The default template argument is only used in one place, and it
looks like it was probably just an oversight. The rest of the Kernel
code all uses u8 as the type. So lets make that the default and remove
the unused template argument, as there doesn't seem to be a reason to
allow the size to be customizable.
This should help prevent deadlocks where a thread blocks on a Mutex
while interrupts are disabled, and makes it impossible for the holder of
the Mutex to make forward progress because it cannot be scheduled in.
Hide it behind a new debug macro LOCK_IN_CRITICAL_DEBUG for now, because
Ext2FS takes a series of Mutexes from the page fault handler, which
executes with interrupts disabled.
The LOCK_DEBUG conditional code is pretty ugly for a feature that we
only use rarely. We can remove a significant amount of this code by
utilizing a zero sized fake type when not building in LOCK_DEBUG mode.
This lets us keep the same API, but just let the compiler optimize it
away when don't actually care about the location the caller came from.
