syzbot

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P5245/1:b..l
	(detected by 1, t=10502 jiffies, g=13841, q=387)
task:rm              state:R  running task     stack:27200 pid: 5245 ppid:  5188 flags:0x00004002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5030 [inline]
 __schedule+0x11b8/0x43b0 kernel/sched/core.c:6376
 preempt_schedule_irq+0xb1/0x150 kernel/sched/core.c:6780
 irqentry_exit+0x63/0x70 kernel/entry/common.c:432
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:seqcount_lockdep_reader_access+0x17a/0x1c0 include/linux/seqlock.h:106
Code: ff 4d 85 ed 75 16 e8 e5 43 ac ff eb 15 e8 de 43 ac ff e8 79 73 d5 07 4d 85 ed 74 ea e8 cf 43 ac ff fb 48 c7 04 24 0e 36 e0 45 <4b> c7 04 27 00 00 00 00 66 43 c7 44 27 09 00 00 43 c6 44 27 0b 00
RSP: 0018:ffffc900031cf700 EFLAGS: 00000293
RAX: ffffffff81cb79a1 RBX: 0000000000000000 RCX: ffff888022265940
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc900031cf7b0 R08: dffffc0000000000 R09: fffffbfff1ad1706
R10: fffffbfff1ad1706 R11: 1ffffffff1ad1705 R12: dffffc0000000000
R13: 0000000000000200 R14: ffffffff81cb8812 R15: 1ffff92000639ee0
 __follow_mount_rcu fs/namei.c:1457 [inline]
 handle_mounts fs/namei.c:1490 [inline]
 step_into+0x642/0xd00 fs/namei.c:1806
 link_path_walk+0x662/0xd40 fs/namei.c:-1
 path_lookupat+0x9d/0x440 fs/namei.c:2454
 filename_lookup+0x1e2/0x4f0 fs/namei.c:2484
 user_path_at_empty+0x40/0x190 fs/namei.c:2883
 user_path_at include/linux/namei.h:57 [inline]
 user_statfs+0x9e/0x5b0 fs/statfs.c:103
 __do_sys_statfs fs/statfs.c:195 [inline]
 __se_sys_statfs fs/statfs.c:192 [inline]
 __x64_sys_statfs+0xdd/0x1a0 fs/statfs.c:192
 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: 0033:0x7f70c8cf968a
RSP: 002b:00007ffd0dcd60c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000089
RAX: ffffffffffffffda RBX: 00007f70c8c1e4f8 RCX: 00007f70c8cf968a
RDX: 00007f70c8c2019c RSI: 00007ffd0dcd6140 RDI: 00007f70c8c16723
RBP: 00007f70c8c16723 R08: 0000000000000000 R09: 000000000000000d
R10: 00007ffd0dcd5ef0 R11: 0000000000000246 R12: 00007ffd0dcd6140
R13: 00007ffd0dcd62b8 R14: 00007ffd0dcd62d8 R15: 0000000000000000
 </TASK>
rcu: rcu_preempt kthread starved for 9909 jiffies! g13841 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:27584 pid:   15 ppid:     2 flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5030 [inline]
 __schedule+0x11b8/0x43b0 kernel/sched/core.c:6376
 schedule+0x11b/0x1e0 kernel/sched/core.c:6459
 schedule_timeout+0x15c/0x280 kernel/time/timer.c:1914
 rcu_gp_fqs_loop+0x29e/0x11b0 kernel/rcu/tree.c:1972
 rcu_gp_kthread+0x98/0x350 kernel/rcu/tree.c:2145
 kthread+0x436/0x520 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:
NMI backtrace for cpu 1
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.15.180-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/19/2025
Call Trace:
 <IRQ>
 dump_stack_lvl+0x168/0x230 lib/dump_stack.c:106
 nmi_cpu_backtrace+0x397/0x3d0 lib/nmi_backtrace.c:111
 nmi_trigger_cpumask_backtrace+0x163/0x280 lib/nmi_backtrace.c:62
 trigger_single_cpu_backtrace include/linux/nmi.h:166 [inline]
 rcu_check_gp_kthread_starvation+0x1cd/0x250 kernel/rcu/tree_stall.h:487
 print_other_cpu_stall+0x10c8/0x1220 kernel/rcu/tree_stall.h:592
 check_cpu_stall kernel/rcu/tree_stall.h:745 [inline]
 rcu_pending kernel/rcu/tree.c:3932 [inline]
 rcu_sched_clock_irq+0x831/0x1110 kernel/rcu/tree.c:2619
 update_process_times+0x193/0x200 kernel/time/timer.c:1818
 tick_sched_handle kernel/time/tick-sched.c:254 [inline]
 tick_sched_timer+0x37d/0x560 kernel/time/tick-sched.c:1473
 __run_hrtimer kernel/time/hrtimer.c:1690 [inline]
 __hrtimer_run_queues+0x4fe/0xc40 kernel/time/hrtimer.c:1754
 hrtimer_interrupt+0x3bb/0x8d0 kernel/time/hrtimer.c:1816
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1097 [inline]
 __sysvec_apic_timer_interrupt+0x137/0x4a0 arch/x86/kernel/apic/apic.c:1114
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
 sysvec_apic_timer_interrupt+0x9b/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:default_idle+0xb/0x10 arch/x86/kernel/process.c:723
Code: bf 48 89 df e8 b6 fc 12 f8 eb b5 e8 4f be f6 ff 00 00 cc cc 00 00 cc cc 00 00 cc cc 00 00 cc 66 90 0f 00 2d 17 96 5b 00 fb f4 <c3> 0f 1f 40 00 41 57 41 56 53 49 be 00 00 00 00 00 fc ff df 65 48
RSP: 0018:ffffc90000d67d48 EFLAGS: 000002c2
RAX: fc485f34f0add500 RBX: ffff88813fe28000 RCX: fc485f34f0add500
RDX: 0000000000000001 RSI: ffffffff8a0b12c0 RDI: ffffffff8a59a340
RBP: ffffc90000d67e80 R08: dffffc0000000000 R09: ffffed101722765a
R10: ffffed101722765a R11: 1ffff11017227659 R12: ffffffff8d68b828
R13: 0000000000000001 R14: 0000000000000001 R15: 1ffff11027fc5000
 default_idle_call+0x81/0xc0 kernel/sched/idle.c:112
 cpuidle_idle_call kernel/sched/idle.c:194 [inline]
 do_idle+0x21b/0x5b0 kernel/sched/idle.c:306
 cpu_startup_entry+0x14/0x20 kernel/sched/idle.c:403
 start_secondary+0x31f/0x430 arch/x86/kernel/smpboot.c:281
 secondary_startup_64_no_verify+0xb1/0xbb
 </TASK>