Re: [PATCH] stap/staprun do not terminate properly

[Josh Stone <jistone at redhat dot com>]

On 03/07/2014 01:09 PM, David Smith wrote:
> So, instead I did this:
> 
> ====
> stap_stap_task_finder()
> {
>   // ...
> 
>   __stp_tf_cancel_task_work();
> 
>   // Note that utrace_exit() calls stp_task_work_exit()
>   utrace_exit();
> }
> ====
> 
> This moves canceling all outstanding task_work items before shutting
> down utrace (and calling stp_task_work_exit()). I think the end result
> is the same as your patch, and I think this makes a little more sense.
> This way we've canceled all the task_work items before shutting down
> utrace (and freeing all the memory allocated for utrace).
> 
> If this doesn't work for you or you see a hole in this logic please let
> me know.

I notice that utrace_exit() calls utrace_shutdown(), but so does
__stp_task_finder_cleanup() earlier in stap_stop_task_finder().  So in
fact the shutdown is still happening before canceling this work, and the
only thing left for utrace_exit() is the kmem_cache_destroy and
stp_task_work_exit().  Do you think this could be a problem?

In particular, I worry about this comment:

  /* After calling tracepoint_synchronize_unregister(), we're
   * sure there are no outstanding tracepoint probes being
   * called.  So, now would be a great time to free everything. */

There won't be any outstanding tracepoint handlers, but couldn't there
still be outstanding task_work scheduled from those handlers?