Is it safe to lower IRP in completion routine?

NTDEV
1

I am getting bugcheck C4 when I try to call KeEnterCriticalRegion in IO
Completion routine. Reason being completion routine is called dispatch
level.
So wondering if I can lower the irql in completion routine and how to
achieve it.

Thanks,

–

Ruby

2

>

I am getting bugcheck C4 when I try to call KeEnterCriticalRegion in IO
Completion routine. Reason being completion routine is called dispatch level.
So wondering if I can lower the irql in completion routine and how to achieve
it.

I guess you’d schedule a workitem and return STATUS_MORE_PROCESSING_REQUIRED, then do your work in the workitem.

You can’t just lower the IRQL arbitrarily with KeLowerIrql, if that’s what you are asking.

James

3

Ruby Siddhu wrote:

I am getting bugcheck C4 when I try to call KeEnterCriticalRegion in
IO Completion routine. Reason being completion routine is called
dispatch level.
So wondering if I can lower the irql in completion routine and how to
achieve it.

It is NEVER safe to lower the IRQL, unless you are restoring to a level
that you raised from earlier.

You’re already at a raised IRQL. Are you sure you need a critical
region? If you have something you need to protect at various different
IRQLs, perhaps you should choose a different primitive.

–
Tim Roberts, xxxxx@probo.com
Providenza & Boekelheide, Inc.

4

> I am getting bugcheck C4 when I try to call KeEnterCriticalRegion in IO

Completion routine. Reason being completion routine is called dispatch
level.
So wondering if I can lower the irql in completion routine and how to
achieve it.

Thanks,

When you are in DISPATCH_LEVEL, you may not
(a) call any DDI function whose spec says < DISPATCH_LEVEL
(b) lower the IRQL

That’s what threads are for. You can use either a workitem with the
built-in thread queue or create a dedicated thread in your driver is a
design choice. Note that yoy must abandon the illusion that you can do
things sequentially; if, for example, your code is DL1(); PL1(); DL2(();
where DL is a function permitted at DISPATCH_LEVEL and PL Reqires
PASSIVE_LEVEL, you CANNOT write it as DL1(); QWI(); wait…; DL2();
because there is no way towait; instead, you must change your Queued Work
Item to be PL1(); DL2();.

You have to completely abandon the idea that textual sequentiality in the
source code must be used to represent sequentiality of execution.
joe

–

Ruby

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