INFO: rcu detected stall in alloc_fd

Status: upstream: reported on 2026/10/22 07:58
Reported-by: syzbot+c8b92d25b36ecf508666@syzkaller.appspotmail.com
First crash: 23h04m, last: 23h04m
▶ ▼ Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.1 INFO: rcu detected stall in alloc_fd (2) 1 syz, C 1 13d 13d 0/3 upstream: reported C repro on 2026/10/09 07:18
linux-6.1 INFO: rcu detected stall in alloc_fd 1 1 233d 233d 0/3 auto-obsoleted due to no activity on 2026/06/12 01:51

Sample crash report:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P25262/1:b..l
	(detected by 1, t=10506 jiffies, g=211317, q=282)
task:syz.6.16093     state:R  running task     stack:24400 pid:25262 ppid: 18211 flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5049 [inline]
 __schedule+0x11c3/0x4350 kernel/sched/core.c:6395
 preempt_schedule_common+0x82/0xd0 kernel/sched/core.c:6571
 preempt_schedule+0xbc/0xd0 kernel/sched/core.c:6596
 preempt_schedule_thunk+0x16/0x18 arch/x86/entry/thunk_64.S:34
 __local_bh_enable_ip+0x147/0x1c0 kernel/softirq.c:408
 rcu_read_unlock_bh include/linux/rcupdate.h:810 [inline]
 __dev_queue_xmit+0x1b64/0x2e50 net/core/dev.c:4342
 __bpf_tx_skb net/core/filter.c:2136 [inline]
 __bpf_redirect_no_mac net/core/filter.c:2170 [inline]
 __bpf_redirect+0x693/0xe90 net/core/filter.c:2193
 ____bpf_clone_redirect net/core/filter.c:2471 [inline]
 bpf_clone_redirect+0x2e1/0x460 net/core/filter.c:2434
 bpf_prog_1eda3e3d4f38ab1d+0x56/0x280
 bpf_dispatcher_nop_func include/linux/bpf.h:890 [inline]
 __bpf_prog_run include/linux/filter.h:628 [inline]
 bpf_prog_run include/linux/filter.h:635 [inline]
 bpf_test_run+0x2a8/0x800 net/bpf/test_run.c:119
 bpf_prog_test_run_skb+0x9fb/0x1190 net/bpf/test_run.c:678
 bpf_prog_test_run+0x31c/0x390 kernel/bpf/syscall.c:3374
 __sys_bpf+0x5a5/0x6f0 kernel/bpf/syscall.c:4675
 __do_sys_bpf kernel/bpf/syscall.c:4761 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:4759 [inline]
 __x64_sys_bpf+0x78/0x90 kernel/bpf/syscall.c:4759
 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: 0033:0x7ff1c96f0559
RSP: 002b:00007ff1c7926028 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00007ff1c9977090 RCX: 00007ff1c96f0559
RDX: 000000000000002c RSI: 0000200000002280 RDI: 000000000000000a
RBP: 00007ff1c9787b20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff1c9977128 R14: 00007ff1c9977090 R15: 00007ffc103da9e8
 </TASK>
rcu: rcu_preempt kthread timer wakeup didn't happen for 10499 jiffies! g211317 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402
rcu: 	Possible timer handling issue on cpu=0 timer-softirq=127708
rcu: rcu_preempt kthread starved for 10500 jiffies! g211317 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:27408 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 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 25260 Comm: syz.6.16093 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/07/2026
RIP: 0010:arch_atomic_read arch/x86/include/asm/atomic.h:29 [inline]
RIP: 0010:rcu_dynticks_curr_cpu_in_eqs kernel/rcu/tree.c:331 [inline]
RIP: 0010:rcu_is_watching+0x56/0xa0 kernel/rcu/tree.c:1123
Code: f0 48 c1 e8 03 42 80 3c 38 00 74 08 4c 89 f7 e8 60 a4 59 00 48 c7 c3 08 b3 03 00 49 03 1e 48 89 d8 48 c1 e8 03 42 0f b6 04 38 <84> c0 75 2b 8b 03 65 ff 0d a5 ab 9d 7e 74 08 24 01 5b 41 5e 41 5f
RSP: 0018:ffffc90000007300 EFLAGS: 00000802
RAX: 0000000000000000 RBX: ffff8880b8e3b308 RCX: 1de3663b74b39300
RDX: 0000000000000100 RSI: ffffffff8a7a4b20 RDI: ffffffff8a7a4ae0
RBP: ffffc90000007450 R08: dffffc0000000000 R09: 1ffffffff2202a18
R10: dffffc0000000000 R11: fffffbfff2202a19 R12: 1ffff92000000e74
R13: ffffc900000074a0 R14: ffffffff8be44820 R15: dffffc0000000000
FS:  00007ff1c79476c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 0000000033b07000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
 <IRQ>
 rcu_read_lock include/linux/rcupdate.h:741 [inline]
