syzbot

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	1-...!: (1 GPs behind) idle=572/1/0x4000000000000002 softirq=97995/97996 fqs=5 
rcu: 	 (t=10501 jiffies g=141781 q=129)
rcu: rcu_preempt kthread starved for 10491 jiffies! g141781 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0
rcu: RCU grace-period kthread stack dump:
rcu_preempt     R  running task    29168    10      2 0x80000000
Call Trace:
 context_switch kernel/sched/core.c:2877 [inline]
 __schedule+0x813/0x1cc0 kernel/sched/core.c:3518
 schedule+0x92/0x180 kernel/sched/core.c:3562
 schedule_timeout+0x4db/0xfd0 kernel/time/timer.c:1803
 rcu_gp_fqs_loop kernel/rcu/tree.c:1971 [inline]
 rcu_gp_kthread+0x962/0x17b0 kernel/rcu/tree.c:2128
 kthread+0x357/0x430 kernel/kthread.c:253
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352
NMI backtrace for cpu 1
CPU: 1 PID: 29295 Comm: syz-executor.5 Not tainted 5.1.0-rc7+ #92
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x172/0x1f0 lib/dump_stack.c:113
 nmi_cpu_backtrace.cold+0x63/0xa4 lib/nmi_backtrace.c:101
 nmi_trigger_cpumask_backtrace+0x1be/0x236 lib/nmi_backtrace.c:62
 arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
 trigger_single_cpu_backtrace include/linux/nmi.h:164 [inline]
 rcu_dump_cpu_stacks+0x183/0x1cf kernel/rcu/tree.c:1223
 print_cpu_stall kernel/rcu/tree.c:1360 [inline]
 check_cpu_stall kernel/rcu/tree.c:1434 [inline]
 rcu_pending kernel/rcu/tree.c:3103 [inline]
 rcu_sched_clock_irq.cold+0x500/0xa4a kernel/rcu/tree.c:2544
 update_process_times+0x32/0x80 kernel/time/timer.c:1635
 tick_sched_handle+0xa2/0x190 kernel/time/tick-sched.c:161
 tick_sched_timer+0x47/0x130 kernel/time/tick-sched.c:1271
 __run_hrtimer kernel/time/hrtimer.c:1389 [inline]
 __hrtimer_run_queues+0x33e/0xde0 kernel/time/hrtimer.c:1451
 hrtimer_interrupt+0x314/0x770 kernel/time/hrtimer.c:1509
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1035 [inline]
 smp_apic_timer_interrupt+0x120/0x570 arch/x86/kernel/apic/apic.c:1060
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:807
 </IRQ>
RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:767 [inline]
RIP: 0010:slab_alloc mm/slab.c:3386 [inline]
RIP: 0010:kmem_cache_alloc+0x28b/0x6f0 mm/slab.c:3555
Code: 7e 0f 85 cd fe ff ff e8 54 2a 58 ff e9 c3 fe ff ff e8 39 bd cd ff 48 83 3d f1 5a ea 06 00 0f 84 15 03 00 00 48 8b 7d d0 57 9d <0f> 1f 44 00 00 e9 60 fe ff ff 31 d2 be a2 01 00 00 48 c7 c7 0a fe
RSP: 0018:ffff888065307d30 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff13
RAX: 0000000000000007 RBX: 0000000000000cc0 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000006 RDI: 0000000000000286
RBP: ffff888065307d98 R08: ffff8880a0324500 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff88821bc45b00
R13: ffff88821bc45b00 R14: 0000000000000cc0 R15: ffff888081b221c0
 getname_flags fs/namei.c:138 [inline]
 getname_flags+0xd6/0x5b0 fs/namei.c:128
 user_path_at_empty+0x2f/0x50 fs/namei.c:2606
 user_path_at include/linux/namei.h:60 [inline]
 path_setxattr+0xae/0x1b0 fs/xattr.c:464
 __do_sys_setxattr fs/xattr.c:484 [inline]
 __se_sys_setxattr fs/xattr.c:480 [inline]
 __x64_sys_setxattr+0xc4/0x150 fs/xattr.c:480
 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x2000068b
Code: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 98 a8 4a 2a e9 2c 21 1c 42 0f 05 <bf> 03 00 00 00 c4 a3 7b f0 c5 5c 41 e2 e9 2e 36 3e 46 0f 1a 70 00
RSP: 002b:00007f9275772bd8 EFLAGS: 00000282 ORIG_RAX: 00000000000000bc
RAX: ffffffffffffffda RBX: 0000000000000009 RCX: 000000002000068b
RDX: e27eb1bea58e8070 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 0000000000000078 R08: 0000000000000005 R09: 0000000000000006
R10: 0000000000000007 R11: 0000000000000282 R12: 000000000000000b
R13: 000000000000000c R14: 000000000000000d R15: 00000000ffffffff