Properties of Spinlocks

It is important to note the differences in the various types of spinlocks.

Properties of kernel spinlocks:

o

can have nested ownership.

can use a level to enforce a lock hierarchy.

can not be owned while outside of the kernel.

can only be owned for very short periods of time.

can not block while owning a spinlock.

Properties of device driver spinlocks:

o

can't have nested ownership.

can't use a level to enforce a lock hierarchy.

can be held outside of the kernel.

can only be owned for very short periods of time.

There is a different type of spinlock which is exported to subsystems. These locks are used to provide an efficient MP safe CLI/STI substitute for protecting data structures that are shared between task-time and interrupt-time code.

Properties of subsystem spinlocks:

o

can't have nested ownership.

can't use a level to enforce a lock hierarchy.

can be held outside of the kernel.

can only be used for very short periods of time.

each processor can hold only one subsystem spinlock at a time.

A suspend lock, is defined such that an attempt to acquire a suspend lock which is currently owned by another processor places the current thread into a blocked state, and causes a reschedule. The thread's which are blocked on suspend locks will awaken when the lock is released. Suspend locks are only used inside the kernel.

Properties of a kernel suspend lock:

o

can have nested ownership.

can use a level to enforce a lock hierarchy.

can not be owned while outside of the kernel.

can be owned for long periods of time.

can not block while owning a suspend lock.

When a spinlock is acquired, the lock manager automatically saves the state of the interrupt flag, then disables interrupts before returning to the caller. It restores the state of the interrupt flag when the lock is released. The kernel will panic if an interrupt is taken while owning a spinlock.