syzbot

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
	(detected by 1, t=10502 jiffies, g=6245, q=124)
rcu: All QSes seen, last rcu_preempt kthread activity 10503 (4294953888-4294943385), jiffies_till_next_fqs=1, root ->qsmask 0x0
blkid           R  running task    28264  8220   8169 0x0000400a
Call Trace:
 <IRQ>
 sched_show_task+0x40f/0x560 kernel/sched/core.c:5954
 print_other_cpu_stall kernel/rcu/tree_stall.h:410 [inline]
 check_cpu_stall kernel/rcu/tree_stall.h:538 [inline]
 rcu_pending kernel/rcu/tree.c:2827 [inline]
 rcu_sched_clock_irq+0x1861/0x1ad0 kernel/rcu/tree.c:2271
 update_process_times+0x12d/0x180 kernel/time/timer.c:1726
 tick_sched_handle kernel/time/tick-sched.c:167 [inline]
 tick_sched_timer+0x263/0x420 kernel/time/tick-sched.c:1310
 __run_hrtimer kernel/time/hrtimer.c:1517 [inline]
 __hrtimer_run_queues+0x403/0x840 kernel/time/hrtimer.c:1579
 hrtimer_interrupt+0x38c/0xda0 kernel/time/hrtimer.c:1641
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1110 [inline]
 smp_apic_timer_interrupt+0x109/0x280 arch/x86/kernel/apic/apic.c:1135
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:829
 </IRQ>
RIP: 0010:free_thread_stack+0x15b/0x590 kernel/fork.c:280
Code: 2e 00 74 08 4c 89 e7 e8 43 a0 69 00 49 8b 1c 24 48 83 c3 08 48 89 d8 48 c1 e8 03 42 80 3c 28 00 74 08 48 89 df e8 25 a0 69 00 <48> 8b 3b be fc ff ff ff e8 28 04 00 00 43 80 3c 2e 00 74 08 4c 89
RSP: 0018:ffffc90002207538 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
RAX: 1ffff1100d851c71 RBX: ffff88806c28e388 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffea0001b0ac00
RBP: ffffc90002207570 R08: 000000000003a728 R09: ffffed101509bea7
R10: ffffed101509bea7 R11: 0000000000000000 R12: ffff88806c28e420
R13: dffffc0000000000 R14: 1ffff1100d851c84 R15: ffff8880a84df528
 release_task_stack kernel/fork.c:440 [inline]
 put_task_stack+0xa3/0x130 kernel/fork.c:451
 finish_task_switch+0x3f1/0x550 kernel/sched/core.c:3256
 context_switch kernel/sched/core.c:3388 [inline]
 __schedule+0x9a8/0xcc0 kernel/sched/core.c:4081
 preempt_schedule_irq+0xc1/0x140 kernel/sched/core.c:4338
 retint_kernel+0x1b/0x2b
RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:752 [inline]
RIP: 0010:slab_alloc mm/slab.c:3313 [inline]
RIP: 0010:__do_kmalloc mm/slab.c:3654 [inline]
RIP: 0010:__kmalloc+0x1d3/0x340 mm/slab.c:3665
Code: 00 48 89 df 57 9d 0f 1f 44 00 00 e8 c7 9e ca ff eb 1d e8 60 9c ca ff 48 83 3d 90 fe 58 07 00 0f 84 66 01 00 00 48 89 df 57 9d <0f> 1f 44 00 00 48 8b 7d d0 41 0f 18 0f e9 26 00 00 00 44 89 f0 c1
RSP: 0018:ffffc90002207780 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff13
RAX: ffff88809179ae14 RBX: 0000000000000286 RCX: ffff88809179a580
RDX: 0000000000000000 RSI: ffffffff8356314c RDI: 0000000000000286
RBP: ffffc900022077c0 R08: ffff88809179add8 R09: ffffed1015500341
R10: ffffed1015500341 R11: 0000000000000000 R12: 0000000000001000
R13: ffff8880aa802000 R14: 0000000000000c40 R15: ffff88806c26c000
 kmalloc include/linux/slab.h:561 [inline]
 tomoyo_realpath_from_path+0xdc/0x7c0 security/tomoyo/realpath.c:277
 tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
 tomoyo_check_open_permission+0x1ce/0x9d0 security/tomoyo/file.c:771
 tomoyo_file_open+0x141/0x190 security/tomoyo/tomoyo.c:319
 security_file_open+0x65/0x2f0 security/security.c:1497
 do_dentry_open+0x351/0x10c0 fs/open.c:784
 vfs_open+0x73/0x80 fs/open.c:914
 do_last fs/namei.c:3412 [inline]
 path_openat+0x1397/0x44a0 fs/namei.c:3529
 do_filp_open+0x192/0x3d0 fs/namei.c:3559
 do_sys_open+0x29f/0x560 fs/open.c:1097
 __do_sys_open fs/open.c:1115 [inline]
 __se_sys_open fs/open.c:1110 [inline]
 __x64_sys_open+0x87/0x90 fs/open.c:1110
 do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x7f24a4618120
Code: 48 8b 15 1b 4d 2b 00 f7 d8 64 89 02 83 c8 ff c3 90 90 90 90 90 90 90 90 90 90 83 3d d5 a4 2b 00 00 75 10 b8 02 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 31 c3 48 83 ec 08 e8 5e 8c 01 00 48 89 04 24
RSP: 002b:00007fff600d0948 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f24a4618120
RDX: 00007fff600d2f35 RSI: 0000000000000000 RDI: 00007fff600d2f35
RBP: 0000000000000000 R08: 0000000000000078 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000fed030
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000005
rcu: rcu_preempt kthread starved for 10544 jiffies! g6245 f0x2 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0
rcu: RCU grace-period kthread stack dump:
rcu_preempt     R  running task    29032    10      2 0x80004000
Call Trace:
 context_switch kernel/sched/core.c:3385 [inline]
 __schedule+0x9a0/0xcc0 kernel/sched/core.c:4081
 schedule+0x181/0x210 kernel/sched/core.c:4155
 schedule_timeout+0x14f/0x240 kernel/time/timer.c:1895
 rcu_gp_fqs_loop kernel/rcu/tree.c:1661 [inline]
 rcu_gp_kthread+0xed8/0x1770 kernel/rcu/tree.c:1821
 kthread+0x332/0x350 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352