Crash Dump Analysis Patterns (Part 25c)

Sometimes threads related to file system operations may be blocked with not easily recognizable 3rd-party Top Module with only OS vendor modules such as NTFS or fltmgr present:

fltmgr! ?? ::FNODOBFM::`string’+0×2bfa


We see the same modules in I/O Request Stack Trace from the thread IRP. But because we see filter manager involved there may be some 3rd-party file system filters involved. Such filters are called before a device processes a request and also upon the completion of the request. There may be different filter callbacks registered for each case and they form a similar structure like I/O stack locations (we call this pattern Filter Stack Trace):

If one of such filters is blocked in a wait chain this may not be visible on I/O request or thread stacks because of possible asynchronous processing. But we may use !fltkd.irpctrl debugging extension command to examine the IRP context:

0: kd> !irp fffffa80162aa230
cmd flg cl Device File Completion-Context
[ 0, 0] 0 0 fffffa800cb28030 00000000 fffff880012048f0-fffffa8016f64010
\FileSystem\Ntfs fltmgr!FltpSynchronizedOperationCompletion
Args: 00000000 00000000 00000000 00000000
>[ 0, 0] 0 1 fffffa800ca00890 fffffa801060d070 00000000-00000000 pending
Args: fffff88014450868 02000060 00000006 00000000

0: kd> !fltkd.irpctrl fffffa8016f64010
Cmd IrpFl OpFl CmpFl Instance FileObjt Completion-Context Node Adr
--------- -------- ----- ----- -------- -------- ------------------ --------
[0,0] 00000884 00 0000 fffffa800d29c010 fffffa801060d070 fffff8800518b474-0000000000000000 fffffa8016f641e0
("luafv","luafv") luafv!LuafvPostCreate
Args: fffff88014450868 0000000002000060 0000000000000006 0000000000000000 0000000000000000 0000000000000000
>[0,0] 00000884 00 0000 fffffa800e8051d0 fffffa801060d070 fffff88006808440-0000000000000000 fffffa8016f64160
(”3rdPartyFilter”,”3rdPartyFilter Instance”) FilterA!FltDriver_PostOperationCallback
Args: fffff88014450868 0000000002000060 0000000000000006 0000000000000000 0000000000000000 0000000000000000


So we see that FilterA module may be involved in blocking the thread (Blocking Module pattern extended to I/O request and filter stack traces).

- Dmitry Vostokov @ + -

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