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INFO: rcu detected stall in futex

Status: upstream: reported C repro on 2025/08/10 09:30
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+795c184c6744be404955@syzkaller.appspotmail.com
First crash: 15d, last: 3d15h
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2025/08/22 linux-6.6.y (ToT) bb9c90ab9c5a C [report] INFO: rcu detected stall in __fdget
2025/08/22 upstream (ToT) 3957a5720157 C Didn't crash
▶ ▼ Similar bugs (11)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: rcu detected stall in sys_futex (7) kernel 1 syz error 89 3d01h 427d 0/29 upstream: reported syz repro on 2024/06/24 16:48
linux-5.15 INFO: rcu detected stall in sys_futex (2) origin:lts-only 1 syz error 22 1d15h 446d 0/3 upstream: reported syz repro on 2024/06/05 16:49
upstream INFO: rcu detected stall in futex kvm 1 1 1681d 1681d 0/29 auto-closed as invalid on 2021/04/17 19:46
linux-6.1 INFO: rcu detected stall in sys_futex origin:lts-only 1 syz done 19 112d 782d 0/3 upstream: reported syz repro on 2023/07/05 11:35
upstream INFO: rcu detected stall in sys_futex (3) mm 1 959 2056d 2105d 0/29 auto-closed as invalid on 2020/03/08 12:44
upstream INFO: rcu detected stall in sys_futex (2) kernel 1 6 2224d 2368d 0/29 auto-closed as invalid on 2019/10/25 14:11
upstream INFO: rcu detected stall in sys_futex (4) kernel 1 1 1305d 1305d 0/29 closed as invalid on 2022/02/08 10:00
upstream INFO: rcu detected stall in sys_futex kernel 1 1 2430d 2430d 0/29 closed as invalid on 2018/12/31 04:10
linux-5.15 INFO: rcu detected stall in sys_futex 1 4 602d 777d 0/3 auto-obsoleted due to no activity on 2024/04/10 17:08
upstream INFO: rcu detected stall in sys_futex (5) kernel 1 12 1036d 1281d 0/29 auto-obsoleted due to no activity on 2023/02/12 18:33
upstream INFO: rcu detected stall in sys_futex (6) kernel 1 10 605d 840d 0/29 auto-obsoleted due to no activity on 2024/03/29 00:57

Sample crash report:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	0-....: (1 GPs behind) idle=2c64/1/0x4000000000000000 softirq=12169/12170 fqs=5249
rcu: 	         hardirqs   softirqs   csw/system
rcu: 	 number: 17351194          0            0
rcu: 	cputime:     6424      46093            0   ==> 52500(ms)
rcu: 	(detected by 1, t=10502 jiffies, g=9269, q=548 ncpus=2)
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 5989 Comm: syz.0.30 Not tainted 6.6.102-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
RIP: 0010:bytes_is_nonzero mm/kasan/generic.c:85 [inline]
RIP: 0010:memory_is_nonzero mm/kasan/generic.c:102 [inline]
RIP: 0010:memory_is_poisoned_n mm/kasan/generic.c:127 [inline]
RIP: 0010:memory_is_poisoned mm/kasan/generic.c:159 [inline]
RIP: 0010:check_region_inline mm/kasan/generic.c:178 [inline]
RIP: 0010:kasan_check_range+0x89/0x290 mm/kasan/generic.c:187
Code: 00 fc ff df 4d 8d 34 19 4d 89 f4 4d 29 dc 49 83 fc 10 7f 29 4d 85 e4 0f 84 41 01 00 00 4c 89 cb 48 f7 d3 4c 01 fb 41 80 3b 00 <0f> 85 cc 01 00 00 49 ff c3 48 ff c3 75 ee e9 21 01 00 00 44 89 dd
