INFO: rcu detected stall in sendfile64 (2)

Status: upstream: reported C repro on 2026/07/04 16:00
Bug presence: origin:upstream
[Documentation on labels]
Reported-by: syzbot+f82981cd00f7429e4c9b@syzkaller.appspotmail.com
First crash: 34d, last: 13h37m
Fix bisection: the issue occurs on the latest tested release (bisect log)
  
▶ ▼ Bug presence (1)
Date Name Commit Repro Result
2026/07/17 upstream (ToT) af5e34a41cd6 C [report] INFO: rcu detected stall in worker_thread
▶ ▼ Similar bugs (17)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.6 INFO: rcu detected stall in sendfile64 origin:upstream 1 syz, C 2 5d19h 59d 0/2 upstream: reported C repro on 2026/06/10 03:23
linux-4.14 INFO: rcu detected stall in sendfile64 1 1 2675d 2675d 0/1 auto-closed as invalid on 2019/10/08 13:45
linux-5.15 INFO: rcu detected stall in sendfile64 1 1 273d 273d 0/3 auto-obsoleted due to no activity on 2026/02/15 23:07
linux-4.14 INFO: rcu detected stall in sendfile64 (2) 1 3 2193d 2347d 0/1 auto-closed as invalid on 2020/12/03 20:18
upstream INFO: rcu detected stall in sendfile64 prio:high mm 1 41 5d14h 174d 0/29 upstream: reported on 2026/02/14 22:22
upstream INFO: rcu detected stall in sys_sendfile64 (3) mm 1 2 1564d 1565d 0/29 auto-closed as invalid on 2022/06/25 08:10
upstream INFO: rcu detected stall in sys_sendfile64 (4) net 1 1 1305d 1305d 0/29 auto-obsoleted due to no activity on 2023/04/18 07:19
upstream INFO: rcu detected stall in sys_sendfile64 (6) fs mm 1 6 651d 812d 0/29 auto-obsoleted due to no activity on 2025/01/24 02:27
linux-5.15 INFO: rcu detected stall in sys_sendfile64 (2) 1 1 626d 626d 0/3 auto-obsoleted due to no activity on 2025/02/27 23:01
upstream INFO: rcu detected stall in sys_sendfile64 lsm 1 syz, C 4 2789d 2788d 0/29 closed as invalid on 2018/12/19 10:12
upstream INFO: rcu detected stall in sys_sendfile64 (2) 1 syz, C done error 100 1674d 2757d 0/29 closed as invalid on 2022/02/08 10:47
linux-4.19 INFO: rcu detected stall in sys_sendfile64 (2) 1 3 2333d 2385d 0/1 auto-closed as invalid on 2020/07/16 06:45
upstream INFO: rcu detected stall in sys_sendfile64 (7) mm 1 1 547d 547d 0/29 auto-obsoleted due to no activity on 2025/05/07 22:38
linux-6.1 INFO: rcu detected stall in sys_sendfile64 1 1 1179d 1179d 0/3 auto-obsoleted due to no activity on 2023/08/24 12:36
upstream INFO: rcu detected stall in sys_sendfile64 (5) fs 1 1 996d 996d 0/29 auto-obsoleted due to no activity on 2024/01/14 10:13
linux-4.19 INFO: rcu detected stall in sys_sendfile64 1 1 2667d 2667d 0/1 auto-closed as invalid on 2019/10/16 04:09
linux-5.15 INFO: rcu detected stall in sys_sendfile64 1 1 743d 743d 0/3 auto-obsoleted due to no activity on 2024/11/03 00:47
▶ ▼ Last patch testing requests (2)
Created Duration User Patch Repo Result
2026/07/19 14:14 23m retest repro linux-5.15.y report log
2026/07/19 14:14 21m 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): P4284/1:b..l
	(detected by 1, t=10502 jiffies, g=6933, q=39)
task:kworker/1:6     state:R  running task     stack:25552 pid: 4284 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_common_interrupt+0x22/0x40 arch/x86/include/asm/idtentry.h:667
RIP: 0010:seqcount_lockdep_reader_access+0x196/0x1d0 include/linux/seqlock.h:106
Code: f9 4d 85 e4 75 16 e8 e9 e4 51 f9 eb 15 e8 e2 e4 51 f9 e8 bd 08 98 01 4d 85 e4 74 ea e8 d3 e4 51 f9 fb 48 c7 04 24 0e 36 e0 45 <4b> c7 04 3e 00 00 00 00 43 c7 44 3e 08 00 00 00 00 65 48 8b 04 25
RSP: 0018:ffffc900034dfa20 EFLAGS: 00000293
