The !deadlock extension displays information about deadlocks collected by the Deadlock Detection option of Driver Verifier.
!deadlock !deadlock 1
Windows XP and later
For information about Driver Verifier, see the Windows Driver Kit (WDK) documentation.
This extension will only provide useful information if Driver Verifier's Deadlock Detection option has detected a lock hierarchy violation and issued bug check 0xC4 (DRIVER_VERIFIER_DETECTED_VIOLATION).
Without any arguments, the !deadlock extension causes the basic lock hierarchy topology to be displayed. If the problem is not a simple cyclical deadlock, this command will describe the situation that has occurred.
The !deadlock 1 extension causes stack traces to be displayed. The stacks displayed will be the ones active at the time the locks were acquired.
Here is an example:
0:kd> !deadlock Deadlock detected (2 resources in 2 threads): Thread 0: A B Thread 1: B A Where: Thread 0 = 8d3ba030 Thread 1 = 8d15c030 Lock A = bba2af30 Type 'Spinlock' Lock B = dummy!GlobalLock Type 'Spinlock'
This tells you which threads and which locks are involved. However, it is intended to be a summary and may not be enough information to adequately debug the situation.
Use !deadlock 1 to print out the contents of the call stacks at the time that each lock participating in the deadlock was acquired. Because these are run-time stack traces, they will be more complete if a checked build is being used. Checked builds were available on older versions of Windows before Windows 10, version 1803. On a free build, they may be truncated after as little as one line.
0:kd> !deadlock 1 Deadlock detected (2 resources in 2 threads): Thread 0 (8D14F750) took locks in the following order: Lock A -- b7906f30 (Spinlock) Stack: dummy!DummyActivateVcComplete+0x63 dummy!dummyOpenVcChannels+0x2E1 dummy!DummyAllocateRecvBufferComplete+0x436 dummy!DummyAllocateComplete+0x55 NDIS!ndisMQueuedAllocateSharedHandler+0xC9 NDIS!ndisWorkerThread+0xEE Lock B -- dummy!GlobalLock (Spinlock) Stack: dummy!dummyQueueRecvBuffers+0x2D dummy!DummyActivateVcComplete+0x90 dummy!dummyOpenVcChannels+0x2E1 dummy!DummyAllocateRecvBufferComplete+0x436 dummy!DummyAllocateComplete+0x55 Thread 1 (8D903030) took locks in the following order: Lock B -- dummy!GlobalLock (Spinlock) Stack: dummy!dummyRxInterruptOnCompletion+0x25D dummy!DummyHandleInterrupt+0x32F NDIS!ndisMDpcX+0x3C ntkrnlpa!KiRetireDpcList+0x5D Lock A -- b7906f30 (Spinlock) Stack: << Current stack >>
With this information, you have almost everything you need, except the current stack:
0: kd> k ChildEBP RetAddr f78aae6c 80664c58 ntkrnlpa!DbgBreakPoint f78aae74 8066523f ntkrnlpa!ViDeadlockReportIssue+0x2f f78aae9c 806665df ntkrnlpa!ViDeadlockAnalyze+0x253 f78aaee8 8065d944 ntkrnlpa!VfDeadlockAcquireResource+0x20b f78aaf08 bfd6df46 ntkrnlpa!VerifierKeAcquireSpinLockAtDpcLevel+0x44 f78aafa4 b1bf2d2d dummy!dummyRxInterruptOnCompletion+0x2b5 f78aafc4 bfde9d8c dummy!DummyHandleInterrupt+0x32f f78aafd8 804b393b NDIS!ndisMDpcX+0x3c f78aaff4 804b922b ntkrnlpa!KiRetireDpcList+0x5d
From this you can see which locks were involved and where they were acquired. This should be enough information for you to debug the deadlock. If the source code is available, you can use the debugger to see exactly where the problem occurred:
0: kd> .lines Line number information will be loaded 0: kd> u dummy!DummyActivateVcComplete+0x63 l1 dummy!DummyActivateVcComplete+63 [d:\nt\drivers\dummy\vc.c @ 2711]: b1bfe6c9 837d0c00 cmp dword ptr [ebp+0xc],0x0 0: kd> u dummy!dummyQueueRecvBuffers+0x2D l1 dummy!dummyQueueRecvBuffers+2d [d:\nt\drivers\dummy\receive.c @ 2894]: b1bf4e39 807d0c01 cmp byte ptr [ebp+0xc],0x1 0: kd> u dummy!dummyRxInterruptOnCompletion+0x25D l1 dummy!dummyRxInterruptOnCompletion+25d [d:\nt\drivers\dummy\receive.c @ 1424]: b1bf5d05 85f6 test esi,esi 0: kd> u dummy!dummyRxInterruptOnCompletion+0x2b5 l1 dummy!dummyRxInterruptOnCompletion+2b5 [d:\nt\drivers\dummy\receive.c @ 1441]: b1bf5d5d 8b4648 mov eax,[esi+0x48]
Now you know the name of the source file and the line number where the acquisition took place. In this case, the source files will show that the threads behaved as follows:
Thread 1: DummyActivateVcComplete took the dummy miniport lock. It then called dummyQueueRecvBuffers, which took the dummy global lock.
Thread 2: dummyRxInterruptOnCompletion took the global lock. Then, a few lines later, it took the miniport lock.
At this point, the deadlock becomes entirely clear.