Pool Tracking

Pool Tracking monitors the memory allocations made by the driver. At the time that the driver is unloaded, Driver Verifier ensures that all allocations made by the driver have been freed.

Unfreed memory allocations (also called memory leaks) are a common cause of lowered operating system performance. These can fragment the system pools and eventually cause system crashes.

When this option is active, Driver Verifier will issue bug check 0xC4 (with Parameter 1 equal to 0x62) if a driver unloads without freeing all its allocations.

If Driver Verifier issues this bug check with Parameter 1 equal to 0x51, 0x52, 0x53, 0x54, or 0x59, the driver has written to memory outside of its allocations. In this case, you should enable the Special Pool feature to locate the source of the error.

See Bug Check 0xC4 (DRIVER_VERIFIER_DETECTED_VIOLATION) for a list of the bug check parameters.

Starting with Windows Vista, enabling the Pool Tracking option also enables the tracking of locked pages. When this option is active, Driver Verifier will issue Bug Check 0xCB (DRIVER_LEFT_LOCKED_PAGES_IN_PROCESS) if a driver fails to release locked pages after an I/O operation.

In Windows 7 and later versions of the Windows operating system, the Pool Tracking option supports memory that was allocated by using the following kernel APIs:

In Windows 7 and later versions of the Windows operating system, when Pool Tracking is activated, Driver Verifier can detect attempts to allocate kernel pool memory with quota in the context of the Idle process. Such attempts usually mean that the driver is allocating memory from a DPC routine. The thread or process context for DPC routines is unreliable, so trying to charge quota to that process is incorrect.

Monitoring Pool Tracking

Memory pool allocation statistics can be monitored separately for each driver being verified. These statistics can be displayed by Driver Verifier Manager, the Verifier.exe command line, or in a log file. See Monitoring Individual Counters for details.

The kernel debugger extension !verifier 0x3 can be used to locate outstanding memory allocations after the driver is unloaded, or to track the current allocations while the driver is running. This extension also shows the pool tag, the size of the pool, and the address of the allocator for each allocation. For information about debugger extensions, see Windows Debugging.

Pool Quota Charges from DPC Routine

Kernel drivers can call ExAllocatePoolWithQuotaTag to allocate kernel pool memory and charge the number of bytes that are allocated to the pool quota of the current process. Drivers typically use quota for memory allocations that are directly related to a request that comes from an application.

Deferred procedure call (DPC) routines can run in the context of any process. Therefore, charging quota from a DPC routine charges a random process. Even worse, when the DPC routine runs in the context of the Idle process, this condition can result in memory corruption or system crashes.

Starting in Windows 7, Driver Verifier detects ExAllocatePoolWithQuotaTag calls from DPC routines.

Activating This Option

You can activate the Pool Tracking feature for one or more drivers by using Driver Verifier Manager or the Verifier.exe command line. For details, see Selecting Driver Verifier Options.

  • At the command line

    At the command line, the Pool Tracking option is represented by Bit 3 (0x8). To activate Pool Tracking, use a flag value of 0x8 or add 0x8 to the flag value. For example:

    
    verifier /flags 0x8 /driver MyDriver.sys
    
    

    The feature will be active after the next boot.

    On Windows Vista and later versions of Windows, you can also activate and deactivate Pool Tracking without rebooting the computer by adding the /volatile parameter to the command. For example:

    
    verifier /volatile /flags 0x8 /adddriver MyDriver.sys
    
    

    This setting is effective immediately, but is lost when you shut down or reboot the computer. For details, see Using Volatile Settings.

    The Pool Tracking feature is also included in the standard settings. For example:

    
    verifier /standard /driver MyDriver.sys
    
    
  • Using Driver Verifier Manager
    1. Start Driver Verifier Manager. Type Verifier in a Command Prompt window.
    2. Select Create custom settings (for code developers) and then click Next.
    3. Select Select individual settings from a full list.
    4. Select (check) Pool tracking.

    The Pool Tracking feature is also included in the standard settings. To use this feature, in Driver Verifier Manager, click Create Standard Settings.

 

 

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