syzbot

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P6907/1:b..l
	(detected by 0, t=10502 jiffies, g=30273, q=129)
task:syz.1.767       state:R  running task     stack:24408 pid: 6907 ppid:  3569 flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5027 [inline]
 __schedule+0x12c4/0x45b0 kernel/sched/core.c:6373
 preempt_schedule_irq+0xf7/0x1c0 kernel/sched/core.c:6777
 irqentry_exit+0x53/0x80 kernel/entry/common.c:432
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:638
RIP: 0010:debug_lockdep_rcu_enabled+0x28/0x30 kernel/rcu/update.c:280
Code: cc cc 31 c0 83 3d ab 0e b5 03 00 74 1d 83 3d 22 41 b5 03 00 74 14 65 48 8b 0d 94 1c ce 75 31 c0 83 b9 ec 0a 00 00 00 0f 94 c0 <c3> cc cc cc cc cc cc cc 41 56 53 89 fb e8 d6 0d 00 00 41 89 c6 83
RSP: 0018:ffffc900035172c8 EFLAGS: 00000246
RAX: 0000000000000001 RBX: ffff88805f024188 RCX: ffff888023fc1dc0
RDX: ffffc90004280000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffff88805f0241d0 R08: ffffffff84303186 R09: fffffbfff20e2419
R10: 0000000000000000 R11: dffffc0000000001 R12: ffffc900035173c0
R13: ffff888063302942 R14: ffffc900035173d8 R15: 1ffff920006a2e7b
 xa_head include/linux/xarray.h:1166 [inline]
 xas_start+0x1f8/0x7b0 lib/xarray.c:188
 xas_load+0x28/0x140 lib/xarray.c:233
 mapping_get_entry mm/filemap.c:1826 [inline]
 pagecache_get_page+0x20f/0x1010 mm/filemap.c:1894
 shmem_getpage_gfp+0x36c/0x3190 mm/shmem.c:1841
 shmem_fault+0x1d7/0x700 mm/shmem.c:2118
 __do_fault+0x139/0x340 mm/memory.c:3898
 do_read_fault mm/memory.c:4234 [inline]
 do_fault mm/memory.c:4362 [inline]
 handle_pte_fault mm/memory.c:4620 [inline]
 __handle_mm_fault mm/memory.c:4755 [inline]
 handle_mm_fault+0x376f/0x5960 mm/memory.c:4853
 faultin_page mm/gup.c:976 [inline]
 __get_user_pages+0x4ed/0x11d0 mm/gup.c:1197
 populate_vma_page_range+0x215/0x2a0 mm/gup.c:1529
 __mm_populate+0x2a5/0x4a0 mm/gup.c:1638
 mm_populate include/linux/mm.h:2632 [inline]
 vm_mmap_pgoff+0x22b/0x2d0 mm/util.c:556
 ksys_mmap_pgoff+0x13e/0x780 mm/mmap.c:1624
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f76b4251ff9
RSP: 002b:00007f76b26a9038 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007f76b440a058 RCX: 00007f76b4251ff9
RDX: b635773f06ebbeee RSI: 0000000000b36000 RDI: 0000000020000000
RBP: 00007f76b42c4296 R08: ffffffffffffffff R09: 0000000000000000
R10: 0000000000008031 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000001 R14: 00007f76b440a058 R15: 00007ffe68a4d3d8
 </TASK>
rcu: rcu_preempt kthread starved for 9860 jiffies! g30273 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:27032 pid:   15 ppid:     2 flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5027 [inline]
 __schedule+0x12c4/0x45b0 kernel/sched/core.c:6373
 schedule+0x11b/0x1f0 kernel/sched/core.c:6456
 schedule_timeout+0x1b9/0x300 kernel/time/timer.c:1914
 rcu_gp_fqs_loop+0x2bf/0x1080 kernel/rcu/tree.c:1972
 rcu_gp_kthread+0xa4/0x360 kernel/rcu/tree.c:2145
 kthread+0x3f6/0x4f0 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 acpi_safe_halt drivers/acpi/processor_idle.c:108 [inline]
NMI backtrace for cpu 1 skipped: idling at acpi_idle_do_entry+0x10f/0x340 drivers/acpi/processor_idle.c:562