INFO: rcu detected stall in kcov_close (2)

Status: upstream: reported on 2026/05/21 10:08
Reported-by: syzbot+5471950bb80340c1d274@syzkaller.appspotmail.com
First crash: 101d, last: 9d23h
▶ ▼ Similar bugs (5)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.1 INFO: rcu detected stall in kcov_close 1 6 776d 826d 0/3 auto-obsoleted due to no activity on 2024/10/23 16:14
upstream INFO: rcu detected stall in kcov_close prio:normal mm 1 245 7d02h 748d 0/29 upstream: reported on 2024/08/12 12:28
linux-6.6 INFO: rcu detected stall in kcov_close 1 1 252d 252d 0/2 auto-obsoleted due to no activity on 2026/03/31 08:37
linux-5.15 BUG: soft lockup in kcov_close 1 1 826d 826d 0/3 auto-obsoleted due to no activity on 2024/09/03 09:36
upstream INFO: task hung in release_tty (3) serial 1 3 660d 725d 0/29 auto-obsoleted due to no activity on 2025/02/07 03:06

Sample crash report:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	0-...!: (1 GPs behind) idle=d834/1/0x4000000000000000 softirq=32788/32789 fqs=2
rcu: 	(detected by 1, t=10502 jiffies, g=37501, q=1383 ncpus=2)
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 9584 Comm: syz.1.1395 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:advance_sched+0x96c/0xc70 net/sched/sch_taprio.c:997
Code: 24 08 49 89 84 24 50 01 00 00 48 89 df 4c 89 e3 48 8b 74 24 20 4c 89 e2 e8 11 03 00 00 48 8b 84 24 80 00 00 00 42 80 3c 30 00 <74> 0a 48 8b 7c 24 78 e8 88 97 28 f9 49 89 5f e8 48 8b bc 24 88 00
RSP: 0018:ffffc90000007c98 EFLAGS: 00000046
RAX: 1ffff1100b768a65 RBX: ffff88802b9c0c00 RCX: ffff888019343c00
RDX: 0000000000010000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: dffffc0000000000 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff52000000f84 R12: ffff88802b9c0c00
R13: ffff88805bb45000 R14: dffffc0000000000 R15: ffff88805bb45340
FS:  0000000000000000(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f6c1f55da08 CR3: 000000000cf32000 CR4: 00000000003506f0
Call Trace:
 <IRQ>
 __run_hrtimer kernel/time/hrtimer.c:1754 [inline]
 __hrtimer_run_queues+0x525/0xc10 kernel/time/hrtimer.c:1818
 hrtimer_interrupt+0x39d/0x980 kernel/time/hrtimer.c:1880
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1077 [inline]
 __sysvec_apic_timer_interrupt+0xfb/0x3b0 arch/x86/kernel/apic/apic.c:1094
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1088 [inline]
 sysvec_apic_timer_interrupt+0x9f/0xc0 arch/x86/kernel/apic/apic.c:1088
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:on_stack arch/x86/include/asm/stacktrace.h:55 [inline]
RIP: 0010:__unwind_start+0x501/0x730 arch/x86/kernel/unwind_orc.c:758
Code: 10 48 8b 44 24 08 48 83 c0 08 48 89 44 24 18 48 89 e8 48 c1 e8 03 48 89 04 24 4c 89 e8 48 c1 e8 03 48 89 44 24 20 48 8b 04 24 <42> 80 3c 38 00 74 08 48 89 ef e8 00 14 a4 00 4c 8b 65 00 48 8b 44
RSP: 0018:ffffc90004c57528 EFLAGS: 00000293
RAX: 1ffff9200098aeb2 RBX: ffffc90004c57588 RCX: ffff888019343c00
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: ffffc90004c57590 R08: ffff888019343c00 R09: 0000000000000003
R10: 0000000000000004 R11: 0000000000000000 R12: ffffc90004c57588
R13: ffffc90004c57598 R14: 1ffff9200098aeb1 R15: dffffc0000000000
 unwind_start arch/x86/include/asm/unwind.h:64 [inline]
 arch_stack_walk+0xf8/0x190 arch/x86/kernel/stacktrace.c:24
 stack_trace_save+0xaa/0x100 kernel/stacktrace.c:122
 save_stack+0x125/0x230 mm/page_owner.c:128
 __reset_page_owner+0x4e/0x190 mm/page_owner.c:149
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1182 [inline]
 free_unref_page_prepare+0x7d7/0x8f0 mm/page_alloc.c:2366
 free_unref_page+0x32/0x2e0 mm/page_alloc.c:2459
 vfree+0x1a7/0x340 mm/vmalloc.c:2868
 kcov_put kernel/kcov.c:438 [inline]
 kcov_close+0x2b/0x50 kernel/kcov.c:534
 __fput+0x221/0x940 fs/file_table.c:418
 task_work_run+0x1d4/0x260 kernel/task_work.c:245
