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WARNING: lock held when returning to user space!
5.5.0-rc6-next-20200116-syzkaller #0 Not tainted
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syz-executor.0/10594 is leaving the kernel with locks still held!
1 lock held by syz-executor.0/10594:
 #0: ffff888098c1e748 (&tfile->napi_mutex){+.+.}, at: tun_get_user+0x1604/0x3fc0 drivers/net/tun.c:1835
syz-executor.0 (10594) used greatest stack depth: 22392 bytes left