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

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

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.