[Sorry for the slow response time]
Garrett D'Amore wrote:
I'm not talking about consuming cycles. I'm not talking about wall
clock time considerations. I'm talking about potential deadlocks due to
cv_wait.
You must -not- under any conditions cv_wait while in ip_input's path.
Because you don't know anything about what locks or PIL the calling
context is coming from.
I don't think there is a hard and fast rule on this.
It is true that *typically* a mutex is used with a short or bounded hold
time, and that a condition variable might be used when the hold time is
unbounded.
But there might be subsystems that use a mutex (or rwlock) where the
hold time is unbounded.
And one can use condition variables to create mutual exclusion
primitives that have bounded hold time.
The 'interrupts as threads' support in the Solaris kernel can deal with
all combinations; a mutex_enter on an adaptive mutex will sleep if the
thread holding the mutex is not running.
Thus cv vs. mutex/rwlock is a red herring. What matters is whether the
hold time is bounded or not.
Erik
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