WARNING in check_flush_dependency

Hello,

syzbot hit the following crash on upstream commit
0d665e7b109d512b7cae3ccef6e8654714887844 (Fri Jan 19 12:49:24 2018 +0000)
mm, page_vma_mapped: Drop faulty pointer arithmetics in check_pte()

So far this crash happened 23 times on net-next, upstream.
C reproducer is attached.
syzkaller reproducer is attached.
Raw console output is attached.
compiler: gcc (GCC) 7.1.1 20170620
.config is attached.
user-space arch: i386

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Reported-by: syzbot+41cdaf4232c50e658934@syzkaller.appspotmail.com
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------------[ cut here ]------------
workqueue: WQ_MEM_RECLAIM hwsim_wq:destroy_radio is flushing !WQ_MEM_RECLAIM events_highpri:flush_backlog
WARNING: CPU: 0 PID: 3706 at kernel/workqueue.c:2439 check_flush_dependency+0x239/0x380 kernel/workqueue.c:2435
Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 3706 Comm: kworker/0:5 Not tainted 4.15.0-rc9+ #184
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: hwsim_wq destroy_radio
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:53
 panic+0x1e4/0x41c kernel/panic.c:183
 __warn+0x1dc/0x200 kernel/panic.c:547
 report_bug+0x211/0x2d0 lib/bug.c:184
 fixup_bug.part.11+0x37/0x80 arch/x86/kernel/traps.c:178
 fixup_bug arch/x86/kernel/traps.c:247 [inline]
 do_error_trap+0x2d7/0x3e0 arch/x86/kernel/traps.c:296
 do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:315
 invalid_op+0x22/0x40 arch/x86/entry/entry_64.S:1096
RIP: 0010:check_flush_dependency+0x239/0x380 kernel/workqueue.c:2435
RSP: 0018:ffff8801d7c2ed78 EFLAGS: 00010082
RAX: dffffc0000000008 RBX: ffff8801d42ca540 RCX: ffffffff8159ebae
RDX: 0000000000000000 RSI: 1ffff1003af85d6a RDI: ffff8801d842eb80
RBP: ffff8801d7c2eda8 R08: 0000000000000000 R09: 1ffff1003af85d3c
R10: ffff8801d7c2ec70 R11: 0000000000000005 R12: ffff8801dac14b70
R13: ffffffff8437cb60 R14: ffff8801c3368d00 R15: 0000000000000000
 start_flush_work kernel/workqueue.c:2827 [inline]
 flush_work+0x2f7/0x8f0 kernel/workqueue.c:2870
 flush_all_backlogs net/core/dev.c:4683 [inline]
 rollback_registered_many+0x672/0xdf0 net/core/dev.c:7241
 unregister_netdevice_many.part.110+0x87/0x420 net/core/dev.c:8304
 unregister_netdevice_many+0xbb/0x100 net/core/dev.c:8303
 ieee80211_remove_interfaces+0x4b3/0x990 net/mac80211/iface.c:1960
 ieee80211_unregister_hw+0x4c/0x270 net/mac80211/main.c:1181
 mac80211_hwsim_del_radio+0x1ee/0x3b0 drivers/net/wireless/mac80211_hwsim.c:2789
 destroy_radio+0x9d/0x100 drivers/net/wireless/mac80211_hwsim.c:3339
 process_one_work+0xbbf/0x1b10 kernel/workqueue.c:2113
 worker_thread+0x223/0x1990 kernel/workqueue.c:2247
 kthread+0x33c/0x400 kernel/kthread.c:238
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:541
Shutting down cpus with NMI
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


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