Crash Dump Analysis Patterns (Part 44)

Spiking Thread pattern includes normal threads running at PASSIVE_LEVEL or APC_LEVEL IRQL that can be preempted by any other higher priority thread. Therefore, spiking threads are not necessarily ones that were in RUNNING state when the memory dump was saved. They consumed much CPU and this is reflected in their User and Kernel time values. The pattern also includes threads running at DISPATCH_LEVEL and higher IRQL. These threads cannot be preempted by another thread so they usually remain in RUNNING state all the time unless they lower their IRQL. Some of them I’ve seen were trying to acquire a spinlock and I decided to create another more specialized pattern and call it Dispatch Level Spin. We would see it when a spinlock for some data structure wasn’t released or was corrupt and some thread tries to acquire it and enters endless spinning loop unless interrupted by higher IRQL interrupt. These infinite loops can also happen due to software defects in code running at dispatch level or higher IRQL.

Let’s look at one example. The following running thread was interrupted by keyboard interrupt apparently to save Manual Dump. We see that it spent almost 11 minutes in kernel:

0: kd> !thread
THREAD 830c07c0  Cid 0588.0528  Teb: 7ffa3000 Win32Thread: e29546a8 RUNNING on processor 0
IRP List:
    86163008: (0006,01d8) Flags: 00000900  Mdl: 84f156c0
Not impersonating
DeviceMap                 e257b7c8
Owning Process            831ec608       Image:         MyApp.EXE
Wait Start TickCount      122850         Ticks: 40796 (0:00:10:37.437)
Context Switch Count      191                 LargeStack
UserTime                  00:00:00.000
KernelTime                00:10:37.406
Win32 Start Address MyApp!ThreadImpersonation (0×35f76821)
Start Address kernel32!BaseThreadStartThunk (0×7c810659)
Stack Init a07bf000 Current a07beca0 Base a07bf000 Limit a07bb000 Call 0
Priority 11 BasePriority 8 PriorityDecrement 2 DecrementCount 16
ChildEBP RetAddr
a07be0f8 f77777fa nt!KeBugCheckEx+0×1b
a07be114 f7777032 i8042prt!I8xProcessCrashDump+0×237
a07be15c 805448e5 i8042prt!I8042KeyboardInterruptService+0×21c
a07be15c 806e4a37 nt!KiInterruptDispatch+0×45 (FPO: [0,2] TrapFrame @ a07be180)

a07be220 a1342755 hal!KeAcquireInStackQueuedSpinLock+0×47
a07be220 a1342755 MyDriver!RcvData+0×98

To see the code and context we switch to the trap frame and disassemble the interrupted function:

1: kd> .trap a07be180
ErrCode = 00000000
eax=a07be200 ebx=a07be228 ecx=831dabf5 edx=a07beb94 esi=831d02a8 edi=831dabd8
eip=806e4a37 esp=a07be1f4 ebp=a07be220 iopl=0 nv up ei pl nz na po nc
cs=0008 ss=0010 ds=0000 es=0000 fs=0000 gs=0000 efl=00000202
806e4a37 ebf3            jmp     hal!KeAcquireInStackQueuedSpinLock+0×3c (806e4a2c)

1: kd> uf hal!KeAcquireInStackQueuedSpinLock
806e49f0 mov     eax,dword ptr ds:[FFFE0080h]
806e49f5 shr     eax,4
806e49f8 mov     al,byte ptr hal!HalpVectorToIRQL (806ef218)[eax]
806e49fe mov     dword ptr ds:[0FFFE0080h],41h
806e4a08 mov     byte ptr [edx+8],al
806e4a0b mov     dword ptr [edx+4],ecx
806e4a0e mov     dword ptr [edx],0
806e4a14 mov     eax,edx
806e4a16 xchg    edx,dword ptr [ecx]
806e4a18 cmp     edx,0
806e4a1b jne     hal!KeAcquireInStackQueuedSpinLock+0x34 (806e4a24)

806e4a1d or      ecx,2
806e4a20 mov     dword ptr [eax+4],ecx

806e4a23 ret

806e4a24 or      ecx,1
806e4a27 mov     dword ptr [eax+4],ecx
806e4a2a mov     dword ptr [edx],eax

806e4a2c test    dword ptr [eax+4],1
806e4a33 je      hal!KeAcquireInStackQueuedSpinLock+0×33 (806e4a23)

806e4a35 pause
806e4a37 jmp     hal!KeAcquireInStackQueuedSpinLock+0×3c (806e4a2c)

JMP instruction transfers execution to the code that tests the first bit at [EAX+4] address. If it isn’t set it falls through to the same JMP instruction. We know the value of EAX from the trap frame so we can dereference that address:

1: kd> dyd eax+4 l1
           3          2          1          0
          10987654 32109876 54321098 76543210
          -------- -------- -------- --------
a07be204  10000011 00011101 10101011 11110101  831dabf5

The value is odd: the first leftmost bit is set. Therefore the code will loop indefinitely unless a different thread running on another processor clears that bit. However the second processor is idle:

0: kd> ~0s

0: kd> k
ChildEBP RetAddr
f794cd54 00000000 nt!KiIdleLoop+0x14

Seems we have a problem. We need to examine MyDriver.sys code to understand how it uses queued spinlocks.

Note: In addition to user-defined there are internal system queued spinlocks you can check by using !qlocks WinDbg command. 

- Dmitry Vostokov @ -

3 Responses to “Crash Dump Analysis Patterns (Part 44)”

  1. Crash Dump Analysis » Blog Archive » Crash Dump Analysis Patterns (Part 68) Says:

    […] higher priority thread (Thread Starvation pattern) or loops at dispatch level IRQL (Dispatch Level Spin pattern). Therefore I call this pattern Affine […]

  2. Software Generalist » Blog Archive » Reading Notebook: 18-Jan-09 Says:

    […] and blocks threads (pp. 63 - 64) - See my real life patterns Dispatch Level Spin and Affine Thread and […]

  3. Crash Dump Analysis » Blog Archive » Icons for Memory Dump Analysis Patterns (Part 76) Says:

    […] Experts Magazine Online Today we introduce an icon for Dispatch Level Spin […]

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