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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: 24d, last: 21d
▶ ▼ 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 699d 749d 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 1 217 21h43m 671d 0/29 upstream: reported on 2024/08/12 12:28
linux-6.6 INFO: rcu detected stall in kcov_close 1 1 175d 175d 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 749d 749d 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 582d 648d 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: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P6503/1:b..l P5764/1:b..l P8214/1:b..l
rcu: 	(detected by 1, t=10503 jiffies, g=62277, q=163 ncpus=2)
task:syz-executor    state:R  running task     stack:21736 pid:8214  ppid:1      flags:0x00004006
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5381 [inline]
 __schedule+0x1553/0x45a0 kernel/sched/core.c:6700
 preempt_schedule_irq+0xbf/0x150 kernel/sched/core.c:7010
 irqentry_exit+0x67/0x70 kernel/entry/common.c:438
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:is_bpf_text_address+0xd/0x2a0 kernel/bpf/core.c:738
Code: 48 83 c4 28 5b 41 5c 41 5d 41 5e 41 5f 5d c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 66 0f 1f 00 55 41 57 41 56 41 55 41 54 <53> 48 83 ec 10 49 89 fe e8 96 a9 f2 ff e8 b1 34 dd ff 48 8d 05 00
RSP: 0000:ffffc90004a7f500 EFLAGS: 00000246
RAX: 0000000000000000 RBX: 00007f737d59bf47 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff8b1c9a00 RDI: 00007f737d59bf47
RBP: 0000000000000001 R08: ffff888028bc1e00 R09: 0000000000000003
R10: 0000000000000004 R11: 0000000000000000 R12: ffffffff8aa000d0
R13: 1ffff1100517846e R14: 0000000000000001 R15: 1ffff9200094feba
 kernel_text_address+0xa0/0xd0 kernel/extable.c:125
 __kernel_text_address+0xd/0x30 kernel/extable.c:79
 unwind_get_return_address+0x5d/0xc0 arch/x86/kernel/unwind_orc.c:369
 arch_stack_walk+0x11d/0x190 arch/x86/kernel/stacktrace.c:26
 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:1181 [inline]
 free_unref_page_prepare+0x7b2/0x8c0 mm/page_alloc.c:2365
 free_unref_page+0x32/0x2e0 mm/page_alloc.c:2458
 vfree+0x1a6/0x320 mm/vmalloc.c:2868
 kcov_put kernel/kcov.c:438 [inline]
 kcov_close+0x2b/0x50 kernel/kcov.c:534
 __fput+0x234/0x970 fs/file_table.c:384
 task_work_run+0x1d4/0x260 kernel/task_work.c:245
 exit_task_work include/linux/task_work.h:43 [inline]
 do_exit+0x95a/0x2460 kernel/exit.c:884
 do_group_exit+0x21b/0x2d0 kernel/exit.c:1026
 get_signal+0x12fc/0x13f0 kernel/signal.c:2902
 arch_do_signal_or_restart+0xc2/0x800 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: 0033:0x7f737d59bf47
RSP: 002b:00007ffe331f8438 EFLAGS: 00000206 ORIG_RAX: 0000000000000057
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 00007f737d59bf47
RDX: 00007ffe331f8460 RSI: 00007ffe331f84f0 RDI: 00007ffe331f84f0
RBP: 00007ffe331f84f0 R08: 00007ffe331f94f0 R09: 00000000ffffffff
R10: 0000000000000100 R11: 0000000000000206 R12: 00007ffe331f9580
R13: 00007f737d6321ca R14: 00000000001045fa R15: 00007ffe331f95c0
 </TASK>
task:kworker/0:3     state:R  running task     stack:25008 pid:5764  ppid:2      flags:0x00004000
Workqueue: events_power_efficient gc_worker
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5381 [inline]
 __schedule+0x1553/0x45a0 kernel/sched/core.c:6700
 preempt_schedule_irq+0xbf/0x150 kernel/sched/core.c:7010
 irqentry_exit+0x67/0x70 kernel/entry/common.c:438
 asm_sysvec_reschedule_ipi+0x1a/0x20 arch/x86/include/asm/idtentry.h:692
RIP: 0010:lock_acquire+0x208/0x420 kernel/locking/lockdep.c:5758
Code: f7 84 24 80 00 00 00 00 02 00 00 43 c6 44 3c 04 f8 0f 85 f0 00 00 00 41 f7 c6 00 02 00 00 74 01 fb 48 c7 44 24 60 0e 36 e0 45 <4b> c7 04 3c 00 00 00 00 43 c7 44 3c 08 00 00 00 00 65 48 8b 04 25
RSP: 0018:ffffc90003d57940 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 38bf5e1b33bc4100
RDX: 0000000000000000 RSI: ffffffff8acadd60 RDI: ffffffff8b1c9a20
RBP: ffffc90003d57a48 R08: dffffc0000000000 R09: 1ffffffff22392a0
R10: dffffc0000000000 R11: fffffbfff22392a1 R12: 1ffff920007aaf34
R13: ffffffff8d132120 R14: 0000000000000246 R15: dffffc0000000000
 rcu_lock_acquire include/linux/rcupdate.h:334 [inline]
 rcu_read_lock include/linux/rcupdate.h:786 [inline]
 gc_worker+0x28d/0x1490 net/netfilter/nf_conntrack_core.c:1502
