spinlocks and preemption

[Bahadir Balban <bilgehan.balban@xxxxxxxxx>]

Hi,

I have some basic questions. Answering just yes or no should suffice
for me. If we say there are 3 levels of execution context:

1) Process context
2) Bottom-Half context
3) Irq context

Is it correct to say that;

1) An in-interrupt context cannot sleep but it can be preempted if the
irqs are enabled. (Examples: inside a non-SA_INTERRUPT interrupt
handler or a tasklet)

Spinlocks:
2) No matter what context you are in, by acquiring a spinlock,
preemption is *always* disabled, to cover for the *always possible*
case of another process scheduling and deadlocking on the lock.

3) No matter what context you're in, *if, and only if* your spinlock
is shared with BH and/or Irq contexts, you disable them on the current
CPU, for they may interrupt yours, and deadlock on your spinlock.

4) Disabling of contexts for a spinlock is to protect against
deadlocks from the current CPU, whereas the spinlock itself is to
protect against races across CPUs. Does this also imply, the runqueue
of a CPU would never be balanced when a context on that CPU holds a
spinlock?

Thanks,
Bahadir

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