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: 53d, last: 1d16h
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 24d 77d 0/2 upstream: reported C repro on 2026/06/10 03:23
linux-4.14 INFO: rcu detected stall in sendfile64 1 1 2694d 2694d 0/1 auto-closed as invalid on 2019/10/08 13:45
linux-5.15 INFO: rcu detected stall in sendfile64 1 1 291d 291d 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 2212d 2366d 0/1 auto-closed as invalid on 2020/12/03 20:18
upstream INFO: rcu detected stall in sendfile64 prio:high mm 1 41 24d 193d 0/29 upstream: reported on 2026/02/14 22:22
upstream INFO: rcu detected stall in sys_sendfile64 (3) mm 1 2 1583d 1583d 0/29 auto-closed as invalid on 2022/06/25 08:10
upstream INFO: rcu detected stall in sys_sendfile64 (4) net 1 1 1324d 1324d 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 669d 830d 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 644d 644d 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 2807d 2807d 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 1693d 2776d 0/29 closed as invalid on 2022/02/08 10:47
linux-4.19 INFO: rcu detected stall in sys_sendfile64 (2) 1 3 2352d 2404d 0/1 auto-closed as invalid on 2020/07/16 06:45
upstream INFO: rcu detected stall in sys_sendfile64 (7) mm 1 1 566d 566d 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 1198d 1198d 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 1015d 1015d 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 2686d 2686d 0/1 auto-closed as invalid on 2019/10/16 04:09
linux-5.15 INFO: rcu detected stall in sys_sendfile64 1 1 761d 761d 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 self-detected stall on CPU
rcu: 	0-...!: (10500 ticks this GP) idle=bc3/1/0x4000000000000000 softirq=7324/7324 fqs=0 
	(t=10501 jiffies g=8029 q=8445)
rcu: rcu_preempt kthread timer wakeup didn't happen for 10501 jiffies! g8029 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402
rcu: 	Possible timer handling issue on cpu=0 timer-softirq=5354
rcu: rcu_preempt kthread starved for 10504 jiffies! g8029 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->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:I 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 0
CPU: 0 PID: 4392 Comm: syz.2.30 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_cpu_stall+0x31a/0x5f0 kernel/rcu/tree_stall.h:631
 check_cpu_stall kernel/rcu/tree_stall.h:727 [inline]
 rcu_pending kernel/rcu/tree.c:3936 [inline]
 rcu_sched_clock_irq+0x6ec/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:__sanitizer_cov_trace_pc+0x58/0x60 kernel/kcov.c:216
Code: 10 16 00 00 83 fa 02 75 21 48 8b 91 18 16 00 00 48 8b 32 48 8d 7e 01 8b 89 14 16 00 00 48 39 cf 73 08 48 89 44 f2 08 48 89 3a <c3> 0f 1f 80 00 00 00 00 48 8b 04 24 65 48 8b 0d c4 71 89 7e 65 8b
RSP: 0018:ffffc9000347f830 EFLAGS: 00000293
RAX: ffffffff812df354 RBX: fffffbfff144d0c0 RCX: ffff88802ccc1dc0
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000002
RBP: 000000000000dc00 R08: ffff88802ccc1dc0 R09: 0000000000000012
R10: 0000000000000012 R11: 0000000000000000 R12: ffffffff8a267200
R13: 00000000000000c9 R14: 0000000000000648 R15: ffff8880b9121460
 show_cpuinfo+0x554/0xd20 arch/x86/kernel/cpu/proc.c:106
 seq_read_iter+0x8af/0xc50 fs/seq_file.c:272
 call_read_iter include/linux/fs.h:2167 [inline]
 generic_file_splice_read+0x3ed/0x5f0 fs/splice.c:311
 do_splice_to fs/splice.c:807 [inline]
 splice_direct_to_actor+0x41f/0xc00 fs/splice.c:881
 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: 0033:0x7f421a6f80d9
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:00007ffd4d7091c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007f421a97ffa0 RCX: 00007f421a6f80d9
RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000003
RBP: 00007f421a78f024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000020000023896 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f421a97ffac R14: 00007f421a97ffa0 R15: 00007f421a97ffa0
 </TASK>
NMI backtrace for cpu 0
CPU: 0 PID: 4392 Comm: syz.2.30 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_dump_cpu_stacks+0x22d/0x380 kernel/rcu/tree_stall.h:349
 print_cpu_stall+0x31f/0x5f0 kernel/rcu/tree_stall.h:633
 check_cpu_stall kernel/rcu/tree_stall.h:727 [inline]
 rcu_pending kernel/rcu/tree.c:3936 [inline]
 rcu_sched_clock_irq+0x6ec/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:__sanitizer_cov_trace_pc+0x58/0x60 kernel/kcov.c:216
Code: 10 16 00 00 83 fa 02 75 21 48 8b 91 18 16 00 00 48 8b 32 48 8d 7e 01 8b 89 14 16 00 00 48 39 cf 73 08 48 89 44 f2 08 48 89 3a <c3> 0f 1f 80 00 00 00 00 48 8b 04 24 65 48 8b 0d c4 71 89 7e 65 8b
RSP: 0018:ffffc9000347f830 EFLAGS: 00000293
RAX: ffffffff812df354 RBX: fffffbfff144d0c0 RCX: ffff88802ccc1dc0
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000002
RBP: 000000000000dc00 R08: ffff88802ccc1dc0 R09: 0000000000000012
R10: 0000000000000012 R11: 0000000000000000 R12: ffffffff8a267200
R13: 00000000000000c9 R14: 0000000000000648 R15: ffff8880b9121460
 show_cpuinfo+0x554/0xd20 arch/x86/kernel/cpu/proc.c:106
 seq_read_iter+0x8af/0xc50 fs/seq_file.c:272
 call_read_iter include/linux/fs.h:2167 [inline]
 generic_file_splice_read+0x3ed/0x5f0 fs/splice.c:311
 do_splice_to fs/splice.c:807 [inline]
 splice_direct_to_actor+0x41f/0xc00 fs/splice.c:881
 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: 0033:0x7f421a6f80d9
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:00007ffd4d7091c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007f421a97ffa0 RCX: 00007f421a6f80d9
RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000003
RBP: 00007f421a78f024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000020000023896 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f421a97ffac R14: 00007f421a97ffa0 R15: 00007f421a97ffa0
 </TASK>

Crashes (18):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/22 03:09 linux-5.15.y 0eb903b5b519 1e72964b .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 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
2026/08/25 05:45 linux-5.15.y 945fa863f02c 614e416a .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in sendfile64
2026/08/24 06:03 linux-5.15.y 945fa863f02c 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in sendfile64
2026/08/21 22:58 linux-5.15.y 0eb903b5b519 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in sendfile64
2026/08/18 04:23 linux-5.15.y aabd761612db 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in sendfile64
2026/08/14 19:52 linux-5.15.y aabd761612db 6f9b3e89 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in sendfile64
2026/08/13 23:20 linux-5.15.y aabd761612db b13552fe .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in sendfile64
2026/08/13 23:19 linux-5.15.y aabd761612db b13552fe .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in sendfile64
2026/08/08 09:12 linux-5.15.y aabd761612db 5d63f80b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in sendfile64
2026/08/08 09:10 linux-5.15.y aabd761612db 5d63f80b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in sendfile64
2026/08/08 09:06 linux-5.15.y aabd761612db 5d63f80b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in sendfile64
2026/08/08 09:06 linux-5.15.y aabd761612db 5d63f80b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in sendfile64
2026/08/08 08:36 linux-5.15.y aabd761612db 5d63f80b .config console log report info [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.