rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	1-...!: (1 GPs behind) idle=7e2/1/0x4000000000000002 softirq=17807/17808 fqs=1 
	(t=10502 jiffies g=10761 q=678)
rcu: rcu_preempt kthread starved for 7746 jiffies! g10761 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=0
rcu: RCU grace-period kthread stack dump:
rcu_preempt     I29384    10      2 0x80004000
Call Trace:
 schedule+0xd0/0x2a0 kernel/sched/core.c:4154
 schedule_timeout+0x474/0xba0 kernel/time/timer.c:1895
 rcu_gp_fqs_loop kernel/rcu/tree.c:1658 [inline]
 rcu_gp_kthread+0x9d9/0x17d0 kernel/rcu/tree.c:1818
 kthread+0x357/0x430 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
NMI backtrace for cpu 1
CPU: 1 PID: 9703 Comm: syz-executor.4 Not tainted 5.6.0-rc5-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+0x188/0x20d lib/dump_stack.c:118
 nmi_cpu_backtrace.cold+0x70/0xb1 lib/nmi_backtrace.c:101
 nmi_trigger_cpumask_backtrace+0x231/0x27e lib/nmi_backtrace.c:62
 trigger_single_cpu_backtrace include/linux/nmi.h:164 [inline]
 rcu_dump_cpu_stacks+0x169/0x1b3 kernel/rcu/tree_stall.h:254
 print_cpu_stall kernel/rcu/tree_stall.h:475 [inline]
 check_cpu_stall kernel/rcu/tree_stall.h:549 [inline]
 rcu_pending kernel/rcu/tree.c:3030 [inline]
 rcu_sched_clock_irq.cold+0x518/0xc55 kernel/rcu/tree.c:2276
 update_process_times+0x25/0x60 kernel/time/timer.c:1726
 tick_sched_handle+0x9b/0x180 kernel/time/tick-sched.c:171
 tick_sched_timer+0x4e/0x140 kernel/time/tick-sched.c:1314
 __run_hrtimer kernel/time/hrtimer.c:1517 [inline]
 __hrtimer_run_queues+0x32c/0xdd0 kernel/time/hrtimer.c:1579
 hrtimer_interrupt+0x312/0x770 kernel/time/hrtimer.c:1641
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1119 [inline]
 smp_apic_timer_interrupt+0x15b/0x600 arch/x86/kernel/apic/apic.c:1144
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:829
 </IRQ>
RIP: 0010:lock_is_held include/linux/lockdep.h:361 [inline]
RIP: 0010:rcu_read_lock_sched_held+0x8b/0xd0 kernel/rcu/update.c:121
Code: 24 20 48 ba 00 00 00 00 00 fc ff df 48 c7 04 13 00 00 00 00 48 8b 4c 24 58 65 48 33 0c 25 28 00 00 00 75 3a 48 83 c4 60 5b c3 <be> ff ff ff ff 48 c7 c7 40 cc 7a 89 e8 a4 39 f9 ff 41 89 c0 b8 01
RSP: 0018:ffffc900043eefc0 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
RAX: 0000000000000000 RBX: 1ffff9200087ddf8 RCX: 0000000000000000
RDX: 0000000080000001 RSI: ffffffff8392430f RDI: 0000000000000001
RBP: 0000000000000000 R08: ffff888047190100 R09: ffffed1015ce7074
R10: ffffed1015ce7073 R11: ffff8880ae73839b R12: 0000000000000000
R13: dffffc0000000000 R14: ffff888091cf6f18 R15: 000000000000042b
 trace_block_touch_buffer include/trace/events/block.h:45 [inline]
 touch_buffer fs/buffer.c:62 [inline]
 __find_get_block+0xb95/0xe90 fs/buffer.c:1340
 __getblk_gfp+0x33/0xae0 fs/buffer.c:1358
 sb_getblk include/linux/buffer_head.h:325 [inline]
 __ext4_get_inode_loc+0x3fe/0x1320 fs/ext4/inode.c:4263
 ext4_reserve_inode_write+0xc6/0x230 fs/ext4/inode.c:5609
 ext4_mark_inode_dirty+0x174/0x900 fs/ext4/inode.c:5775
 ext4_dirty_inode+0xe7/0x120 fs/ext4/inode.c:5814
 __mark_inode_dirty+0x65e/0x1350 fs/fs-writeback.c:2258
 mark_inode_dirty include/linux/fs.h:2183 [inline]
 generic_write_end+0x2f4/0x3d0 fs/buffer.c:2199
 ext4_da_write_end+0x217/0xbd0 fs/ext4/inode.c:3092
 generic_perform_write+0x2c0/0x4e0 mm/filemap.c:3298
 ext4_buffered_write_iter+0x1f7/0x450 fs/ext4/file.c:270
 ext4_file_write_iter+0x1ec/0x13f0 fs/ext4/file.c:642
 call_write_iter include/linux/fs.h:1901 [inline]
 do_iter_readv_writev+0x59c/0x840 fs/read_write.c:693
 do_iter_write fs/read_write.c:998 [inline]
 do_iter_write+0x185/0x600 fs/read_write.c:979
 vfs_iter_write+0x70/0xa0 fs/read_write.c:1039
 iter_file_splice_write+0x684/0xb00 fs/splice.c:760
 do_splice_from fs/splice.c:863 [inline]
 direct_splice_actor+0x115/0x160 fs/splice.c:1037
 splice_direct_to_actor+0x38c/0x980 fs/splice.c:992
 do_splice_direct+0x1a8/0x270 fs/splice.c:1080
 do_sendfile+0x549/0xc40 fs/read_write.c:1520
 __do_sys_sendfile64 fs/read_write.c:1575 [inline]
 __se_sys_sendfile64 fs/read_write.c:1567 [inline]
 __x64_sys_sendfile64+0x149/0x210 fs/read_write.c:1567
 do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45c4a9
Code: ad 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 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fb836d7ec78 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007fb836d7f6d4 RCX: 000000000045c4a9
RDX: 00000000200001c0 RSI: 0000000000000004 RDI: 0000000000000004
RBP: 000000000076bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 00008080fffffffe R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000000008d1 R14: 00000000004cb3b0 R15: 000000000076bf2c