How to prevent context switching?

Hi,

I am bit new to driver programming. I would like to know how to prevent
context switching between threads.

Here is the scenario:

Thread A is running at PASSIVE LEVEL, driver gets into some funny state and
hence I want to panic the system so that I can get a memory dump to diaognise
the problem. So before crashing, I copy required data in a temporary buffer.
When I am about to panic the system, another thread B gets scheduled,
pre-empts the already running thread A, does context switching and runs for a
short burst and clear the data from my main buffer. Once thread B finshes,
thread A resumes the operation and panics the system. When I analyze memory
dump, I notice that contents in temp buffer and main buffer differ because of
context switching.

I want to know how do I prevent this context switching between threads A and
B? As soon as I get into funny state, I want to copy the data in temporary
buffer and crash the system.

Thanks.

Steve
Mon Apr 25 23:10:59 CDT 2005

Simple, use a dispatcher object to sync access to the
data. See help for KeInitializeEvent() and
SynchronizationEvent.

If either thread can run at DISPATCH_LEVEL, then use a
spinlock instead.

Steve.

>-----Original Message-----
>Hi,
>
>I am bit new to driver programming. I would like to know
how to prevent
>context switching between threads.
>
>Here is the scenario:
>
>Thread A is running at PASSIVE LEVEL, driver gets into
some funny state and
>hence I want to panic the system so that I can get a
memory dump to diaognise
>the problem. So before crashing, I copy required data in
a temporary buffer.
>When I am about to panic the system, another thread B
gets scheduled,
>pre-empts the already running thread A, does context
switching and runs for a
>short burst and clear the data from my main buffer. Once
thread B finshes,
>thread A resumes the operation and panics the system.
When I analyze memory
>dump, I notice that contents in temp buffer and main
buffer differ because of
>context switching.
>
>I want to know how do I prevent this context switching
between threads A and
>B? As soon as I get into funny state, I want to copy the
data in temporary
>buffer and crash the system.
>
>Thanks.
>.
>

Gary
Mon Apr 25 23:20:32 CDT 2005

Use a Spin lock to raise to DISPATCH_LEVEL, save your data, then lower to
PASSIVE. But I would simply panic, crash and then analyze the dump. I know
enough to copy the data, I therefore should know enough to find the data in
a dump.

--
Gary G. Little

"Nikhil" <Nikhil@discussions.microsoft.com> wrote in message
news:01D6DE60-FBBB-4D1D-B915-C2919E68EB6B@microsoft.com...
> Hi,
>
> I am bit new to driver programming. I would like to know how to prevent
> context switching between threads.
>
> Here is the scenario:
>
> Thread A is running at PASSIVE LEVEL, driver gets into some funny state
> and
> hence I want to panic the system so that I can get a memory dump to
> diaognise
> the problem. So before crashing, I copy required data in a temporary
> buffer.
> When I am about to panic the system, another thread B gets scheduled,
> pre-empts the already running thread A, does context switching and runs
> for a
> short burst and clear the data from my main buffer. Once thread B finshes,
> thread A resumes the operation and panics the system. When I analyze
> memory
> dump, I notice that contents in temp buffer and main buffer differ because
> of
> context switching.
>
> I want to know how do I prevent this context switching between threads A
> and
> B? As soon as I get into funny state, I want to copy the data in temporary
> buffer and crash the system.
>
> Thanks.

Nikhil
Tue Apr 26 16:34:02 CDT 2005

Thank you. I raised IRQL level to DISPATCH_LEVEL to solve the problem.

"Gary G. Little" wrote:

> Use a Spin lock to raise to DISPATCH_LEVEL, save your data, then lower to
> PASSIVE. But I would simply panic, crash and then analyze the dump. I know
> enough to copy the data, I therefore should know enough to find the data in
> a dump.
>
> --
> Gary G. Little
>
> "Nikhil" <Nikhil@discussions.microsoft.com> wrote in message
> news:01D6DE60-FBBB-4D1D-B915-C2919E68EB6B@microsoft.com...
> > Hi,
> >
> > I am bit new to driver programming. I would like to know how to prevent
> > context switching between threads.
> >
> > Here is the scenario:
> >
> > Thread A is running at PASSIVE LEVEL, driver gets into some funny state
> > and
> > hence I want to panic the system so that I can get a memory dump to
> > diaognise
> > the problem. So before crashing, I copy required data in a temporary
> > buffer.
> > When I am about to panic the system, another thread B gets scheduled,
> > pre-empts the already running thread A, does context switching and runs
> > for a
> > short burst and clear the data from my main buffer. Once thread B finshes,
> > thread A resumes the operation and panics the system. When I analyze
> > memory
> > dump, I notice that contents in temp buffer and main buffer differ because
> > of
> > context switching.
> >
> > I want to know how do I prevent this context switching between threads A
> > and
> > B? As soon as I get into funny state, I want to copy the data in temporary
> > buffer and crash the system.
> >
> > Thanks.
>
>
>

David
Tue Apr 26 17:39:32 CDT 2005

You realize this is just a 'quick fix' and will never work in production?
Thread 'B' can run on SMP systems. This includes the HT and dual core CPUs
as well as the Xenon, MP, and Opteron systems. Access to the buffer must be
controlled. If 'A' needs the buffer it must have a way to stop 'B' from
touching the buffer. The reverse is also true. We no longer write code for
the 8088 running DOS, except for BIOS and embedded folks.

"Nikhil" <Nikhil@discussions.microsoft.com> wrote in message
news:379256C1-AF66-4381-9171-341C02F5791A@microsoft.com...
> Thank you. I raised IRQL level to DISPATCH_LEVEL to solve the problem.
>
> "Gary G. Little" wrote:
>
>> Use a Spin lock to raise to DISPATCH_LEVEL, save your data, then lower to
>> PASSIVE. But I would simply panic, crash and then analyze the dump. I
>> know
>> enough to copy the data, I therefore should know enough to find the data
>> in
>> a dump.
>>
>> --
>> Gary G. Little
>>
>> "Nikhil" <Nikhil@discussions.microsoft.com> wrote in message
>> news:01D6DE60-FBBB-4D1D-B915-C2919E68EB6B@microsoft.com...
>> > Hi,
>> >
>> > I am bit new to driver programming. I would like to know how to prevent
>> > context switching between threads.
>> >
>> > Here is the scenario:
>> >
>> > Thread A is running at PASSIVE LEVEL, driver gets into some funny state
>> > and
>> > hence I want to panic the system so that I can get a memory dump to
>> > diaognise
>> > the problem. So before crashing, I copy required data in a temporary
>> > buffer.
>> > When I am about to panic the system, another thread B gets scheduled,
>> > pre-empts the already running thread A, does context switching and runs
>> > for a
>> > short burst and clear the data from my main buffer. Once thread B
>> > finshes,
>> > thread A resumes the operation and panics the system. When I analyze
>> > memory
>> > dump, I notice that contents in temp buffer and main buffer differ
>> > because
>> > of
>> > context switching.
>> >
>> > I want to know how do I prevent this context switching between threads
>> > A
>> > and
>> > B? As soon as I get into funny state, I want to copy the data in
>> > temporary
>> > buffer and crash the system.
>> >
>> > Thanks.
>>
>>
>>