| Debugging Tools for Windows |
During a resource time out, the thread waiting for the resource will break into the kernel debugger with a message similar to the following:
ActiveCount = 0001 Flags = IsOwnedExclusive sharedWaiter
NumberOfExclusiveWaiters = 0000
Thread = 809cd2f0, Count = 01
Thread = 809ebc50, Count = 01
Thread = 00000000, Count = 00
Thread = 00000000, Count = 00
Thread = 00000000, Count = 00
NT!DbgBreakPoint+0x4:
800cee04: 000000ad callkd
The thread that holds the lock is the first thread listed (or multiple threads if it is a shared lock). To examine that thread, use a !thread extension on the thread ID (809cd2f0, in the previous example). This will give a stack for the thread owning the resource. If it is also waiting for a resource to become available, ExpWaitForResourceExclusive (or ExpWaitForResourceShared) will be on the stack for that thread.
The first parameter to ExpWaitForResourceXxx is the lock that is being waited on. To find out about that resource, use a !locks <resource id> extension, which will give you another thread to check.
If you get to a thread that is not waiting for another resource, that thread is probably the source of the problem. For a list of all held locks, use a !locks extension with no parameter at the kd> prompt.
ActiveCount = 0001 Flags = IsOwnedExclusive ExclusiveWaiter
NumberOfExclusiveWaiters = 0001
Thread = ffaf5410, Count = 01 // Here's the owning thread
Thread = 00000000, Count = 00
ntoskrnl!_DbgBreakPoint:
80131400 cc int 3
kd> kb // Start with a stack
ChildEBP RetAddr Args to Child
fcd44980 801154c0 fc664ee0 ffab45d0 00110001 ntoskrnl!_DbgBreakPoint
fcd4499c 80102521 fc664ee0 ffb08ea8 fcd44a4c ntoskrnl!_ExpWaitForResource+0x114 // Lock being waited on...
fcd449e8 fc6509fa e12597c8 fef27c08 fee4fca8 ntoskrnl!_ExAcquireResourceExclusiveLite+0xa5
00380020 00000000 00000000 00000000 00000000 nwrdr!_CreateScb+0x2ff
kd> !locks fc664ee0 // !locks resource address gives lock info
Resource @ nwrdr!_NwScavengerSpinLock (0xfc664ee0) Exclusively owned
Contention Count = 45
NumberOfExclusiveWaiters = 1
Threads: ffaf5410-01 // Owning thread again
1 total locks, 1 locks currently held
kd> !thread ffaf5410 // Check the owning thread
THREAD ffaf5410 Cid e7.e8 Teb: 7ffde000 WAIT: (Executive) KernelMode Non-Alertable
feecf698 SynchronizationEvent
IRP List:
fef29208: (0006,00b8) Flags: 00000884 Mdl: feed8328
Not impersonating
Owning Process ffaf5690
WaitTime (seconds) 2781250
Context Switch Count 183175
UserTime 0:00:23.0153
KernelTime 0:01:01.0187
Start Address 0x77f04644
Initial Sp fec6c000 Current Sp fec6b938
Priority 11 BasePriority 7 PriorityDecrement 0 DecrementCount 8
ChildEBP RetAddr Args to Child
fec6b950 801044fc feecf668 feecf668 00000080 ntoskrnl!KiSwapContext+0x25
fec6b974 fc655976 feecf698 00000000 00000000 ntoskrnl!_KeWaitForSingleObject+0x218
fec6ba5c fc6509fa e1263968 fef29208 feecf668 nwrdr!_ExchangeWithWait+0x38
fec6ba28 fc6533e5 feecf668 e125b3c8 ffafae08 nwrdr!_CreateScb+0x2ff
fec6bac0 fc652f26 feecf668 fec6bae4 fef29208 nwrdr!_CreateRemoteFile+0x2c9
fec6bb6c fc652b14 feecf668 fef29208 fee50b60 nwrdr!_NwCommonCreate+0x3a2
fec6bbac 80107aea fee50b60 fef29208 804052ac nwrdr!_NwFsdCreate+0x56
fec6bbc0 80142792 fef37700 fec6bdbc fee50b28 ntoskrnl!IofCallDriver+0x38
fec6bd10 80145403 fee50b60 00000000 fec6bdbc ntoskrnl!_IopParseDevice+0x6a0
fec6bd7c 80144c0c 00000000 fec6be34 00000040 ntoskrnl!_ObpLookupObjectName+0x479
fec6be5c 80127803 0012dd64 00000000 80127701 ntoskrnl!_ObOpenObjectByName+0xa2
fec6bef4 801385c3 0012dd64 0012dd3c 00000000 ntoskrnl!_NtQueryAttributesFile+0xc1
fec6bef4 77f716ab 0012dd64 0012dd3c 00000000 ntoskrnl!_KiSystemService+0x83
0012dd20 00000000 00000000 00000000 00000000 ntdll!_ZwQueryAttributesFile+0xb