffff8a7a43c0
RBP: ffffc90000e5ef30 R08: ffffffff901ef0c7 R09: 1ffffffff203de18
R10: dffffc0000000000 R11: fffffbfff203de19 R12: 0000000000000003
R13: dffffc0000000000 R14: dffffc0000000000 R15: 1ffff920001cbdd0
 pv_wait arch/x86/include/asm/paravirt.h:597 [inline]
 pv_wait_head_or_lock kernel/locking/qspinlock_paravirt.h:470 [inline]
 __pv_queued_spin_lock_slowpath+0x605/0x9b0 kernel/locking/qspinlock.c:508
 pv_queued_spin_lock_slowpath arch/x86/include/asm/paravirt.h:585 [inline]
 queued_spin_lock_slowpath+0x43/0x50 arch/x86/include/asm/qspinlock.h:51
 queued_spin_lock include/asm-generic/qspinlock.h:85 [inline]
 do_raw_spin_lock+0x265/0x2f0 kernel/locking/spinlock_debug.c:115
 page_vma_mapped_walk+0x13ee/0x16e0 mm/page_vma_mapped.c:-1
 try_to_migrate_one+0x34b/0xdc0 mm/rmap.c:1772
 rmap_walk_anon+0x38a/0x570 mm/rmap.c:2323
 try_to_migrate+0x4a0/0x5a0 mm/rmap.c:-1
 __unmap_and_move mm/migrate.c:1072 [inline]
 unmap_and_move mm/migrate.c:1218 [inline]
 migrate_pages+0x1f4e/0x34a0 mm/migrate.c:1493
 compact_zone+0x2c43/0x4260 mm/compaction.c:2424
 proactive_compact_node mm/compaction.c:2673 [inline]
 kcompactd+0x1403/0x1ff0 mm/compaction.c:2983
 kthread+0x42e/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/30 03:28 linux-5.15.y 28c35638ec51 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: rcu detected stall in kcompactd
2026/08/29 05:06 linux-5.15.y 28c35638ec51 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: rcu detected stall in kcompactd
* Struck through repros no longer work on HEAD.