> NMI interrupt handler cannot block so it trylocks against a spinlock
> instead. Buffer processing code needs to block against concurrent NMI
> interrupts so takes the spinlock for them. All actual blocks on the
> spinlock are beneath a down() on another semaphore, so a sleep whilst
> holding the spinlock won't actually cause deadlock.
If all accesses to the spinlock are taken under a semaphore, then the
spinlock is not needed (i.e. the down'ed semaphore provides the same
protection), or am I missing something?
If this is not the case - e.g. there are other accesses to these locks -
then you cannot sleep, no?
I really can think of no case in which it is safe to sleep while holding
a spinlock or otherwise atomic. If it is, then the atomicity is not
needed, sort of by definition.
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