syzbot

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P3561/1:b..l P4403/1:b..l
	(detected by 0, t=10502 jiffies, g=8309, q=95)
task:kworker/u4:6    state:R  running task     stack:26504 pid: 4403 ppid:     2 flags:0x00004000
Workqueue: ext4-rsv-conversion ext4_end_io_rsv_work
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5049 [inline]
 __schedule+0x11bb/0x4390 kernel/sched/core.c:6395
 preempt_schedule_irq+0xb1/0x150 kernel/sched/core.c:6799
 irqentry_exit+0x63/0x70 kernel/entry/common.c:432
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:instrument_atomic_read include/linux/instrumented.h:71 [inline]
RIP: 0010:atomic_read include/linux/atomic/atomic-instrumented.h:27 [inline]
RIP: 0010:lock_page_memcg+0x20c/0x410 mm/memcontrol.c:2062
Code: ff 48 c7 44 24 40 00 00 00 00 9c 8f 44 24 40 f6 44 24 41 02 0f 85 f9 00 00 00 f7 c3 00 02 00 00 74 01 fb 4d 8d af 80 10 00 00 <4c> 89 ef be 04 00 00 00 e8 77 95 fb ff 4c 89 e8 48 c1 e8 03 48 b9
RSP: 0018:ffffc90003cbf820 EFLAGS: 00000206
RAX: c282985021c2c300 RBX: 0000000000000286 RCX: c282985021c2c300
RDX: dffffc0000000000 RSI: ffffffff8a0b1820 RDI: ffffffff8a59a480
RBP: ffffc90003cbf8f0 R08: dffffc0000000000 R09: fffffbfff1ff7833
R10: fffffbfff1ff7833 R11: 1ffffffff1ff7832 R12: ffff888016a7c670
R13: ffff888016a7d080 R14: ffffea0001cc8778 R15: ffff888016a7c000
 test_clear_page_writeback+0x93/0xd20 mm/page-writeback.c:2800
 end_page_writeback+0x282/0x660 mm/filemap.c:1603
 ext4_finish_bio+0x747/0x8b0 fs/ext4/page-io.c:145
 ext4_release_io_end+0xef/0x2c0 fs/ext4/page-io.c:160
 ext4_end_io_end fs/ext4/page-io.c:194 [inline]
 ext4_do_flush_completed_IO fs/ext4/page-io.c:259 [inline]
 ext4_end_io_rsv_work+0x4ee/0x600 fs/ext4/page-io.c:273
 process_one_work+0x863/0x1000 kernel/workqueue.c:2310
 worker_thread+0xaa8/0x12a0 kernel/workqueue.c:2457
 kthread+0x436/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>
task:udevd           state:R  running task     stack:25352 pid: 3561 ppid:     1 flags:0x00004002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5049 [inline]
 __schedule+0x11bb/0x4390 kernel/sched/core.c:6395
 preempt_schedule_notrace+0xca/0x110 kernel/sched/core.c:6650
 preempt_schedule_notrace_thunk+0x16/0x18 arch/x86/entry/thunk_64.S:35
 rcu_is_watching+0x72/0xa0 kernel/rcu/tree.c:1124
 rcu_read_lock include/linux/rcupdate.h:740 [inline]
 dput+0x4e/0x1a0 fs/dcache.c:879
 step_into+0x31d/0xd00 fs/namei.c:1815
 open_last_lookups fs/namei.c:3555 [inline]
 path_openat+0x163f/0x2f30 fs/namei.c:3739
 do_filp_open+0x1b3/0x3e0 fs/namei.c:3769
 do_sys_openat2+0x142/0x4a0 fs/open.c:1253
 do_sys_open fs/open.c:1269 [inline]
 __do_sys_openat fs/open.c:1285 [inline]
 __se_sys_openat fs/open.c:1280 [inline]
 __x64_sys_openat+0x135/0x160 fs/open.c:1280
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f42b4ca6c3a
RSP: 002b:00007ffcabd53688 EFLAGS: 00000206 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 000055c719778eb0 RCX: 00007f42b4ca6c3a
RDX: 0000000000090800 RSI: 000055c7195ee410 RDI: 00000000ffffff9c
RBP: 000055c7195ee410 R08: 0000000000000000 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000206 R12: 000055c7195ff7b0
R13: 00000000000000ff R14: 000055c6ddf32be0 R15: 00007ffcabd53910
 </TASK>
rcu: rcu_preempt kthread starved for 10562 jiffies! g8309 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
rcu: 	Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
rcu: RCU grace-period kthread stack dump:
task:rcu_preempt     state:R  running task     stack:27464 pid:   15 ppid:     2 flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5049 [inline]
 __schedule+0x11bb/0x4390 kernel/sched/core.c:6395
 preempt_schedule_common+0x82/0xd0 kernel/sched/core.c:6571
 preempt_schedule+0xa7/0xb0 kernel/sched/core.c:6596
 preempt_schedule_thunk+0x16/0x18 arch/x86/entry/thunk_64.S:34
 __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:161 [inline]
 _raw_spin_unlock_irqrestore+0xf6/0x100 kernel/locking/spinlock.c:194
 rcu_gp_fqs_loop+0x2b7/0x11b0 kernel/rcu/tree.c:1972
 rcu_gp_kthread+0x98/0x350 kernel/rcu/tree.c:2145
 kthread+0x436/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at native_safe_halt arch/x86/include/asm/irqflags.h:51 [inline]
NMI backtrace for cpu 1 skipped: idling at arch_safe_halt arch/x86/include/asm/irqflags.h:89 [inline]
NMI backtrace for cpu 1 skipped: idling at default_idle+0xb/0x10 arch/x86/kernel/process.c:729