Spinlock Use Guidelines

Here are some guidelines on using spinlocks to protect critical resources.

Define spinlocks only for critical resources. A read only I/O port is not a critical resource. A set of read only I/O ports that must all be read before a decision is made IS a critical resource. o

Do not define too many spinlocks. o

Use spinlocks for VERY SHORT durations only. As a general rule, calls should be avoided while owning a spinlock. o

Leave interrupts disabled after locking a spinlock. This prevents interrupts on the same processor and possible deadlock. o

Be careful to not make any calls that may try to lock a spinlock that is already locked. ADDs, when making asynchronous callbacks, can be reentered at their IORB entry point. o

Be aware that DevHelp_Block called with spinlocks locked will unlock them. When the block wakes up spinlocks must be reacquired. o

Never make a call that could block while owning a spinlock. For example, some DevHelp calls can block.

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