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Date: Sun, 20 Feb 2005 08:08:11 -0700
From: Scott <scottl@samsco.org>
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To: "Daniel O'Connor" <doconnor@gsoft.com.au>
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cc: freebsd-hackers@freebsd.org
cc: Peter Jeremy <PeterJeremy@optushome.com.au>
Subject: Re: Signalling a process from a INTR_FAST handler
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Daniel O'Connor wrote:
> On Sun, 20 Feb 2005 16:12, Peter Jeremy wrote:
> 
>>I have a hardware interrupt handler that has to forward a signal to
>>userland and that I'd like to mark INTR_FAST.  AFAIK, the normal way
>>to forward a signal is:
>>	if ((p = pfind(sc->pid_to_signal)) != NULL) {
>>		psignal(p, SIGUSR2);
>>		PROC_UNLOCK(p);
>>	}
>>
>>But pfind(9) does a PROC_LOCK() which implies it can sleep and therefore
>>can't be used by an INTR_FAST handler.
>>
>>Firstly, am I correct?  If so, is there an alternative approach I can use?
> 
> 
> I think you are, and I think the only way to do it is to schedule another 
> kernel [heavy] thread to do the wakeup.
> 

You can shift the operation off to a fast taskqueue.  This assumes that
latency between the interrupt and the signal delivery is not critical.

Scott