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: 101d, last: 10d
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 inconclusive 2 72d 125d 0/2 upstream: reported C repro on 2026/06/10 03:23
linux-4.14 INFO: rcu detected stall in sendfile64 1 1 2742d 2742d 0/1 auto-closed as invalid on 2019/10/08 13:45
linux-5.15 INFO: rcu detected stall in sendfile64 1 1 340d 340d 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 2260d 2414d 0/1 auto-closed as invalid on 2020/12/03 20:18
upstream INFO: rcu detected stall in sendfile64 prio:high mm 1 42 35d 241d 0/29 upstream: reported on 2026/02/14 22:22
upstream INFO: rcu detected stall in sys_sendfile64 (3) mm 1 2 1631d 1631d 0/29 auto-closed as invalid on 2022/06/25 08:10
upstream INFO: rcu detected stall in sys_sendfile64 (4) net 1 1 1372d 1372d 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 717d 879d 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 693d 693d 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 2855d 2855d 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 1741d 2824d 0/29 closed as invalid on 2022/02/08 10:47
linux-4.19 INFO: rcu detected stall in sys_sendfile64 (2) 1 3 2400d 2452d 0/1 auto-closed as invalid on 2020/07/16 06:45
upstream INFO: rcu detected stall in sys_sendfile64 (7) mm 1 1 614d 614d 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 1246d 1246d 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 1063d 1063d 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 2734d 2734d 0/1 auto-closed as invalid on 2019/10/16 04:09
linux-5.15 INFO: rcu detected stall in sys_sendfile64 1 1 809d 809d 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=97b/1/0x4000000000000000 softirq=6836/6836 fqs=74 
	(t=10502 jiffies g=7389 q=1950)
rcu: rcu_preempt kthread starved for 10347 jiffies! g7389 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:27520 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:
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 4363 Comm: syz.1.18 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:check_preemption_disabled+0x47/0x110 lib/smp_processor_id.c:55
Code: 40 76 65 8b 0d a2 2a 41 76 f7 c1 ff ff ff 7f 74 1f 65 48 8b 0c 25 28 00 00 00 48 3b 4c 24 08 0f 85 c4 00 00 00 48 83 c4 10 5b <41> 5e 41 5f 5d c3 48 c7 04 24 00 00 00 00 9c 8f 04 24 f7 04 24 00
RSP: 0018:ffffc90003d5f9e0 EFLAGS: 00000086
RAX: 0000000000000001 RBX: ffff88801d948000 RCX: bc98a29e55374600
RDX: 0000000000000000 RSI: ffffffff8a2b39e0 RDI: ffffffff8a7a48c0
RBP: ffffc90003d5fb10 R08: ffffffff8d8b1eef R09: 1ffffffff1b163dd
R10: dffffc0000000000 R11: fffffbfff1b163de R12: 1ffff920007abf4c
R13: dffffc0000000000 R14: ffff88801d948aec R15: 0000000000000246
FS:  0000555579350500(0000) GS:ffff8880b9100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000000 CR3: 0000000073045000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 lockdep_recursion_inc kernel/locking/lockdep.c:431 [inline]
 lock_release+0x15d/0x8a0 kernel/locking/lockdep.c:5644
 __copy_from_user include/linux/uaccess.h:109 [inline]
 check_xstate_in_sigframe arch/x86/kernel/fpu/signal.c:33 [inline]
 __fpu_restore_sig arch/x86/kernel/fpu/signal.c:317 [inline]
 fpu__restore_sig+0x24f/0x10a0 arch/x86/kernel/fpu/signal.c:466
 restore_sigcontext arch/x86/kernel/signal.c:139 [inline]
 __ia32_sys_rt_sigreturn+0x5ef/0x750 arch/x86/kernel/signal.c:674
 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: 0033:0x7f20ea38b157
Code: 83 c8 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
