Re: [Patch][RFC] Disabling per-tgid stats on task exit in taskstats

On Mon, 2006-03-07 at 18:01 -0700, Andrew Morton wrote:

On Mon, 03 Jul 2006 20:54:37 -0400
Shailabh Nagar [off-list ref] wrote:

quoted

quoted

What happens when a listener exits without doing deregistration
(or if the listener attempts to register another cpumask while a current
registration is still active).

( Jamal, your thoughts on this problem would be appreciated)

Problem is that we have a listener task which has "registered" with 
taskstats and caused
its pid to be stored in various per-cpu lists of listeners. Later, when 
some other task exits on a given cpu, its exit data is sent using 
genlmsg_unicast on each pid present on that cpu's list.

If the listener exits without doing a "deregister", its pid continues to 
be kept around, obviously not a good thing. So we need some way of 
detecting the situation (task is no longer listening on
these cpus events) that is efficient.

Also need to address the case where the listener has closed off his file
descriptor but continues to run.

So hooking into listener's exit() isn't appropriate - the teardown is
associated with the lifetime of the fd, not of the process.  If we do that,
exit() gets handled for free.  

If you are always going to send unicast messages, then  -ECONNREFUSED
will tell you the listener has closed their fd - this doesnt meant it
has exited. Besides that one process could open several sockets. I know
that would not be the app you would write - but it doesnt stop other
people from doing it.
I think i may not follow what you are doing - for some reason i thought
you may have many listeners in user space and these messages get
multicast to them?
Does the user space program somehow communicate its pid to the kernel?

cheers,
jamal