First thread in proc in not passed to thread_dtor eventhandler upon exit

[Konstantin Belousov]

On Sun, Feb 19, 2017 at 09:43:24AM +0100, Hans Petter Selasky wrote:
> On 02/19/17 04:54, Konstantin Belousov wrote:
> > On Sat, Feb 18, 2017 at 10:40:00PM +0100, Hans Petter Selasky wrote:
> >> Hi,
> >>
> >> Is the following a bug or feature. I observe that the first thread in a
> >> procedure is not passed to thread_dtor as declared by the following
> >> eventhandler, when the procedure exits.
> >>
> >> EVENTHANDLER_DECLARE(thread_dtor, thread_dtor_fn);
> >>
> >> Is this a bug or feature?
> > This is a feature.  When a zombie process is reaped, the last thread in
> > the process (the one which exited it) is left in the process thread list.
> > This is an optimization, because process without at least one thread
> > is never useful.
> >
> > You can see the code in fork1() which allocates struct proc from zone
> > and then checks if there any thread pre-allocated as well (both struct
> > proc and struct thread are type-stable).
> >
> > Since the last thread is not freed, its destructor is not signalled.
> 
> Hi Konstantin,
> 
> I see. To avoid leakage of LinuxKPI, Linux and Dtrace resources to all 
> system threads, I think the attached patch is required. What do you 
> think about the attached patch? If you don't like it can you suggest 
> another approach?
Your patch is in-line with e.g. osd handling, so I do not see a reason
to suggest a different approach.  Looks fine.

Of course, the only worry is the fact that event handlers are called
for the thread which is not newly allocated nor just freed.

> diff --git a/sys/kern/kern_proc.c b/sys/kern/kern_proc.c
> index f39326f..a206a0a 100644
> --- a/sys/kern/kern_proc.c
> +++ b/sys/kern/kern_proc.c
> @@ -191,11 +191,17 @@ static int
>  proc_ctor(void *mem, int size, void *arg, int flags)
>  {
>  	struct proc *p;
> +	struct thread *td;
>  
>  	p = (struct proc *)mem;
>  	SDT_PROBE4(proc, , ctor , entry, p, size, arg, flags);
>  	EVENTHANDLER_INVOKE(process_ctor, p);
>  	SDT_PROBE4(proc, , ctor , return, p, size, arg, flags);
> +	td = FIRST_THREAD_IN_PROC(p);
> +	if (td != NULL) {
> +		/* Make sure all thread constructors are executed */
> +		EVENTHANDLER_INVOKE(thread_ctor, td);
> +	}
>  	return (0);
>  }
>  
> @@ -220,6 +226,9 @@ proc_dtor(void *mem, int size, void *arg)
>  #endif
>  		/* Free all OSD associated to this thread. */
>  		osd_thread_exit(td);
> +
> +		/* Make sure all thread destructors are executed */
> +		EVENTHANDLER_INVOKE(thread_dtor, td);
>  	}
>  	EVENTHANDLER_INVOKE(process_dtor, p);
>  	if (p->p_ksi != NULL)