lockdep: Returned to user space with mutex held

[crawfxrd]

lockdep will produce the following warning when reading the proc file.

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WARNING: lock held when returning to user space!
5.0.0-0.rc1.git4.1.fc30.x86_64 #1 Tainted: G           OE    
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cat/1307 is leaving the kernel with locks still held!
1 lock held by cat/1307:
 #0: 000000007c4816ec (&ioctl_mutex){+.+.}, at: dattobd_proc_open+0x17/0x30 [dattobd]