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: 120d, last: 1d13h
▶ ▼ 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 795d 845d 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 1 250 1d22h 767d 0/29 upstream: reported on 2024/08/12 12:28
linux-6.6 INFO: rcu detected stall in kcov_close 1 1 271d 271d 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 845d 845d 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 678d 744d 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): P8729/1:b..l P5770/1:b..l
rcu: 	(detected by 0, t=10502 jiffies, g=32313, q=324 ncpus=1)
task:syz-executor    state:R  running task     stack:24360 pid:5770  ppid:5762   flags:0x00004002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5382 [inline]
 __schedule+0x15ae/0x4660 kernel/sched/core.c:6701
 preempt_schedule_irq+0xbf/0x150 kernel/sched/core.c:7011
 irqentry_exit+0x67/0x70 kernel/entry/common.c:441
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:stack_trace_consume_entry+0x7/0x270 kernel/stacktrace.c:83
Code: 00 48 3b 4c 24 78 75 09 48 8d 65 f0 5b 41 5e 5d c3 e8 dd 22 1b 09 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 f3 0f 1e fa 55 41 57 <41> 56 41 55 41 54 53 48 83 ec 18 48 ba 00 00 00 00 00 fc ff df 4c
RSP: 0018:ffffc90003db77f0 EFLAGS: 00000286
RAX: ffffffff8133205a RBX: ffffc90003db78c0 RCX: ffff88801bf63c00
RDX: 0000000000000000 RSI: ffffffff81d3be17 RDI: ffffc90003db78c0
RBP: ffffc90003db7890 R08: ffff88801bf63c00 R09: 0000000000000003
R10: 0000000000000004 R11: 0000000000000000 R12: ffffffff81d3be17
R13: 1ffff110037ec82f R14: ffffffff81762710 R15: ffffc90003db7808
 arch_stack_walk+0x138/0x190 arch/x86/kernel/stacktrace.c:27
 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:2899
 kcov_put kernel/kcov.c:440 [inline]
 kcov_close+0x2b/0x50 kernel/kcov.c:536
 __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
 __do_sys_exit_group kernel/exit.c:1043 [inline]
 __se_sys_exit_group kernel/exit.c:1041 [inline]
 __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1041
 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: 0033:0x7f9841d9e159
RSP: 002b:00007ffdc6481d88 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007f9841d9e159
RDX: 00007f9841dcb4d7 RSI: 0000000000000004 RDI: 0000000000000001
RBP: 00007f98420267b8 R08: 0000000000000000 R09: 0000000000000003
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000008
R13: 0000000000000003 R14: 00007ffdc6481fe8 R15: 0000000000000000
 </TASK>
task:syz-executor    state:R  running task     stack:27560 pid:8729  ppid:5782   flags:0x00004002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5382 [inline]
 __schedule+0x15ae/0x4660 kernel/sched/core.c:6701
 preempt_schedule_common+0x82/0xc0 kernel/sched/core.c:6868
 preempt_schedule+0xc0/0xd0 kernel/sched/core.c:6892
 preempt_schedule_thunk+0x1a/0x30 arch/x86/entry/thunk_64.S:45
 unwind_next_frame+0x201c/0x2990 arch/x86/kernel/unwind_orc.c:672
 arch_stack_walk+0x144/0x190 arch/x86/kernel/stacktrace.c:25
 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
 __slab_free+0x35a/0x400 mm/slub.c:3736
 qlink_free mm/kasan/quarantine.c:166 [inline]
 qlist_free_all+0x75/0xd0 mm/kasan/quarantine.c:185
 kasan_quarantine_reduce+0x143/0x160 mm/kasan/quarantine.c:292
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:306
 kasan_slab_alloc include/linux/kasan.h:188 [inline]
 slab_post_alloc_hook+0x6a/0x4d0 mm/slab.h:770
 slab_alloc_node mm/slub.c:3495 [inline]
 __kmem_cache_alloc_node+0x194/0x250 mm/slub.c:3534
 __do_kmalloc_node mm/slab_common.c:1006 [inline]
 __kmalloc+0xa7/0x240 mm/slab_common.c:1020
 kmalloc include/linux/slab.h:604 [inline]
 kzalloc include/linux/slab.h:721 [inline]
 tomoyo_encode2 security/tomoyo/realpath.c:45 [inline]
 tomoyo_encode+0x2ad/0x570 security/tomoyo/realpath.c:80
 tomoyo_path_perm+0x31a/0x560 security/tomoyo/file.c:831
 tomoyo_path_symlink+0xac/0xf0 security/tomoyo/tomoyo.c:211
 security_path_symlink+0xe0/0x130 security/security.c:1823
 do_symlinkat+0x110/0x400 fs/namei.c:4552