RSP: 002b:00007ffdcd393d48 EFLAGS: 00000246
RAX: 0000000000000028 RBX: 00007f20ea612fa0 RCX: 00007f20ea38b159
RDX: 0000000000000000 RSI: 0000000000000006 RDI: 0000000000000005
RBP: 00007f20ea42206b R08: 0000000000000000 R09: 0000000000000000
R10: 0000020000023896 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f20ea612fac R14: 00007f20ea612fa0 R15: 00007f20ea612fa0
 </TASK>
NMI backtrace for cpu 0
CPU: 0 PID: 4362 Comm: syz.0.17 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:lock_acquire+0x208/0x400 kernel/locking/lockdep.c:5629
Code: f7 84 24 80 00 00 00 00 02 00 00 43 c6 44 3d 04 f8 0f 85 f1 00 00 00 41 f7 c6 00 02 00 00 74 01 fb 48 c7 44 24 60 0e 36 e0 45 <4b> c7 44 3d 00 00 00 00 00 43 c7 44 3d 08 00 00 00 00 65 48 8b 04
RSP: 0018:ffffc90003d8f6e0 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 75dbbfd7be9cd900
RDX: 0000000000000000 RSI: ffffffff8a2b3e80 RDI: ffffffff8a7a48c0
RBP: ffffc90003d8f7f8 R08: dffffc0000000000 R09: 1ffffffff203e218
R10: dffffc0000000000 R11: fffffbfff203e219 R12: ffffffff8c31ef60
R13: 1ffff920007b1ee8 R14: 0000000000000246 R15: dffffc0000000000
 rcu_lock_acquire+0x2a/0x30 include/linux/rcupdate.h:313
 rcu_read_lock include/linux/rcupdate.h:740 [inline]
 pfn_valid include/linux/mmzone.h:1522 [inline]
 __virt_addr_valid+0x17f/0x470 arch/x86/mm/physaddr.c:65
 check_heap_object mm/usercopy.c:228 [inline]
 __check_object_size+0xa8/0x410 mm/usercopy.c:286
 check_object_size include/linux/thread_info.h:199 [inline]
 check_copy_size include/linux/thread_info.h:232 [inline]
 copy_to_iter include/linux/uio.h:155 [inline]
 seq_read_iter+0xa7a/0xc50 fs/seq_file.c:281
 call_read_iter include/linux/fs.h:2173 [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: 0033:0x7f69a069c159
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:00007ffefd65f768 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007f69a0923fa0 RCX: 00007f69a069c159
RDX: 0000000000000000 RSI: 0000000000000006 RDI: 0000000000000005
RBP: 00007f69a073306b R08: 0000000000000000 R09: 0000000000000000
R10: 0000020000023896 R11: 0000000000000246 R12: 0000000000000000
sched: RT throttling activated
R13: 00007f69a0923fac R14: 00007f69a0923fa0 R15: 00007f69a0923fa0
 </TASK>

Crashes (28):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/27 11:15 linux-5.15.y 0248c33e835e a3c7249d .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in sendfile64
2026/08/22 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
2026/09/27 17:39 linux-5.15.y 0248c33e835e a3c7249d .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in sendfile64
2026/09/27 00:34 linux-5.15.y 0248c33e835e a3c7249d .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in sendfile64
2026/10/03 16:34 linux-5.15.y a051a4bf909f 57bbd979 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in sendfile64
2026/10/03 15:27 linux-5.15.y a051a4bf909f 57bbd979 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in sendfile64
2026/10/01 19:55 linux-5.15.y 0248c33e835e f5cdae2f .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in sendfile64
2026/10/01 10:28 linux-5.15.y 0248c33e835e 38f7f0d1 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in sendfile64
2026/09/19 14:51 linux-5.15.y 0248c33e835e 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in sendfile64
2026/09/05 08:53 linux-5.15.y 0996e0926f6b 4f7b22a0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in sendfile64
2026/08/29 11:05 linux-5.15.y 28c35638ec51 2f52988a .config console log report info [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.