Using the System's Cancel Spin Lock

The system provides a single cancel spin lock, which is acquired or released when certain system routines are called.

Driver routines that change the state of cancelable IRPs, including all routines that might complete an IRP with STATUS_CANCELLED, must acquire and release the system cancel spin lock according to the guidelines in this section.

In drivers that use the I/O manager-supplied device queue, any driver routine other than the Cancel routine that changes the cancelable state of an IRP must first call IoAcquireCancelSpinLock to acquire the system cancel spin lock.

Acquiring the cancel spin lock ensures that only the caller can change the cancelable state of that IRP. While the caller holds the spin lock, the I/O manager cannot call the driver's Cancel routine for that IRP. Likewise, another driver routine, such as a DispatchCleanup routine, cannot simultaneously try to change the cancelable state of that IRP.

In drivers that manage their own queues of IRPs and use driver-supplied spin locks to synchronize queue access, the driver routines do not need to acquire the cancel spin lock before calling IoSetCancelRoutine. However, these drivers should check the Cancel routine pointer that IoSetCancelRoutine returns to determine whether the Cancel routine has already started. See Using a Driver-Supplied Spin Lock for details.

Any driver routine that calls IoAcquireCancelSpinLock must call IoReleaseCancelSpinLock as soon as possible.

A driver must never call IoCompleteRequest with an IRP while holding a spin lock. Attempting to complete an IRP while holding a spin lock can cause a deadlock.