INFO: task hung in rmap_walk

similar bugs (1):
Kernel	Title	Repro	Cause bisect	Fix bisect	Count	Last	Reported	Patched	Status
android-414	INFO: task hung in rmap_walk_file				4	1150d	1170d	0/1	auto-closed as invalid on 2019/10/25 08:51

Bluetooth: hci4 command 0x0406 tx timeout
Bluetooth: hci3 command 0x0406 tx timeout
Bluetooth: hci2 command 0x0406 tx timeout
Bluetooth: hci0 command 0x0406 tx timeout
Bluetooth: hci5 command 0x0406 tx timeout
INFO: task kswapd0:1946 blocked for more than 140 seconds.
      Not tainted 4.14.262-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kswapd0         D28632  1946      2 0x80000000
Call Trace:
 context_switch kernel/sched/core.c:2811 [inline]
 __schedule+0x88b/0x1de0 kernel/sched/core.c:3387
 schedule+0x8d/0x1b0 kernel/sched/core.c:3431
 __rwsem_down_read_failed_common kernel/locking/rwsem-xadd.c:292 [inline]
 rwsem_down_read_failed+0x1e6/0x350 kernel/locking/rwsem-xadd.c:309
 call_rwsem_down_read_failed+0x14/0x30 arch/x86/lib/rwsem.S:94
 __down_read arch/x86/include/asm/rwsem.h:66 [inline]
 down_read+0x44/0x80 kernel/locking/rwsem.c:26
 i_mmap_lock_read include/linux/fs.h:483 [inline]
 rmap_walk_file+0x50e/0x7c0 mm/rmap.c:1828
 rmap_walk+0xc4/0x150 mm/rmap.c:1857
 try_to_unmap+0x243/0x2c0 mm/rmap.c:1673
 shrink_page_list+0x1045/0x2fd0 mm/vmscan.c:1197
 shrink_inactive_list+0x467/0x16c0 mm/vmscan.c:1825
 shrink_list mm/vmscan.c:2177 [inline]
 shrink_node_memcg+0x7a8/0x1190 mm/vmscan.c:2445