In the windows kernel, at IRQLs you can use Spinlocks but not Mutexes.
The reason is Mutex structure holds ownership details meaning they only work with threads. At higher IRQLs >= DISPATCH_LEVEL, there's no concept of threads.
When we use KeWaitForSingleObject() on a thread, the scheduler switches this thread on sleep and runs another thread. The scheduler only handles threads not interrupts. That's why there should be no blocking at Higher IRQLs (Mutexes, accessing paged data etc)
Btw the Scheduler itself runs at DISPATCH_LEVEL. That's why thread level activity is only restricted to PASSIVE_LEVEL/APC_LEVEL
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