What does Windows error code 207 (ERROR_RING2_STACK_IN_USE) mean?

ERROR_RING2_STACK_IN_USE

What ERROR_RING2_STACK_IN_USE means

ERROR_RING2_STACK_IN_USE is Win32 system error code associated with the documented message: “The ring 2 stack is in use.” The significant condition is that a protected-mode compatibility operation cannot proceed because the ring-2 stack is already active.

Likely causes

• nested entry into a legacy ring-2 service occurs before the first call unwinds
• a fault or callback leaves compatibility-layer stack state marked busy
• unsupported reentrancy in an old driver or subsystem component

Troubleshooting steps

1. Capture the call sequence leading to the second ring-2 entry
2. look for callbacks, exceptions, or long jumps that bypass normal stack cleanup
3. serialize the legacy operation or move it to the environment for which it was designed

Code-specific investigation notes

Ring transitions use dedicated stack state so that privileged compatibility code does not continue on an unsuitable caller stack. Reentry while that state is active is rejected.

Correlate the failure with callbacks, signal handlers, and exception paths that can invoke the same service recursively.

A serialization workaround should be tested under failure injection to ensure every exit path clears the busy state.

Difference from related errors

ERROR_NESTING_NOT_ALLOWED is a general nesting restriction; it identifies the protected-mode stack resource that prevents reentry.

References

• Microsoft: System error codes 0–499