INFO: rcu detected stall in futex

Status: fixed on 2025/10/06 10:09
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+795c184c6744be404955@syzkaller.appspotmail.com
Fix commit: b41642c87716 rcu: Fix rcu_read_unlock() deadloop due to IRQ work
First crash: 358d, last: 341d
Fix bisection: fixed by (bisect log) :
commit e7a375453cca2b8a0d2fa1b82b913f3fed7c0507
Author: Joel Fernandes <joelagnelf@nvidia.com>
Date: Tue Jul 8 14:22:19 2025 +0000

  rcu: Fix rcu_read_unlock() deadloop due to IRQ work

  
▶ ▼ 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 (12)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.6 INFO: rcu detected stall in futex (2) origin:lts-only 1 syz, C inconclusive 70 7d08h 277d 0/2 upstream: reported C repro on 2025/10/31 01:02
upstream INFO: rcu detected stall in sys_futex (7) prio:high kernel 1 syz error error 138 4d10h 770d 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, C error 95 1d13h 789d 0/3 upstream: reported C repro on 2024/06/05 16:49
upstream INFO: rcu detected stall in futex kvm 1 1 2024d 2024d 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, C done 66 19h57m 1125d 0/3 upstream: reported C repro on 2023/07/05 11:35
upstream INFO: rcu detected stall in sys_futex (3) mm 1 959 2399d 2448d 0/29 auto-closed as invalid on 2020/03/08 12:44
upstream INFO: rcu detected stall in sys_futex (2) kernel 1 6 2567d 2711d 0/29 auto-closed as invalid on 2019/10/25 14:11
upstream INFO: rcu detected stall in sys_futex (4) kernel 1 1 1648d 1648d 0/29 closed as invalid on 2022/02/08 10:00
upstream INFO: rcu detected stall in sys_futex kernel 1 1 2773d 2773d 0/29 closed as invalid on 2018/12/31 04:10
linux-5.15 INFO: rcu detected stall in sys_futex 1 4 945d 1119d 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 1379d 1624d 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 948d 1183d 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=08bc/1/0x4000000000000000 softirq=66406/66407 fqs=62
rcu: 	(detected by 1, t=10505 jiffies, g=83117, q=1461 ncpus=2)
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 15800 Comm: syz.0.3763 Not tainted 6.6.102-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
RIP: 0010:check_preemption_disabled+0x3/0x110 lib/smp_processor_id.c:13
Code: ff ff ff cc cc cc cc f3 0f 1e fa 48 c7 c7 60 66 fc 8a 48 c7 c6 a0 66 fc 8a eb 0c 66 2e 0f 1f 84 00 00 00 00 00 66 90 55 41 57 <41> 56 53 48 83 ec 10 65 48 8b 04 25 28 00 00 00 48 89 44 24 08 65
RSP: 0018:ffffc90000007168 EFLAGS: 00000007
RAX: 0000000000000001 RBX: 0000000000000000 RCX: ffffffff8166ff4c
RDX: 0000000000000000 RSI: ffffffff8afc66a0 RDI: ffffffff8afc6660
RBP: ffffc900000072a8 R08: ffffffff8e4a882f R09: 1ffffffff1c95105
R10: dffffc0000000000 R11: fffffbfff1c95106 R12: 1ffff92000000e40
R13: ffffffff8cd2fbe0 R14: 0000000000000000 R15: dffffc0000000000
FS:  00007ff7a35db6c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555584582588 CR3: 0000000049185000 CR4: 00000000003506f0
DR0: 0000200000000300 DR1: 0000000000000000 DR2: 0000200000000300
DR3: 0000200000000300 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
 <IRQ>
 rcu_dynticks_curr_cpu_in_eqs include/linux/context_tracking.h:122 [inline]
 rcu_is_watching+0x15/0xb0 kernel/rcu/tree.c:700
 trace_lock_acquire include/trace/events/lock.h:24 [inline]
 lock_acquire+0xcb/0x410 kernel/locking/lockdep.c:5725
 rcu_lock_acquire include/linux/rcupdate.h:334 [inline]
 rcu_read_lock include/linux/rcupdate.h:786 [inline]
 __perf_output_begin kernel/events/ring_buffer.c:163 [inline]
 perf_output_begin_forward+0xc0/0xa20 kernel/events/ring_buffer.c:273
 __perf_event_output kernel/events/core.c:7974 [inline]
 perf_event_output_forward+0x22b/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:ffffc90000007b00 EFLAGS: 00000206
RAX: 1de17cbbc4fbef00 RBX: 1ffff92000000f68 RCX: 1de17cbbc4fbef00
RDX: dffffc0000000000 RSI: ffffffff8aaab9c0 RDI: ffffffff8afc66c0
RBP: ffffc90000007bf0 R08: ffffffff90da35d7 R09: 1ffffffff21b46ba
R10: dffffc0000000000 R11: fffffbfff21b46bb 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]
 ieee80211_iterate_active_interfaces_atomic+0x15a/0x180 net/mac80211/util.c:804
 mac80211_hwsim_beacon+0xbb/0x1b0 drivers/net/wireless/virtual/mac80211_hwsim.c:2295
 __run_hrtimer kernel/time/hrtimer.c:1755 [inline]
 __hrtimer_run_queues+0x51e/0xc40 kernel/time/hrtimer.c:1819
 hrtimer_run_softirq+0x187/0x2b0 kernel/time/hrtimer.c:1836
 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:__sanitizer_cov_trace_pc+0x3b/0x60 kernel/kcov.c:219