 exit_task_work include/linux/task_work.h:43 [inline]
 do_exit+0x986/0x2530 kernel/exit.c:890
 do_group_exit+0x22d/0x2f0 kernel/exit.c:1032
 get_signal+0x12a6/0x1390 kernel/signal.c:2911
 arch_do_signal_or_restart+0xc2/0x7b0 arch/x86/kernel/signal.c:310
 exit_to_user_mode_loop+0x70/0x110 kernel/entry/common.c:174
 exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:210
 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
 syscall_exit_to_user_mode+0x1a/0x50 kernel/entry/common.c:302
 do_syscall_64+0x61/0xb0 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7ff24575e90e
Code: Unable to access opcode bytes at 0x7ff24575e8e4.
RSP: 002b:00007ffd3e68f968 EFLAGS: 00000246 ORIG_RAX: 00000000000000e6
RAX: 0000000000000000 RBX: 0000555575ff3500 RCX: 00007ff24575e90e
RDX: 00007ffd3e68f9c0 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00007ff245a27da0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000003ae61
R13: 00007ff245a2609c R14: 000000000003ac54 R15: 00007ff245a26090
 </TASK>
rcu: rcu_preempt kthread starved for 10490 jiffies! g37501 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:26504 pid:17    ppid:2      flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5382 [inline]
 __schedule+0x15ae/0x4660 kernel/sched/core.c:6701
 schedule+0xbd/0x170 kernel/sched/core.c:6775
 schedule_timeout+0x188/0x2d0 kernel/time/timer.c:2168
 rcu_gp_fqs_loop+0x30d/0x1590 kernel/rcu/tree.c:1667
 rcu_gp_kthread+0x9d/0x3b0 kernel/rcu/tree.c:1866
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
CPU: 1 PID: 3474 Comm: kworker/u4:10 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Workqueue: events_unbound toggle_allocation_gate
RIP: 0010:csd_lock_wait kernel/smp.c:311 [inline]
RIP: 0010:smp_call_function_many_cond+0xd85/0x1190 kernel/smp.c:855
Code: 45 8b 34 24 44 89 f6 83 e6 01 31 ff e8 14 01 0b 00 41 83 e6 01 49 be 00 00 00 00 00 fc ff df 75 07 e8 4f fd 0a 00 eb 38 f3 90 <42> 0f b6 04 33 84 c0 75 11 41 f7 04 24 01 00 00 00 74 1e e8 33 fd
RSP: 0018:ffffc9000cb1f780 EFLAGS: 00000293
RAX: ffffffff817c753d RBX: 1ffff110171c87ad RCX: ffff88802e0b9e00
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: ffffc9000cb1f900 R08: ffffffff911ee507 R09: 1ffffffff223dca0
R10: dffffc0000000000 R11: fffffbfff223dca1 R12: ffff8880b8e43d68
R13: ffff8880b8f3d3c0 R14: dffffc0000000000 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fbb6c793000 CR3: 000000000cf32000 CR4: 00000000003506e0
Call Trace:
 <TASK>
 on_each_cpu_cond_mask+0x3f/0x80 kernel/smp.c:1022
 on_each_cpu include/linux/smp.h:71 [inline]
 text_poke_sync arch/x86/kernel/alternative.c:2222 [inline]
 text_poke_bp_batch+0x31e/0x980 arch/x86/kernel/alternative.c:2432
 text_poke_flush arch/x86/kernel/alternative.c:2623 [inline]
 text_poke_finish+0x30/0x50 arch/x86/kernel/alternative.c:2630
 arch_jump_label_transform_apply+0x1c/0x30 arch/x86/kernel/jump_label.c:146
 static_key_enable_cpuslocked+0x123/0x240 kernel/jump_label.c:207
 static_key_enable+0x1a/0x20 kernel/jump_label.c:220
 toggle_allocation_gate+0xa8/0x260 mm/kfence/core.c:847
 process_one_work kernel/workqueue.c:2657 [inline]
 process_scheduled_works+0xa60/0x1600 kernel/workqueue.c:2734
 worker_thread+0xa5e/0xfe0 kernel/workqueue.c:2815
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
 </TASK>

Crashes (3):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/21 05:05 linux-6.6.y c610b395b0a5 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan INFO: rcu detected stall in kcov_close
2026/05/24 05:59 linux-6.6.y 0a40c6fbd105 c69befb3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan INFO: rcu detected stall in kcov_close
2026/05/21 10:07 linux-6.6.y eac8889a3a1c 41b8c833 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan INFO: rcu detected stall in kcov_close
* Struck through repros no longer work on HEAD.