RSP: 0018:ffffc900000071a8 EFLAGS: 00000046
RAX: 0000000000000001 RBX: ffffffffffffffff RCX: ffffffff81706455
RDX: 0000000000000000 RSI: 0000000000000008 RDI: ffffffff8e4a8828
RBP: ffffc900000072e0 R08: ffffffff8e4a882f R09: 1ffffffff1c95105
R10: dffffc0000000000 R11: fffffbfff1c95105 R12: 0000000000000001
R13: 0000000000000000 R14: fffffbfff1c95106 R15: 1ffffffff1c95105
FS:  00007fa6599a26c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000007df83000 CR4: 00000000003506f0
Call Trace:
 <IRQ>
 instrument_atomic_read include/linux/instrumented.h:68 [inline]
 _test_bit include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline]
 cpumask_test_cpu include/linux/cpumask.h:504 [inline]
 cpu_online include/linux/cpumask.h:1082 [inline]
 rcu_read_unlock_special+0x305/0x4c0 kernel/rcu/tree_plugin.h:664
 __rcu_read_unlock+0x7c/0xd0 kernel/rcu/tree_plugin.h:426
 rcu_read_unlock include/linux/rcupdate.h:818 [inline]
 __perf_event_output kernel/events/core.c:7983 [inline]
 perf_event_output_forward+0x2e6/0x3a0 kernel/events/core.c:7992
 __perf_event_overflow+0x447/0x630 kernel/events/core.c:9717
 perf_swevent_overflow kernel/events/core.c:9793 [inline]
 perf_swevent_event+0x2f5/0x5c0 kernel/events/core.c:-1
 perf_tp_event+0x4f9/0x13a0 kernel/events/core.c:10343
 perf_trace_run_bpf_submit+0xf4/0x1c0 kernel/events/core.c:10267
 perf_trace_preemptirq_template+0x281/0x340 include/trace/events/preemptirq.h:14
 trace_irq_enable+0xbf/0xe0 include/trace/events/preemptirq.h:40
 trace_hardirqs_on+0x18/0x40 kernel/trace/trace_preemptirq.c:56
 asm_sysvec_irq_work+0x1a/0x20 arch/x86/include/asm/idtentry.h:723
RIP: 0010:rcu_read_unlock_special+0x88/0x4c0 kernel/rcu/tree_plugin.h:682
Code: f1 f1 f1 00 f2 f2 f2 4a 89 04 2b 66 42 c7 44 2b 09 f3 f3 42 c6 44 2b 0b f3 65 44 8b 35 39 58 93 7e 41 f7 c6 00 00 f0 00 74 45 <48> c7 44 24 40 0e 36 e0 45 4a c7 04 2b 00 00 00 00 66 42 c7 44 2b
RSP: 0018:ffffc90000007a00 EFLAGS: 00000206
RAX: 2caa672456fd4f00 RBX: 1ffff92000000f48 RCX: 2caa672456fd4f00
RDX: dffffc0000000000 RSI: ffffffff8aaab9c0 RDI: ffffffff8afc66c0
RBP: ffffc90000007b00 R08: ffffffff8e4a882f R09: 1ffffffff1c95105
R10: dffffc0000000000 R11: fffffbfff1c95106 R12: ffffffff8cd35400
R13: dffffc0000000000 R14: 0000000000000246 R15: 0000000000000001
 __rcu_read_unlock+0x7c/0xd0 kernel/rcu/tree_plugin.h:426
 rcu_read_unlock include/linux/rcupdate.h:818 [inline]
 process_backlog+0x403/0x6e0 net/core/dev.c:6039
 __napi_poll+0xc0/0x460 net/core/dev.c:6600
 napi_poll net/core/dev.c:6667 [inline]
 net_rx_action+0x5ea/0xbf0 net/core/dev.c:6803
 handle_softirqs+0x280/0x820 kernel/softirq.c:578
 __do_softirq kernel/softirq.c:612 [inline]
 invoke_softirq kernel/softirq.c:452 [inline]
 __irq_exit_rcu+0xc7/0x190 kernel/softirq.c:661
 irq_exit_rcu+0x9/0x20 kernel/softirq.c:673
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1088 [inline]
 sysvec_apic_timer_interrupt+0xa4/0xc0 arch/x86/kernel/apic/apic.c:1088
