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Date: Wed, 14 Jul 2004 22:50:29 -0700 (PDT)
From: Don Lewis <truckman@FreeBSD.org>
To: alfred@FreeBSD.org
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Subject: Re: cvs commit: src/sys/kern kern_event.c src/sys/sys eventvar.h
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On 14 Jul, Alfred Perlstein wrote:
> * Don Lewis <truckman@FreeBSD.org> [040714 13:38] wrote:
>> On 14 Jul, Alfred Perlstein wrote:
>> > * Doug Rabson <dfr@nlsystems.com> [040714 12:01] wrote:
>> 
>> >> Seems to me that the best thing to do is to defer the psigio() to a 
>> >> taskqueue that will run in a simpler locking environment.
>> > 
>> > I was thinking that, but I'm worried about "stale delivery",
>> > perhaps we need to record the generation count (process start time)
>> > in the sigio as well as the request sent, so that we don't send
>> > a signal to the wrong process.
>> 
>> This is already handled in the sigio infrastructure.  Both struct proc
>> and struct pgrp have a list of their potential sigio sources. When the
>> process or process group goes away, the exit code disables sigio
>> delivery.
> 
> Yes, but if the delivery of the signal becomes async, then we lose
> this.

Push a reference to the struct sigio onto the taskqueue would be a quick
and dirty way of dealing with this.  The ugly part is that it would mean
adding a reference count and a valid flag to the struct sigio.