syzbot

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	1-...!: (1 GPs behind) idle=fa54/1/0x4000000000000000 softirq=58508/58509 fqs=569
	(t=10502 jiffies g=82065 q=203 ncpus=2)
rcu: rcu_preempt kthread starved for 9364 jiffies! g82065 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:27200 pid:16    ppid:2      flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5244 [inline]
 __schedule+0x10ec/0x40b0 kernel/sched/core.c:6561
 schedule+0xb9/0x180 kernel/sched/core.c:6637
 schedule_timeout+0x15c/0x280 kernel/time/timer.c:1965
 rcu_gp_fqs_loop+0x2f2/0x1310 kernel/rcu/tree.c:1706
 rcu_gp_kthread+0x95/0x380 kernel/rcu/tree.c:1905
 kthread+0x29d/0x330 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at native_safe_halt arch/x86/include/asm/irqflags.h:51 [inline]
NMI backtrace for cpu 0 skipped: idling at arch_safe_halt arch/x86/include/asm/irqflags.h:89 [inline]
NMI backtrace for cpu 0 skipped: idling at default_idle+0xb/0x10 arch/x86/kernel/process.c:741
CPU: 1 PID: 13538 Comm: syz.5.1649 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
RIP: 0010:_static_cpu_has arch/x86/include/asm/cpufeature.h:180 [inline]
RIP: 0010:pkru_write_default arch/x86/include/asm/pkru.h:56 [inline]
RIP: 0010:restore_fpregs_from_init_fpstate arch/x86/kernel/fpu/core.c:672 [inline]
RIP: 0010:fpu__clear_user_states+0x13f/0x260 arch/x86/kernel/fpu/core.c:727
Code: 51 00 be ff 00 06 00 48 c7 c7 40 34 5e 8c ba 01 00 00 00 e8 43 6b 00 00 48 c7 c7 80 34 5e 8c b8 ff 00 06 00 31 d2 48 0f ae 2f <e9> f7 00 00 00 e8 37 b6 51 00 48 c7 c0 a0 40 9b 8c 48 c1 e8 03 42
RSP: 0018:ffffc90004befc88 EFLAGS: 00000246
RAX: 00000000000600ff RBX: ffff88807c0c8000 RCX: 0000000000080000
RDX: 0000000000000000 RSI: 000000000007ffff RDI: ffffffff8c5e3480
RBP: 0000000000000000 R08: dffffc0000000000 R09: fffffbfff1c3ecb6
R10: fffffbfff1c3ecb6 R11: 1ffffffff1c3ecb5 R12: ffff88807c0c9900
R13: dffffc0000000000 R14: ffff88807c0c9900 R15: ffffffff812f17a6
FS:  00007f1aea8fb6c0(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffe7e814028 CR3: 0000000066cf7000 CR4: 00000000003526e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 handle_signal arch/x86/kernel/signal.c:844 [inline]
 arch_do_signal_or_restart+0xe9e/0x1230 arch/x86/kernel/signal.c:873
 exit_to_user_mode_loop+0x70/0x110 kernel/entry/common.c:174
 exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:210
 __syscall_exit_to_user_mode_work kernel/entry/common.c:292 [inline]
 syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:303
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:87
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f1ae99b7600
Code: 83 c0 16 83 e0 f7 74 12 50 48 8d 3d ca 3c 08 00 e8 d5 8e f8 ff 0f 1f 44 00 00 c3 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 <83> ff 21 74 0b c3 66 2e 0f 1f 84 00 00 00 00 00 55 53 48 89 f3 48
RSP: 002b:00007f1aea8fab38 EFLAGS: 00000246
RAX: 0000000000000000 RBX: 00007f1ae9be5fa8 RCX: 00007f1ae998eec9
RDX: 00007f1aea8fab40 RSI: 00007f1aea8fac70 RDI: 0000000000000021
RBP: 00007f1ae9be5fa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f1ae9be6038 R14: 00007fff0bbe0f70 R15: 00007fff0bbe1058
 </TASK>