Verifier 0x2001F bugcheck.

[Axel Souchet]

When fixing #2 I didn't realize that acquiring the mutex bumped the IRQL to APC_LEVEL when a bunch of code expects to be running at PASSIVE; verifier detected this a:t runtime

Driver Verifier: Bugcheck initiated with Error Code: 0x2001F Error Message: 'ZwClose should only be called at IRQL = PASSIVE_LEVEL.'
KDTARGET: Refreshing KD connection

*** Fatal System Error: 0x000000c4
                       (0x000000000002001F,0xFFFFF80209086738,0x0000000000000000,0x0000000000000000)

Break instruction exception - code 80000003 (first chance)

A fatal system error has occurred.
Debugger entered on first try; Bugcheck callbacks have not been invoked.

A fatal system error has occurred.

For analysis of this file, run !analyze -v
nt!DbgBreakPointWithStatus:
fffff802`07bd86a0 cc              int     3
kd> kp
 # Child-SP          RetAddr               Call Site
00 ffff9189`5a92e638 fffff802`07cba642     nt!DbgBreakPointWithStatus
01 ffff9189`5a92e640 fffff802`07cb9d32     nt!KiBugCheckDebugBreak+0x12
02 ffff9189`5a92e6a0 fffff802`07bd0a07     nt!KeBugCheck2+0x952
03 ffff9189`5a92eda0 fffff802`09075386     nt!KeBugCheckEx+0x107
04 ffff9189`5a92ede0 fffff802`09073a89     VerifierExt!XdvInitiateBugcheck+0x3a
05 ffff9189`5a92ee20 fffff802`090539cf     VerifierExt!XdvUnifiedBugCheck+0x239
06 ffff9189`5a92ee90 fffff802`09053a16     VerifierExt!SLIC_ZwClose_entry_IrqlZwPassive+0x33
07 ffff9189`5a92eed0 fffff802`08382960     VerifierExt!ZwClose_wrapper+0x36
08 ffff9189`5a92ef20 fffff802`0b56601f     nt!VerifierZwClose+0x10
09 ffff9189`5a92ef50 fffff802`0b565b9b     sic_drv+0x601f