cvs commit: src/sys/kern kern_event.c src/sys/sys eventvar.h

[Nate Lawson]

Doug Rabson wrote:
> On Wednesday 14 July 2004 19:56, Robert Watson wrote:
>>On Wed, 14 Jul 2004, Alfred Perlstein wrote:
>>>I can fix this by setting a "sigio in progress" on the kqeue and
>>>not calling pgsigio() while one is in progress.
>>
>>My worry is the inter-subsystem calling.  We often call KNOTE() while
>>holding existing locks in the calling subsystem that we can't drop.
>>Generally, kqueue is a leaf node subsystem in that it's called from
>>many places under many circumstances, and needs to not disrupt the
>>calling state by doing "weird things".  What's there before your
>>change is not too disruptive/weird; afterwards, we call into the body
>>of the process signalling code which requires additional process
>>locks.  Note that there are other paths to the same suffering: if any
>>other signal is delivered to a process that's monitoring for signals
>>with kqueue causing a sigio, you're still recursing into the signal
>>subsystem.
> 
> 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.

In fact, the AIO task threads already provide a convenient context for this.

-- 
-Nate