 process_one_work kernel/workqueue.c:2653 [inline]
 process_scheduled_works+0xa5d/0x15d0 kernel/workqueue.c:2730
 worker_thread+0xa55/0xfc0 kernel/workqueue.c:2811
 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>
task:syz-executor    state:R  running task     stack:21736 pid:6503  ppid:6491   flags:0x00004002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5381 [inline]
 __schedule+0x1553/0x45a0 kernel/sched/core.c:6700
 preempt_schedule_irq+0xbf/0x150 kernel/sched/core.c:7010
 irqentry_exit+0x67/0x70 kernel/entry/common.c:438
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:unwind_get_return_address+0x4b/0xc0 arch/x86/kernel/unwind_orc.c:369
Code: e8 03 42 0f b6 04 30 84 c0 75 6e 8b 2b 31 ff 89 ee e8 49 f9 4b 00 85 ed 74 4a 48 83 c3 48 49 89 df 49 c1 ef 03 43 80 3c 37 00 <74> 08 48 89 df e8 cb 34 a4 00 48 8b 3b e8 33 57 1e 00 89 c5 31 ff
RSP: 0000:ffffc90003dc73c0 EFLAGS: 00000246
RAX: ffffffff813b3657 RBX: ffffc90003dc7430 RCX: 0000000000000000
RDX: ffff88802b253c00 RSI: 0000000000000001 RDI: 0000000000000000
RBP: 0000000000000001 R08: ffff88802b253c00 R09: 0000000000000003
R10: 0000000000000004 R11: 0000000000000000 R12: ffffffff81bafbea
R13: 1ffff1100564a82e R14: dffffc0000000000 R15: 1ffff920007b8e86
 arch_stack_walk+0x11d/0x190 arch/x86/kernel/stacktrace.c:26
 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:1181 [inline]
 free_unref_page_prepare+0x7b2/0x8c0 mm/page_alloc.c:2365
 free_unref_page_list+0xbe/0x860 mm/page_alloc.c:2504
 release_pages+0x1f7a/0x2200 mm/swap.c:1022
 __folio_batch_release+0x71/0xe0 mm/swap.c:1042
 folio_batch_release include/linux/pagevec.h:83 [inline]
 shmem_undo_range+0x630/0x1b20 mm/shmem.c:1026
 shmem_truncate_range mm/shmem.c:1135 [inline]
 shmem_evict_inode+0x245/0x9e0 mm/shmem.c:1264
 evict+0x4ca/0x8d0 fs/inode.c:705
 do_unlinkat+0x38c/0x590 fs/namei.c:4406
 __do_sys_unlink fs/namei.c:4447 [inline]
 __se_sys_unlink fs/namei.c:4445 [inline]
 __x64_sys_unlink+0x49/0x50 fs/namei.c:4445
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f2e8c99bf47
RSP: 002b:00007ffc03a58c98 EFLAGS: 00000206 ORIG_RAX: 0000000000000057
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f2e8c99bf47
RDX: 00007ffc03a58cc0 RSI: 00007ffc03a58d50 RDI: 00007ffc03a58d50
RBP: 00007ffc03a58d50 R08: 00007ffc03a59d50 R09: 00000000ffffffff
R10: 0000000000000100 R11: 0000000000000206 R12: 00007ffc03a59de0
R13: 00007f2e8ca321ca R14: 0000000000106597 R15: 00007ffc03a59e20
 </TASK>
rcu: rcu_preempt kthread starved for 10290 jiffies! g62277 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:26920 pid:17    ppid:2      flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5381 [inline]
 __schedule+0x1553/0x45a0 kernel/sched/core.c:6700
 schedule+0xbd/0x170 kernel/sched/core.c:6774
 schedule_timeout+0x188/0x2d0 kernel/time/timer.c:2168
 rcu_gp_fqs_loop+0x313/0x1590 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: 0 Comm: swapper/1 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
RIP: 0010:pv_native_safe_halt+0xf/0x10 arch/x86/kernel/paravirt.c:148
Code: 68 20 02 c3 cc cc cc cc cc cc cc f3 0f 1e fa 0f 0b 66 2e 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 66 90 0f 00 2d 43 f4 40 00 fb f4 <c3> 66 0f 1f 00 55 41 57 41 56 41 54 53 50 8b 2f eb 2e 41 89 de 80
RSP: 0018:ffffc90000187de0 EFLAGS: 000002c2
RAX: 2c5c3930e72e8d00 RBX: ffffffff8162afbd RCX: 2c5c3930e72e8d00
RDX: 0000000000000001 RSI: ffffffff8acacbe0 RDI: ffffffff8b1c9a20
RBP: ffffc90000187f20 R08: ffff8880b8f36b2b R09: 1ffff110171e6d65
R10: dffffc0000000000 R11: ffffed10171e6d66 R12: 1ffff92000030fc8
R13: dffffc0000000000 R14: 1ffff110036cd780 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555556b8fa38 CR3: 000000001b795000 CR4: 00000000003506e0
Call Trace:
 <TASK>
 arch_safe_halt arch/x86/include/asm/paravirt.h:108 [inline]
 default_idle+0x13/0x20 arch/x86/kernel/process.c:753
 default_idle_call+0x6c/0xa0 kernel/sched/idle.c:97
 cpuidle_idle_call kernel/sched/idle.c:178 [inline]
 do_idle+0x33d/0x590 kernel/sched/idle.c:302
 cpu_startup_entry+0x43/0x60 kernel/sched/idle.c:401
 start_secondary+0xee/0xf0 arch/x86/kernel/smpboot.c:323
 secondary_startup_64_no_verify+0x179/0x17b
 </TASK>

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
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.