syzbot

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P4189/1:b..l
	(detected by 0, t=10502 jiffies, g=6621, q=154)
task:syz-executor    state:R  running task     stack:21424 pid: 4189 ppid:  4187 flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5049 [inline]
 __schedule+0x11ef/0x43c0 kernel/sched/core.c:6395
 preempt_schedule_irq+0xbb/0x160 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:__sanitizer_cov_trace_pc+0x0/0x60 kernel/kcov.c:202
Code: 66 2e 0f 1f 84 00 00 00 00 00 53 48 89 fb e8 17 00 00 00 48 8b 3d d0 bd 10 0c 48 89 de 5b e9 27 55 44 00 00 00 cc cc 00 00 cc <48> 8b 04 24 65 48 8b 0d 24 3b 89 7e 65 8b 15 25 3b 89 7e 81 e2 00
RSP: 0018:ffffc90002eef720 EFLAGS: 00000202
RAX: ffffffff8408ea00 RBX: 1ffff920005ddf0c RCX: ffff88807bc63b00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000002
RBP: dffffc0000000000 R08: ffff88807bc63b80 R09: 0000000000000002
R10: 0000000000000003 R11: 0000000000000000 R12: ffffc90002eef860
R13: 0000000000000000 R14: ffffea0001d266c0 R15: 0000000000000002
 xas_descend+0x210/0x3b0 lib/xarray.c:207
 xas_load lib/xarray.c:240 [inline]
 xas_find+0x1e0/0xab0 lib/xarray.c:1249
 find_get_entry mm/filemap.c:1978 [inline]
 find_lock_entries+0x19e/0xd70 mm/filemap.c:2092
 shmem_undo_range+0x29a/0x1930 mm/shmem.c:943
 shmem_truncate_range mm/shmem.c:1063 [inline]
 shmem_evict_inode+0x220/0xa40 mm/shmem.c:1145
 evict+0x4c9/0x8d0 fs/inode.c:647
 do_unlinkat+0x3e7/0x710 fs/namei.c:4363
 __do_sys_unlink fs/namei.c:4404 [inline]
 __se_sys_unlink fs/namei.c:4402 [inline]
 __x64_sys_unlink+0x45/0x50 fs/namei.c:4402
 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: 0033:0x7f7d1175cf47
RSP: 002b:00007ffc977fef98 EFLAGS: 00000206 ORIG_RAX: 0000000000000057
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f7d1175cf47
RDX: 00007ffc977fefc0 RSI: 00007ffc977ff050 RDI: 00007ffc977ff050
RBP: 00007ffc977ff050 R08: 00007ffc97800050 R09: 00000000ffffffff
R10: 0000000000000100 R11: 0000000000000206 R12: 00007ffc978000e0
R13: 00007f7d117f31ca R14: 0000000000013a1c R15: 00007ffc97800120
 </TASK>
rcu: rcu_preempt kthread starved for 10479 jiffies! g6621 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:27608 pid:   15 ppid:     2 flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5049 [inline]
 __schedule+0x11ef/0x43c0 kernel/sched/core.c:6395
 schedule+0x11b/0x1e0 kernel/sched/core.c:6478
 schedule_timeout+0x184/0x2d0 kernel/time/timer.c:2117
 rcu_gp_fqs_loop+0x2be/0x11d0 kernel/rcu/tree.c:1972
 rcu_gp_kthread+0x9b/0x370 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