syzbot

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	1-....: (10499 ticks this GP) idle=3b2/1/0x4000000000000000 softirq=147521/147521 fqs=5205 
	(t=10502 jiffies g=235761 q=1036)
NMI backtrace for cpu 1
CPU: 1 PID: 4659 Comm: syz-executor.0 Not tainted 5.8.0-rc6-syzkaller #0
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+0x1f0/0x31e lib/dump_stack.c:118
 nmi_cpu_backtrace+0x9f/0x180 lib/nmi_backtrace.c:101
 nmi_trigger_cpumask_backtrace+0x16a/0x280 lib/nmi_backtrace.c:62
 trigger_single_cpu_backtrace include/linux/nmi.h:164 [inline]
 rcu_dump_cpu_stacks+0x199/0x2a0 kernel/rcu/tree_stall.h:320
 print_cpu_stall kernel/rcu/tree_stall.h:553 [inline]
 check_cpu_stall kernel/rcu/tree_stall.h:627 [inline]
 rcu_pending kernel/rcu/tree.c:3489 [inline]
 rcu_sched_clock_irq+0x1928/0x1eb0 kernel/rcu/tree.c:2504
 update_process_times+0x12c/0x180 kernel/time/timer.c:1737
 tick_sched_handle kernel/time/tick-sched.c:176 [inline]
 tick_sched_timer+0x254/0x410 kernel/time/tick-sched.c:1320
 __run_hrtimer kernel/time/hrtimer.c:1520 [inline]
 __hrtimer_run_queues+0x42d/0x930 kernel/time/hrtimer.c:1584
 hrtimer_interrupt+0x373/0xd60 kernel/time/hrtimer.c:1646
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1080 [inline]
 __sysvec_apic_timer_interrupt+0xf0/0x260 arch/x86/kernel/apic/apic.c:1097
 asm_call_on_stack+0xf/0x20 arch/x86/entry/entry_64.S:711
 </IRQ>
 __run_on_irqstack arch/x86/include/asm/irq_stack.h:22 [inline]
 run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:48 [inline]
 sysvec_apic_timer_interrupt+0xb9/0x130 arch/x86/kernel/apic/apic.c:1091
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:585
RIP: 0010:rdtsc_ordered arch/x86/include/asm/msr.h:236 [inline]
RIP: 0010:pvclock_clocksource_read+0x91/0x6b0 arch/x86/kernel/pvclock.c:76
Code: 89 44 24 38 48 89 54 24 48 43 0f b6 04 33 84 c0 0f 85 35 01 00 00 42 0f b6 04 32 84 c0 0f 85 80 01 00 00 45 8b 65 00 0f 01 f9 <66> 90 48 89 c3 48 89 d5 48 c1 e5 20 48 8b 44 24 60 42 0f b6 04 30
RSP: 0018:ffffc9000792f488 EFLAGS: 00000246
RAX: 000000006b3418bb RBX: ffffffff89509768 RCX: 0000000000000001
RDX: 0000000000000389 RSI: ffffffff8ad5d05c RDI: ffffffff8ad5d05d
RBP: ffffc9000792f690 R08: ffffffff8ad5d048 R09: ffffffff8ad5d058
R10: ffffffff8ad5d043 R11: 1ffffffff15aba08 R12: 000000000000000e
R13: ffffffff8ad5d040 R14: dffffc0000000000 R15: ffffffff8ad5d050
 kvm_clock_read arch/x86/kernel/kvmclock.c:90 [inline]
 kvm_sched_clock_read+0x15/0x40 arch/x86/kernel/kvmclock.c:102
 paravirt_sched_clock arch/x86/include/asm/paravirt.h:22 [inline]
 sched_clock+0x36/0x40 arch/x86/kernel/tsc.c:252
 sched_clock_cpu+0x18/0x3b0 kernel/sched/clock.c:371
 local_clock include/linux/sched/clock.h:84 [inline]
 cpu_clock_event_update kernel/events/core.c:10207 [inline]
 cpu_clock_event_read+0x17/0x50 kernel/events/core.c:10240
 perf_output_read_group kernel/events/core.c:6693 [inline]
 perf_output_read+0xda4/0x1210 kernel/events/core.c:6732
 perf_output_sample+0x2ae/0x20a0 kernel/events/core.c:6779
 __perf_event_output kernel/events/core.c:7160 [inline]
 perf_event_output_forward+0x10b/0x1c0 kernel/events/core.c:7174
 __perf_event_overflow+0x1b9/0x340 kernel/events/core.c:8746
 do_perf_sw_event kernel/events/core.c:8963 [inline]
 ___perf_sw_event+0x41f/0x550 kernel/events/core.c:8994
 __perf_sw_event+0x13e/0x230 kernel/events/core.c:9006
 handle_page_fault arch/x86/mm/fault.c:1365 [inline]
 exc_page_fault+0x124/0x1f0 arch/x86/mm/fault.c:1418
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:542
RIP: 0010:__clear_user arch/x86/lib/usercopy_64.c:24 [inline]
RIP: 0010:clear_user+0x100/0x170 arch/x86/lib/usercopy_64.c:54
Code: 14 89 be 14 00 00 00 e8 4e fb e4 fd 0f 1f 00 44 89 f8 83 e0 07 49 c1 ef 03 4c 89 f9 4c 89 f7 48 85 c9 74 15 66 0f 1f 44 00 00 <48> c7 07 00 00 00 00 48 83 c7 08 ff c9 75 f1 48 89 c1 85 c9 74 0a
RSP: 0018:ffffc9000792fbc0 EFLAGS: 00010202
RAX: 0000000000000000 RBX: 0000000020b8b380 RCX: 0000000000000070
RDX: ffff8880857aea08 RSI: ffff8880627531e8 RDI: 0000000020b8b000
RBP: 0000000000001000 R08: dffffc0000000000 R09: fffffbfff131a7ee
R10: fffffbfff131a7ee R11: 0000000000000000 R12: 00007ffffffff000
R13: 0000000000001000 R14: 0000000020b8a380 R15: 0000000000000200
 iov_iter_zero+0x1d7/0xe60 lib/iov_iter.c:977
 read_iter_zero+0x89/0x1b0 drivers/char/mem.c:718
 do_iter_readv_writev+0x5b7/0x820 include/linux/fs.h:1902
 do_iter_read+0x16d/0x550 fs/read_write.c:953
 vfs_readv fs/read_write.c:1073 [inline]
 do_readv+0x192/0x330 fs/read_write.c:1110
 do_syscall_64+0x73/0xe0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45c369
Code: 8d b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 5b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffaf496bc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000013
RAX: ffffffffffffffda RBX: 0000000000024f80 RCX: 000000000045c369
RDX: 0000000000000003 RSI: 0000000020000ac0 RDI: 0000000000000006
RBP: 000000000078bf40 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000078bf0c
R13: 00007fffe2f8712f R14: 00007ffaf496c9c0 R15: 000000000078bf0c