Code: 8b 15 d1 2e 7e 7e 81 e2 00 01 ff 00 74 11 81 fa 00 01 00 00 75 35 83 b9 1c 16 00 00 00 74 2c 8b 91 f8 15 00 00 83 fa 02 75 21 <48> 8b 91 00 16 00 00 48 8b 32 48 8d 7e 01 8b 89 fc 15 00 00 48 39
RSP: 0018:ffffc9000d7a7b48 EFLAGS: 00000246
RAX: ffffffff8a5cd69f RBX: ffffc90000a29dc8 RCX: ffff888028d38000
RDX: 0000000000000002 RSI: 0000000000005431 RDI: 0000000000005432
RBP: 0000000000000001 R08: ffff88802761bc2b R09: 1ffff11004ec3785
R10: dffffc0000000000 R11: ffffed1004ec3786 R12: dffffc0000000000
R13: ffffc9000d867c80 R14: ffffc9000d867c50 R15: ffffc9000d867c68
 plist_check_head lib/plist.c:59 [inline]
 plist_del+0x4f/0x3f0 lib/plist.c:114
 __futex_unqueue+0xf0/0x160 kernel/futex/core.c:518
 futex_wake_mark+0xec/0x150 kernel/futex/waitwake.c:123
 futex_wake+0x315/0x4b0 kernel/futex/waitwake.c:177
 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: 0033:0x7ff7a278ebe9
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:00007ff7a35db0e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: ffffffffffffffda RBX: 00007ff7a29b5fa8 RCX: 00007ff7a278ebe9
RDX: 00000000000f4240 RSI: 0000000000000081 RDI: 00007ff7a29b5fac
RBP: 00007ff7a29b5fa0 R08: 0000000000745d1e R09: 0000000000000000
R10: 000000000000000e R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff7a29b6038 R14: 00007fff21539f40 R15: 00007fff2153a028
 </TASK>
rcu: rcu_preempt kthread starved for 10195 jiffies! g83117 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:26568 pid:17    ppid:2      flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5380 [inline]
 __schedule+0x14d2/0x44d0 kernel/sched/core.c:6699
 schedule+0xbd/0x170 kernel/sched/core.c:6773
 schedule_timeout+0x160/0x280 kernel/time/timer.c:2167
 rcu_gp_fqs_loop+0x302/0x1560 kernel/rcu/tree.c:1667
 rcu_gp_kthread+0x99/0x380 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: 1 PID: 15799 Comm: syz.0.3763 Not tainted 6.6.102-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
RIP: 0010:pv_native_safe_halt+0x13/0x20 arch/x86/kernel/paravirt.c:148
Code: cc cc cc cc cc cc cc f3 0f 1e fa 0f 0b 66 2e 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 66 90 0f 00 2d e3 e6 3a 00 f3 0f 1e fa fb f4 <c3> cc cc cc cc cc cc cc cc cc cc cc cc 66 0f 1f 00 55 41 57 41 56
RSP: 0018:ffffc9000d867878 EFLAGS: 000002d3
RAX: ffffffff813a13aa RBX: 0000000000000003 RCX: ffff88802761bc00
RDX: 0000000000000000 RSI: ffffffff8aaab9c0 RDI: ffffffff8afc66c0
RBP: ffffc9000d867950 R08: ffffffff90da35d7 R09: 1ffffffff21b46ba
R10: dffffc0000000000 R11: fffffbfff21b46bb R12: dffffc0000000000
R13: 0000000000000200 R14: 0000000000000003 R15: 1ffff92001b0cf14
FS:  0000555567f00500(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555567f1b5c8 CR3: 0000000049185000 CR4: 00000000003506e0
DR0: 0000200000000300 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
 <TASK>
 arch_safe_halt arch/x86/include/asm/paravirt.h:108 [inline]
 kvm_wait+0x22f/0x290 arch/x86/kernel/kvm.c:1058
 pv_wait arch/x86/include/asm/paravirt.h:598 [inline]
 pv_wait_head_or_lock kernel/locking/qspinlock_paravirt.h:470 [inline]
 __pv_queued_spin_lock_slowpath+0x61a/0x9d0 kernel/locking/qspinlock.c:511
 pv_queued_spin_lock_slowpath arch/x86/include/asm/paravirt.h:586 [inline]
 queued_spin_lock_slowpath arch/x86/include/asm/qspinlock.h:51 [inline]
 queued_spin_lock include/asm-generic/qspinlock.h:114 [inline]
 do_raw_spin_lock+0x24e/0x2c0 kernel/locking/spinlock_debug.c:115
 spin_lock include/linux/spinlock.h:351 [inline]
 futex_unqueue+0x4e/0xf0 kernel/futex/core.c:597
 futex_wait+0x1a7/0x530 kernel/futex/waitwake.c:660
 do_futex+0x2ff/0x3e0 kernel/futex/syscalls.c:106
 __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: 0033:0x7ff7a278ebe9
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:00007fff2153a188 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: ffffffffffffffda RBX: 0000000000090db9 RCX: 00007ff7a278ebe9
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007ff7a29b5fac
RBP: 0000000000000032 R08: 0000000000745d1e R09: 000000122153a47f
R10: 00007fff2153a280 R11: 0000000000000246 R12: 00007ff7a29b5fac
R13: 00007fff2153a280 R14: 0000000000090deb R15: 00007fff2153a2a0
 </TASK>

Crashes (6):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/08/27 22:24 linux-6.6.y bb9c90ab9c5a e12e5ba4 .config console log report info [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
2025/08/21 11:48 linux-6.6.y bb9c90ab9c5a 0b9605c8 .config console log report syz / log C 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.