 __do_sys_symlinkat fs/namei.c:4570 [inline]
 __se_sys_symlinkat fs/namei.c:4567 [inline]
 __x64_sys_symlinkat+0x99/0xb0 fs/namei.c:4567
 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: 0033:0x7f254879d217
RSP: 002b:00007ffd31f3e468 EFLAGS: 00000202 ORIG_RAX: 000000000000010a
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f254879d217
RDX: 00007f2548836024 RSI: 00000000ffffff9c RDI: 00007ffd31f3e500
RBP: 00007ffd31f3e4ac R08: 0000000000000001 R09: 00000000ffffffff
R10: 0000000000000000 R11: 0000000000000202 R12: 00000000000000de
R13: 00000000000927c0 R14: 0000000000042866 R15: 00007ffd31f3e500
 </TASK>
rcu: rcu_preempt kthread starved for 2291 jiffies! g32313 f0x0 RCU_GP_WAIT_FQS(5) ->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:25960 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: 0 PID: 3388 Comm: kworker/R-bat_e Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Workqueue: bat_events batadv_tt_purge
RIP: 0010:deref_stack_reg+0x1bf/0x230 arch/x86/kernel/unwind_orc.c:406
Code: 97 a9 4b 00 49 bf 00 00 00 00 00 fc ff df 48 89 ef e8 b5 07 00 00 49 89 c6 48 8b 5c 24 10 48 89 d8 48 c1 e8 03 42 80 3c 38 00 <74> 08 48 89 df e8 27 36 a4 00 4c 89 33 b0 01 eb 0e e8 5b a9 4b 00
RSP: 0018:ffffc90000006c68 EFLAGS: 00000246
RAX: 1ffff92000000db9 RBX: ffffc90000006dc8 RCX: ffff88802d958000
RDX: 0000000000000100 RSI: 0000000000000001 RDI: ffffc9000cd47f20
RBP: ffffc9000cd47f20 R08: ffff88802d958000 R09: 0000000000000003
R10: 0000000000000004 R11: 0000000000000100 R12: ffffc9000cd48000
R13: 1ffff92000000db3 R14: 0000000000000000 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f015d52cfc9 CR3: 000000002e50c000 CR4: 00000000003506f0
Call Trace:
 <IRQ>
 unwind_next_frame+0x1781/0x2990 arch/x86/kernel/unwind_orc.c:648
 arch_stack_walk+0x144/0x190 arch/x86/kernel/stacktrace.c:25
 stack_trace_save+0xaa/0x100 kernel/stacktrace.c:122
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4e/0x70 mm/kasan/common.c:53
 __kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:329
 kasan_slab_alloc include/linux/kasan.h:188 [inline]
 slab_post_alloc_hook+0x6a/0x4d0 mm/slab.h:770
 slab_alloc_node mm/slub.c:3495 [inline]
 kmem_cache_alloc_node+0x1af/0x310 mm/slub.c:3540
 kmalloc_reserve+0x95/0x240 net/core/skbuff.c:562
 __alloc_skb+0x138/0x2c0 net/core/skbuff.c:653
 alloc_skb include/linux/skbuff.h:1316 [inline]
 synproxy_send_client_synack+0x170/0xda0 net/netfilter/nf_synproxy_core.c:464
 nft_synproxy_eval_v4+0x363/0x4e0 net/netfilter/nft_synproxy.c:58
 nft_synproxy_do_eval+0x332/0x550 net/netfilter/nft_synproxy.c:140
 expr_call_ops_eval net/netfilter/nf_tables_core.c:240 [inline]
 nft_do_chain+0x44b/0x1620 net/netfilter/nf_tables_core.c:288
 nft_do_chain_inet+0x29b/0x380 net/netfilter/nft_chain_filter.c:161
 nf_hook_entry_hookfn include/linux/netfilter.h:144 [inline]
 nf_hook_slow+0xbd/0x200 net/netfilter/core.c:626
 nf_hook include/linux/netfilter.h:259 [inline]
 NF_HOOK+0x21d/0x3b0 include/linux/netfilter.h:302
 NF_HOOK+0x32d/0x3b0 include/linux/netfilter.h:304
 __netif_receive_skb_one_core net/core/dev.c:5670 [inline]
 __netif_receive_skb+0xcc/0x290 net/core/dev.c:5784
 process_backlog+0x380/0x710 net/core/dev.c:6112
 __napi_poll+0xbb/0x460 net/core/dev.c:6674
 napi_poll net/core/dev.c:6741 [inline]
 net_rx_action+0x65f/0xcc0 net/core/dev.c:6877
 handle_softirqs+0x27d/0x820 kernel/softirq.c:578
 do_softirq+0xfa/0x1a0 kernel/softirq.c:479
 </IRQ>
 <TASK>
 __local_bh_enable_ip+0x184/0x1c0 kernel/softirq.c:406
 spin_unlock_bh include/linux/spinlock.h:396 [inline]
 batadv_tt_global_purge net/batman-adv/translation-table.c:2359 [inline]
 batadv_tt_purge+0x4b5/0xa20 net/batman-adv/translation-table.c:3633
 process_one_work kernel/workqueue.c:2657 [inline]
 process_scheduled_works+0xa60/0x1600 kernel/workqueue.c:2734
 rescuer_thread+0x71e/0x1080 kernel/workqueue.c:2931
 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 (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/17 08:39 linux-6.6.y 79643295eba1 95928915 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan INFO: rcu detected stall in kcov_close
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.