 __perf_output_begin kernel/events/ring_buffer.c:163 [inline]
 perf_output_begin_forward+0xc0/0xa30 kernel/events/ring_buffer.c:271
 __perf_event_output kernel/events/core.c:7814 [inline]
 perf_event_output_forward+0x19b/0x2e0 kernel/events/core.c:7832
 __perf_event_overflow+0x35f/0x550 kernel/events/core.c:9525
 perf_swevent_overflow kernel/events/core.c:9601 [inline]
 perf_swevent_event+0x4b8/0x540 kernel/events/core.c:9639
 perf_tp_event+0x324/0xbe0 kernel/events/core.c:10057
 perf_trace_run_bpf_submit+0xf3/0x1c0 kernel/events/core.c:10031
 perf_trace_preemptirq_template+0x2aa/0x360 include/trace/events/preemptirq.h:14
 trace_irq_enable_rcuidle+0x108/0x180 include/trace/events/preemptirq.h:40
 trace_hardirqs_on+0x57/0x80 kernel/trace/trace_preemptirq.c:44
 asm_sysvec_irq_work+0x16/0x20 arch/x86/include/asm/idtentry.h:713
RIP: 0010:rcu_read_unlock_special+0x7f/0x4a0 kernel/rcu/tree_plugin.h:674
Code: eb 03 48 b8 f1 f1 f1 f1 f8 f2 f2 f2 4a 89 04 2b 42 c7 44 2b 08 f8 f3 f3 f3 65 44 8b 35 82 fc 9c 7e 41 f7 c6 00 00 f0 00 74 40 <48> c7 44 24 20 0e 36 e0 45 4a c7 04 2b 00 00 00 00 42 c7 44 2b 08
RSP: 0018:ffffc90000007b00 EFLAGS: 00000206
RAX: 1de3663b74b39300 RBX: 1ffff92000000f64 RCX: 1de3663b74b39300
RDX: dffffc0000000000 RSI: ffffffff8a2b2b60 RDI: ffffffff8a7a4b40
RBP: ffffc90000007bd8 R08: ffffffff910150df R09: 1ffffffff2202a1b
R10: dffffc0000000000 R11: fffffbfff2202a1c R12: ffffffff8d123400
R13: dffffc0000000000 R14: 0000000000000246 R15: 0000000000000001
 __rcu_read_unlock+0x78/0xd0 kernel/rcu/tree_plugin.h:422
 rcu_read_unlock include/linux/rcupdate.h:772 [inline]
 ieee80211_iterate_active_interfaces_atomic+0x132/0x140 net/mac80211/util.c:831
 mac80211_hwsim_beacon+0x9b/0x180 drivers/net/wireless/mac80211_hwsim.c:1865
 __run_hrtimer kernel/time/hrtimer.c:1685 [inline]
 __hrtimer_run_queues+0x4ea/0xb60 kernel/time/hrtimer.c:1749
 hrtimer_run_softirq+0x176/0x240 kernel/time/hrtimer.c:1766
 handle_softirqs+0x336/0x830 kernel/softirq.c:576
 __do_softirq kernel/softirq.c:610 [inline]
 invoke_softirq kernel/softirq.c:450 [inline]
 __irq_exit_rcu+0x13b/0x230 kernel/softirq.c:659
 irq_exit_rcu+0x5/0x20 kernel/softirq.c:671
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
 sysvec_apic_timer_interrupt+0xa0/0xc0 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:find_next_fd fs/file.c:468 [inline]
RIP: 0010:alloc_fd+0x1a5/0x650 fs/file.c:494
Code: 89 df e8 3e f0 ed ff 44 89 e1 c1 e9 06 44 89 fa c1 ea 06 48 8b 3b 31 f6 49 c7 c0 ff ff ff ff 45 31 c9 e8 8e c4 17 02 48 89 c3 <c1> e3 06 89 df 44 89 fe e8 6e ac a8 ff 44 39 fb 73 55 e8 04 ab a8
RSP: 0018:ffffc9000320fe10 EFLAGS: 00000286
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000080000
RDX: ffffc900170f4000 RSI: 0000000000009ebf RDI: 0000000000009ec0
RBP: ffff88801f9670c0 R08: ffffffffffffffff R09: 0000000000000000
R10: dffffc0000000000 R11: fffff52000641fb0 R12: 0000000000000006
R13: ffff88801f967118 R14: ffff888036334680 R15: 0000000000000100
 __sys_socketpair+0x64/0x540 net/socket.c:1629
 __do_sys_socketpair net/socket.c:1705 [inline]
 __se_sys_socketpair net/socket.c:1702 [inline]
 __x64_sys_socketpair+0x97/0xb0 net/socket.c:1702
 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: 0033:0x7ff1c96f0559
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:00007ff1c7947028 EFLAGS: 00000246 ORIG_RAX: 0000000000000035
RAX: ffffffffffffffda RBX: 00007ff1c9976fa0 RCX: 00007ff1c96f0559
RDX: 0000000000000000 RSI: 0000000000000005 RDI: 0000000000000001
RBP: 00007ff1c9787b20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000200000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff1c9977038 R14: 00007ff1c9976fa0 R15: 00007ffc103da9e8
 </TASK>

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/10/22 07:58 linux-5.15.y 792fbe1537d8 4ba27f85 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: rcu detected stall in alloc_fd
* Struck through repros no longer work on HEAD.