syzbot

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P37/1:b..l
rcu: 	(detected by 1, t=10502 jiffies, g=247757, q=604 ncpus=2)
task:khugepaged      state:R  running task     stack:27360 pid:37    tgid:37    ppid:2      flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5188 [inline]
 __schedule+0xe37/0x5490 kernel/sched/core.c:6529
 preempt_schedule_irq+0x51/0x90 kernel/sched/core.c:6851
 irqentry_exit+0x36/0x90 kernel/entry/common.c:354
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
RIP: 0010:is_zero_pfn include/linux/pgtable.h:1568 [inline]
RIP: 0010:__collapse_huge_page_copy_succeeded mm/khugepaged.c:719 [inline]
RIP: 0010:__collapse_huge_page_copy mm/khugepaged.c:825 [inline]
RIP: 0010:collapse_huge_page+0x1b04/0x30a0 mm/khugepaged.c:1213
Code: 89 ee e8 3f 0d 9d ff 48 85 ed 0f 85 00 03 00 00 e8 c1 0a 9d ff 31 db e8 ba 0a 9d ff 48 8b 44 24 28 48 c1 e8 03 42 80 3c 30 00 <0f> 85 a6 0f 00 00 4c 8b 2d 1f 90 25 0e 48 89 de 4c 89 ef e8 44 0c
RSP: 0018:ffffc90000ad7968 EFLAGS: 00000246
RAX: 1ffffffff2025fb4 RBX: 0000000000000000 RCX: ffffffff81ed6d51
RDX: ffff8880186dda00 RSI: ffffffff81ed6d66 RDI: 0000000000000007
RBP: 0000000000000000 R08: 0000000000000007 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff88805b58eef8
R13: ffff88806af30e68 R14: dffffc0000000000 R15: ffffc90000ad7b00
 hpage_collapse_scan_pmd+0xafe/0x11b0 mm/khugepaged.c:1419
 khugepaged_scan_mm_slot mm/khugepaged.c:2427 [inline]
 khugepaged_do_scan mm/khugepaged.c:2514 [inline]
 khugepaged+0x1139/0x1600 mm/khugepaged.c:2570
 kthread+0x2c1/0x3a0 kernel/kthread.c:389
 ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>
rcu: rcu_preempt kthread starved for 10520 jiffies! g247757 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:
task:rcu_preempt     state:R  running task     stack:27632 pid:17    tgid:17    ppid:2      flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5188 [inline]
 __schedule+0xe37/0x5490 kernel/sched/core.c:6529
 __schedule_loop kernel/sched/core.c:6606 [inline]
 schedule+0xe7/0x350 kernel/sched/core.c:6621
 schedule_timeout+0x136/0x2a0 kernel/time/timer.c:2581
 rcu_gp_fqs_loop+0x1eb/0xb00 kernel/rcu/tree.c:2034
 rcu_gp_kthread+0x271/0x380 kernel/rcu/tree.c:2236
 kthread+0x2c1/0x3a0 kernel/kthread.c:389
 ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at native_safe_halt arch/x86/include/asm/irqflags.h:48 [inline]
NMI backtrace for cpu 0 skipped: idling at arch_safe_halt arch/x86/include/asm/irqflags.h:106 [inline]
NMI backtrace for cpu 0 skipped: idling at acpi_safe_halt+0x1a/0x20 drivers/acpi/processor_idle.c:111