rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	1-...!: (10499 ticks this GP) idle=8fa/1/0x4000000000000000 softirq=19758/19758 fqs=6 
	(t=10501 jiffies g=26373 q=157)
rcu: rcu_preempt kthread starved for 10490 jiffies! g26373 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:
rcu_preempt     R  running task    29664    10      2 0x00004000
Call Trace:
 context_switch kernel/sched/core.c:3669 [inline]
 __schedule+0x8e5/0x21e0 kernel/sched/core.c:4418
 schedule+0xd0/0x2a0 kernel/sched/core.c:4493
 schedule_timeout+0x148/0x250 kernel/time/timer.c:1871
 rcu_gp_fqs_loop kernel/rcu/tree.c:1871 [inline]
 rcu_gp_kthread+0xae5/0x1b50 kernel/rcu/tree.c:2041
 kthread+0x3b5/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
NMI backtrace for cpu 1
CPU: 1 PID: 18737 Comm: syz-executor093 Not tainted 5.8.0-rc7-next-20200729-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+0x18f/0x20d lib/dump_stack.c:118
 nmi_cpu_backtrace.cold+0x44/0xd7 lib/nmi_backtrace.c:105
 nmi_trigger_cpumask_backtrace+0x1b3/0x223 lib/nmi_backtrace.c:62
 trigger_single_cpu_backtrace include/linux/nmi.h:165 [inline]
 rcu_dump_cpu_stacks+0x194/0x1cf kernel/rcu/tree_stall.h:318
 print_cpu_stall kernel/rcu/tree_stall.h:551 [inline]
 check_cpu_stall kernel/rcu/tree_stall.h:625 [inline]
 rcu_pending kernel/rcu/tree.c:3626 [inline]
 rcu_sched_clock_irq.cold+0x5b3/0xcbd kernel/rcu/tree.c:2509
 update_process_times+0x25/0x60 kernel/time/timer.c:1709
 tick_sched_handle+0x9b/0x180 kernel/time/tick-sched.c:176
 tick_sched_timer+0x1d1/0x2a0 kernel/time/tick-sched.c:1328
 __run_hrtimer kernel/time/hrtimer.c:1520 [inline]
 __hrtimer_run_queues+0x1d5/0xfc0 kernel/time/hrtimer.c:1584
 hrtimer_interrupt+0x32a/0x930 kernel/time/hrtimer.c:1646
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1079 [inline]
 __sysvec_apic_timer_interrupt+0x142/0x5e0 arch/x86/kernel/apic/apic.c:1096
 asm_call_on_stack+0xf/0x20 arch/x86/entry/entry_64.S:706
 </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+0xb2/0xf0 arch/x86/kernel/apic/apic.c:1090
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:581
RIP: 0010:write_comp_data+0x2f/0x80 kernel/kcov.c:218
Code: 05 66 c3 8d 7e 65 48 8b 34 25 c0 fe 01 00 a9 00 01 ff 00 74 0f f6 c4 01 74 59 8b 86 04 14 00 00 85 c0 74 4f 8b 86 e0 13 00 00 <83> f8 03 75 44 48 8b 86 e8 13 00 00 8b b6 e4 13 00 00 4c 8b 00 48
RSP: 0018:ffffc9000c5d7750 EFLAGS: 00000246
RAX: 0000000000000000 RBX: 0000000000000016 RCX: ffffffff8399a4bc
RDX: 0000000000000016 RSI: ffff888091190080 RDI: 0000000000000005
RBP: 0000000000000000 R08: 0000000000000000 R09: ffff888083e9583f
R10: 0000000000000000 R11: 0000000000000000 R12: ffff888095aea000
R13: 0000000000000000 R14: dffffc0000000000 R15: 0000000000000000
 iov_iter_copy_from_user_atomic+0x69c/0xbe0 lib/iov_iter.c:1001
 generic_perform_write+0x277/0x4f0 mm/filemap.c:3368
 ext4_buffered_write_iter+0x235/0x4a0 fs/ext4/file.c:270
 ext4_file_write_iter+0x1f3/0x1390 fs/ext4/file.c:657
 call_write_iter include/linux/fs.h:1876 [inline]
 do_iter_readv_writev+0x567/0x780 fs/read_write.c:730
 do_iter_write+0x188/0x670 fs/read_write.c:1035
