INFO: rcu detected stall in sys_rt

Kernel	Title	Rank 🛈	Repro	Cause bisect	Fix bisect	Count	Last	Reported	Patched	Status
linux-5.15	INFO: rcu detected stall in sys_rt_sigreturn missing-backport origin:lts-only	1	C		done	87	12d	519d	0/3	upstream: reported C repro on 2024/04/01 14:20
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P5156/1:b..l
rcu: 	(detected by 1, t=10503 jiffies, g=12701, q=649 ncpus=2)
task:udevd           state:R  running task     stack:25160 pid:5156  ppid:1      flags:0x00004002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5381 [inline]
 __schedule+0x14d2/0x44d0 kernel/sched/core.c:6700
 preempt_schedule_common+0x82/0xc0 kernel/sched/core.c:6867
 preempt_schedule+0xab/0xc0 kernel/sched/core.c:6891
 preempt_schedule_thunk+0x1a/0x30 arch/x86/entry/thunk_64.S:45
 __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]
 _raw_spin_unlock_irqrestore+0xfa/0x110 kernel/locking/spinlock.c:194
 spin_unlock_irqrestore include/linux/spinlock.h:406 [inline]
 __wake_up_common_lock kernel/sched/wait.c:140 [inline]
 __wake_up_sync_key+0x11f/0x190 kernel/sched/wait.c:213
 sock_def_readable+0x1e1/0x430 net/core/sock.c:3329
 __netlink_sendskb net/netlink/af_netlink.c:1276 [inline]
 netlink_sendskb+0x9b/0x130 net/netlink/af_netlink.c:1282
 netlink_sendmsg+0x8c1/0xbe0 net/netlink/af_netlink.c:1904
 sock_sendmsg_nosec net/socket.c:730 [inline]
 __sock_sendmsg net/socket.c:745 [inline]
 ____sys_sendmsg+0x5bf/0x950 net/socket.c:2595
 ___sys_sendmsg+0x220/0x290 net/socket.c:2649
 __sys_sendmsg net/socket.c:2678 [inline]
 __do_sys_sendmsg net/socket.c:2687 [inline]
 __se_sys_sendmsg+0x1a5/0x270 net/socket.c:2685
 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: 0033:0x7f1b49ea7407
RSP: 002b:00007ffe69de6a20 EFLAGS: 00000202 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f1b4a5cb880 RCX: 00007f1b49ea7407
RDX: 0000000000000000 RSI: 00007ffe69de6a80 RDI: 0000000000000004
RBP: 00005641b9e71060 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00000000000000b3
R13: 00005641b9e4f9e0 R14: 0000000000000000 R15: 0000000000000000
 </TASK>
rcu: rcu_preempt kthread starved for 10498 jiffies! g12701 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->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:R  running task     stack:27528 pid:17    ppid:2      flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5381 [inline]
 __schedule+0x14d2/0x44d0 kernel/sched/core.c:6700
 schedule+0xbd/0x170 kernel/sched/core.c:6774
 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:
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 6152 Comm: syz.0.82 Not tainted 6.6.101-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
RIP: 0010:__rq_lockp kernel/sched/sched.h:1245 [inline]
RIP: 0010:raw_spin_rq_lock_nested+0xc7/0x140 kernel/sched/core.c:567
Code: 81 00 4c 8b 6d 00 4c 89 ef 89 de e8 13 5a 1b 09 48 b8 00 00 00 00 00 fc ff df 41 0f b6 04 07 84 c0 75 5b 48 8b 04 24 83 38 00 <4c> 89 f0 74 1d 48 b8 00 00 00 00 00 fc ff df 41 80 3c 04 00 74 08
RSP: 0018:ffffc90000007c40 EFLAGS: 00000002
RAX: ffff8880b8e3d198 RBX: 0000000000000000 RCX: dffffc0000000000
RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffffc90000007bc0
RBP: ffff8880b8e3d188 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff52000000f78 R12: 1ffff110171c7a31
R13: ffff8880b8e3c440 R14: ffff8880b8e3c440 R15: 1ffff110171c7a33
FS:  00007f40f9a666c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f40f8db6098 CR3: 000000007e0af000 CR4: 00000000003506f0
Call Trace:
 <IRQ>
 raw_spin_rq_lock kernel/sched/sched.h:1372 [inline]
 _raw_spin_rq_lock_irqsave kernel/sched/sched.h:1391 [inline]
 rq_lock_irqsave kernel/sched/sched.h:1665 [inline]
 update_blocked_averages+0x101/0x1560 kernel/sched/fair.c:9453
 run_rebalance_domains+0xf9/0x1c0 kernel/sched/fair.c:12457
 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:__raw_spin_unlock_irq include/linux/spinlock_api_smp.h:160 [inline]
RIP: 0010:_raw_spin_unlock_irq+0x29/0x50 kernel/locking/spinlock.c:202
Code: 00 f3 0f 1e fa 53 48 89 fb 48 83 c7 18 48 8b 74 24 08 e8 9a c8 f0 f6 48 89 df e8 b2 9a f1 f6 e8 4d 37 15 f7 fb bf 01 00 00 00 <e8> 92 b2 e4 f6 65 8b 05 93 f8 8c 75 85 c0 74 02 5b c3 e8 70 da 89
RSP: 0018:ffffc90004e87cf0 EFLAGS: 00000286
RAX: 4b71475245d9b300 RBX: ffff8880240840c0 RCX: 4b71475245d9b300
RDX: dffffc0000000000 RSI: ffffffff8aaaba40 RDI: 0000000000000001
RBP: ffffc90004e87f10 R08: ffffffff8e4a84ef R09: 1ffffffff1c9509d
R10: dffffc0000000000 R11: fffffbfff1c9509e R12: 00007f40f9a65b38
R13: 1ffff920009d0ffe R14: 00000000ffffffff R15: 1ffff920009d0fa8
 __ia32_sys_rt_sigreturn+0x1ec/0x7b0 arch/x86/kernel/signal_64.c:261
 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: 0033:0x7f40f8b2add9
Code: 64 c7 00 16 00 00 00 b8 ff ff ff ff c3 0f 1f 40 00 90 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 c7 c0 0f 00 00 00 0f 05 <0f> 1f 80 00 00 00 00 48 81 ec 48 01 00 00 49 89 d0 64 48 8b 04 25
RSP: 002b:00007f40f9a65b40 EFLAGS: 00000246 ORIG_RAX: 000000000000000f
RAX: ffffffffffffffda RBX: 00007f40f8db6098 RCX: 00007f40f8b2add9
RDX: 00007f40f9a65b40 RSI: 00007f40f9a65c70 RDI: 0000000000000011
RBP: 00007f40f8db6090 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f40f8db6128 R14: 00007ffe5b7355d0 R15: 00007ffe5b7356b8
 </TASK>