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:preempt_schedule_irq+0xb0/0x140 kernel/sched/core.c:7009
Code: 44 24 20 f6 44 24 21 02 74 0b 0f 0b 48 f7 03 08 00 00 00 74 63 bf 01 00 00 00 e8 4b da e5 f6 e8 46 5f 16 f7 fb bf 01 00 00 00 <e8> db b5 ff ff 48 c7 44 24 40 00 00 00 00 9c 8f 44 24 40 8b 44 24
RSP: 0018:ffffc900034b7a00 EFLAGS: 00000286
RAX: 2caa672456fd4f00 RBX: 0000000000000000 RCX: 2caa672456fd4f00
RDX: dffffc0000000000 RSI: ffffffff8aaab9c0 RDI: 0000000000000001
RBP: ffffc900034b7ab0 R08: ffffffff8e4a882f R09: 1ffffffff1c95105
R10: dffffc0000000000 R11: fffffbfff1c95106 R12: 0000000000000000
R13: 0000000000000000 R14: dffffc0000000000 R15: 1ffff92000696f40
 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:try_to_wake_up+0x73f/0x1140 kernel/sched/core.c:4355
Code: 0f 1f 44 00 00 bf 01 00 00 00 e8 ec 5a ff ff 65 8b 05 0d aa a7 7e 85 c0 74 22 65 48 8b 04 25 28 00 00 00 48 3b 44 24 40 75 59 <44> 89 f0 48 83 c4 48 5b 41 5c 41 5d 41 5e 41 5f 5d c3 e8 ca 8b a4
RSP: 0018:ffffc900034b7b70 EFLAGS: 00000246
RAX: 2caa672456fd4f00 RBX: ffff8880b8e3d198 RCX: 0000000000000000
RDX: dffffc0000000000 RSI: ffffffff8aaab9c0 RDI: 00000000ffffffff
RBP: ffff88802d6e5a00 R08: ffffffff8e4a882f R09: 1ffffffff1c95105
R10: dffffc0000000000 R11: fffffbfff1c95106 R12: 0000000000000000
R13: dffffc0000000000 R14: 0000000000000001 R15: dffffc0000000000
 wake_up_process kernel/sched/core.c:4480 [inline]
 wake_up_q+0xb6/0x100 kernel/sched/core.c:1031
 futex_wake+0x40d/0x4b0 kernel/futex/waitwake.c:184
 do_futex+0x35d/0x3e0 kernel/futex/syscalls.c:111
 __do_sys_futex kernel/futex/syscalls.c:183 [inline]
 __se_sys_futex+0x36f/0x3f0 kernel/futex/syscalls.c:164
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fa658b8ebe9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fa6599a20e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: ffffffffffffffda RBX: 00007fa658db5fa8 RCX: 00007fa658b8ebe9
RDX: 00000000000f4240 RSI: 0000000000000081 RDI: 00007fa658db5fac
RBP: 00007fa658db5fa0 R08: 0000000000745d1e R09: 0000000000000000
R10: ffffffffffffffff R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa658db6038 R14: 00007fff1c7f3bc0 R15: 00007fff1c7f3ca8
 </TASK>

Crashes (5):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/08/21 11:48 linux-6.6.y bb9c90ab9c5a 0b9605c8 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf INFO: rcu detected stall in futex
2025/08/22 15:23 linux-6.6.y bb9c90ab9c5a bf27483f .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf INFO: rcu detected stall in futex
2025/08/15 16:30 linux-6.6.y bb9c90ab9c5a 1804e95e .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf INFO: rcu detected stall in futex
2025/08/14 14:48 linux-6.6.y 3a8ababb8b6a 5d8c2ac2 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf INFO: rcu detected stall in futex
2025/08/10 09:29 linux-6.6.y 3a8ababb8b6a 32a0e5ed .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf INFO: rcu detected stall in futex
* Struck through repros no longer work on HEAD.