 vfs_iter_write+0x70/0xa0 fs/read_write.c:1076
 iter_file_splice_write+0x721/0xbe0 fs/splice.c:667
 do_splice_from fs/splice.c:736 [inline]
 do_splice+0xbb8/0x17a0 fs/splice.c:1043
 __do_sys_splice fs/splice.c:1318 [inline]
 __se_sys_splice fs/splice.c:1300 [inline]
 __x64_sys_splice+0x198/0x250 fs/splice.c:1300
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x449cd9
Code: e8 3c e6 ff ff 48 83 c4 18 c3 0f 1f 80 00 00 00 00 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 2b 06 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f9d4f1edda8 EFLAGS: 00000246 ORIG_RAX: 0000000000000113
RAX: ffffffffffffffda RBX: 00000000006dfc48 RCX: 0000000000449cd9
RDX: 0000000000000005 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00000000006dfc40 R08: 0000000000010005 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dfc4c
R13: 00007fff8d8dc9ff R14: 00007f9d4f1ee9c0 R15: 0000000000000000
NMI backtrace for cpu 1
CPU: 1 PID: 18737 Comm: syz-executor093 Not tainted 5.8.0-rc7-next-20200729-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:iov_iter_copy_from_user_atomic+0x503/0xbe0 lib/iov_iter.c:1001
Code: 00 49 be 00 00 00 00 00 fc ff df 48 c1 e8 03 4c 01 f0 48 89 44 24 28 e8 bb 9c da fd 48 8b 44 24 28 80 38 00 0f 85 e5 05 00 00 <48> 8b 04 24 44 89 eb 4c 8b 60 18 48 89 d8 48 c1 e0 04 4c 01 e0 48
RSP: 0018:ffffc9000c5d7758 EFLAGS: 00000246
RAX: fffff520018baf9d RBX: 0000000000000016 RCX: ffffffff8399a4bc
RDX: ffff888091190080 RSI: ffffffff8399a315 RDI: 0000000000000005
RBP: 0000000000000000 R08: 0000000000000000 R09: ffff888083e9583f
R10: 0000000000000000 R11: 0000000000000000 R12: ffff888095aea000
R13: 0000000000000000 R14: dffffc0000000000 R15: 0000000000000000
FS:  00007f9d4f1ee700(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000009a296000 CR4: 00000000001506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 generic_perform_write+0x277/0x4f0 mm/filemap.c:3368
 ext4_buffered_write_iter+0x235/0x4a0 fs/ext4/file.c:270
 ext4_file_write_iter+0x1f3/0x1390 fs/ext4/file.c:657
 call_write_iter include/linux/fs.h:1876 [inline]
 do_iter_readv_writev+0x567/0x780 fs/read_write.c:730
 do_iter_write+0x188/0x670 fs/read_write.c:1035
 vfs_iter_write+0x70/0xa0 fs/read_write.c:1076
 iter_file_splice_write+0x721/0xbe0 fs/splice.c:667
 do_splice_from fs/splice.c:736 [inline]
 do_splice+0xbb8/0x17a0 fs/splice.c:1043
 __do_sys_splice fs/splice.c:1318 [inline]
 __se_sys_splice fs/splice.c:1300 [inline]
 __x64_sys_splice+0x198/0x250 fs/splice.c:1300
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x449cd9
Code: e8 3c e6 ff ff 48 83 c4 18 c3 0f 1f 80 00 00 00 00 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 2b 06 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f9d4f1edda8 EFLAGS: 00000246 ORIG_RAX: 0000000000000113
RAX: ffffffffffffffda RBX: 00000000006dfc48 RCX: 0000000000449cd9
RDX: 0000000000000005 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00000000006dfc40 R08: 0000000000010005 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dfc4c
R13: 00007fff8d8dc9ff R14: 00007f9d4f1ee9c0 R15: 0000000000000000