xenserver/win-xenvbd — pull request #1 by OwenSmith (2013-06-24 10:55:45+00:00)
Title: Prevent C4 BSOD when Verifier is active (deadlock detection)

When the suspend callback is triggered, a spinlock is held by the bus driver. Attempts to acquire a spinlock during the state changes can cause verifier to detect a potential deadlock. Remove the frontend state spinlock during the suspend callback frontend state changes, its called as DISPATCH on 1 vCPU with interrupts enabled so shouldnt attempt to acquire the state spinlock.