Re: [patch] Minor PAGG attach/detach semantic change for 2.6.11

On Thu, Sep 29, 2005 at 10:12:06AM -0500, Erik Jacobson wrote:
> > __pnotify_exit() would need to call the exit callback for all clients
> > except for the client failing the fork call.  To do this wouldn't the
> > following be needed in __pnotify_fork()?
> 
> If the fork fails in copy_process, we go to cleanup in copy_process, 
> not exit.c.  So, with the revision, if the the pnotify kernel module
> subscriber returns a failure for the process, that failure is passed 
> along to the copy_process call.  There, we go to bad_fork_cleanup_namespace
> where a pnotify_exit is done on the process that failed to fork.
> 
> In the old version, the pnotify_exit would have also been run within
> __pnotify_fork.  In the new version, we don't run the pnotify_exit
> from __pnotify_fork because we know it will be run in the fork failure
> path of copy_process.  That should mean that pnotify_exit will only
> execute once.  I think that means that your suggestion for adding 
> a pnotify_unsubscribe isn't necessary?  The unsubscribe is done by
> __pnotify_exit in this case.  Or am I still missing the point here?
> Sorry if it isn't getting through my head.

That's okay.  I've taken a look at the test version and it doesn't
seem like its doing what I suggested, so let me try again.

My suggestion is that the unsubscribe exit callback should only be
done for clients who successfully subscribed. For example, during a
fork:

1. Client A subscribes with its subscriber->events->fork() being
successful.
   
2. Client B subscribes with its subscriber->events->fork() being
successful.

3. Client C fails the fork and its subscriber->events->fork() returns
a failure.  Client C has its subscription removed from the pnotify
list but its subscriber->events->exit() callback should not be called.

4. Client A & B are unsubscribed and their subscriber->events->exit()
callbacks are invoked. 


Right now, AFAICS, client C would have its subscriber->events->exit()
callback invoked in spite of a failure.  IMHO the exit() callback
should only ever be called for a client for whom its fork() callback
succeeded.  What do you think?

> 
> See the RCU test version of pnotify in the download site under
> pnotify-test.  My attempts at posting that patch to the list seem to be
> eaten by the list server right now.  When that's fixed, I'll start posting
> stuff here.
> 
> Erik

Thanks,
-- 
		Kingsley