RAX: ffffffff88270dcd RBX: 0000000000000000 RCX: ffff888028f19dc0
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc900034dfad0 R08: ffffffff901e915f R09: 1ffffffff203d22b
R10: dffffc0000000000 R11: fffffbfff203d22c R12: 0000000000000200
R13: dffffc0000000000 R14: 1ffff9200069bf44 R15: dffffc0000000000
 nf_conntrack_get_ht include/net/netfilter/nf_conntrack.h:338 [inline]
 gc_worker+0x2e5/0x13d0 net/netfilter/nf_conntrack_core.c:1472
 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 10527 jiffies! g6933 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:27872 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: 4382 Comm: syz.1.18 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:deref_stack_reg+0xa/0x120 arch/x86/kernel/unwind_orc.c:356
Code: 89 f1 80 e1 07 38 c1 0f 8c db f4 ff ff 4c 89 f7 e8 cb e5 88 00 e9 ce f4 ff ff 66 0f 1f 44 00 00 55 41 57 41 56 41 55 41 54 53 <48> 89 d3 49 89 f6 49 89 ff 49 bc 00 00 00 00 00 fc ff df 48 83 c7
RSP: 0018:ffffc90002f6f318 EFLAGS: 00000287
RAX: fffffffffffffff0 RBX: ffffc90002f6f3e8 RCX: 0000000000000000
RDX: ffffc90002f6f428 RSI: ffffc90002f6fa90 RDI: ffffc90002f6f3e8
RBP: dffffc0000000000 R08: ffffc90002f6fa90 R09: ffffc90002f6f438
R10: dffffc0000000000 R11: fffff520005ede89 R12: ffffffff8e11bfb3
R13: 1ffffffff1c237f6 R14: ffffc90002f6f41d R15: ffffffff8e11bfb2
 unwind_next_frame+0x10bb/0x1cf0 arch/x86/kernel/unwind_orc.c:-1
 arch_stack_walk+0x10c/0x140 arch/x86/kernel/stacktrace.c:25
 stack_trace_save+0xa6/0xf0 kernel/stacktrace.c:122
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:46
 kasan_set_free_info+0x1f/0x40 mm/kasan/generic.c:360
 ____kasan_slab_free+0xd5/0x110 mm/kasan/common.c:366
 kasan_slab_free include/linux/kasan.h:230 [inline]
 slab_free_hook mm/slub.c:1710 [inline]
 slab_free_freelist_hook+0xec/0x170 mm/slub.c:1736
 slab_free mm/slub.c:3504 [inline]
 kfree+0xef/0x2a0 mm/slub.c:4564
 iter_file_splice_write+0xb3e/0xcf0 fs/splice.c:717
 do_splice_from fs/splice.c:767 [inline]
 direct_splice_actor+0xe1/0x130 fs/splice.c:956
 splice_direct_to_actor+0x4e8/0xc00 fs/splice.c:902
 do_splice_direct+0x1d4/0x2f0 fs/splice.c:1008
 do_sendfile+0x524/0xe30 fs/read_write.c:1249
 __do_sys_sendfile64 fs/read_write.c:1317 [inline]
 __se_sys_sendfile64+0x141/0x1a0 fs/read_write.c:1303
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f4597761e59
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:00007ffc9fb70f58 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007f45979e9fa0 RCX: 00007f4597761e59
RDX: 0000000000000000 RSI: 0000000000000006 RDI: 0000000000000007
RBP: 00007f45977f7e6f R08: 0000000000000000 R09: 0000000000000000
R10: 000000007fffffff R11: 0000000000000246 R12: 0000000000000000
R13: 00007f45979e9fac R14: 00007f45979e9fa0 R15: 00007f45979e9fa0
 </TASK>

Crashes (5):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/07/05 12:37 linux-5.15.y c86c4726e7f0 fcece630 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in sendfile64
2026/07/05 05:54 linux-5.15.y c86c4726e7f0 fcece630 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in sendfile64
2026/08/07 13:51 linux-5.15.y aabd761612db e4ef95d6 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in sendfile64
2026/07/04 16:03 linux-5.15.y c86c4726e7f0 fcece630 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in sendfile64
2026/07/04 16:00 linux-5.15.y c86c4726e7f0 fcece630 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in sendfile64
* Struck through repros no longer work on HEAD.