Make the process_exit eventhandler run without Giant. Add Giant hooks

in the two consumers that need it.. processes using AIO and netncp.
Update docs.  Say that process_exec is called with Giant, but not to
depend on it.  All our consumers can handle it without Giant.

sys/kern/kern_exec.c

@@ -843,6 +843,7 @@ exec_new_vmspace(imgp, sv)
 
 	imgp->vmspace_destroyed = 1;
 
+	/* Called with Giant held, do not depend on it! */
 	EVENTHANDLER_INVOKE(process_exec, p);
 
 	/*

sys/kern/kern_exit.c

@@ -214,9 +214,7 @@ exit1(struct thread *td, int rv)
 	 * e.g. SYSV IPC stuff
 	 * XXX what if one of these generates an error?
 	 */
-	mtx_lock(&Giant);
 	EVENTHANDLER_INVOKE(process_exit, p);
-	mtx_unlock(&Giant);
 
 	MALLOC(p->p_ru, struct rusage *, sizeof(struct rusage),
 		M_ZOMBIE, M_WAITOK);

sys/kern/kern_fork.c

@@ -695,8 +695,6 @@ fork1(td, flags, pages, procp)
 	 * Both processes are set up, now check if any loadable modules want
 	 * to adjust anything.
 	 *   What if they have an error? XXX
-	 *
-	 * Handlers must be MPSAFE, or aquire Giant themselves if not.
 	 */
 	EVENTHANDLER_INVOKE(process_fork, p1, p2, flags);
 

sys/kern/vfs_aio.c

@@ -543,6 +543,7 @@ aio_proc_rundown(void *arg, struct proc *p)
 	if (ki == NULL)
 		return;
 
+	mtx_lock(&Giant);
 	ki->kaio_flags |= LIOJ_SIGNAL_POSTED;
 	while ((ki->kaio_active_count > 0) || (ki->kaio_buffer_count >
 	    ki->kaio_buffer_finished_count)) {
@@ -643,6 +644,7 @@ aio_proc_rundown(void *arg, struct proc *p)
 
 	uma_zfree(kaio_zone, ki);
 	p->p_aioinfo = NULL;
+	mtx_unlock(&Giant);
 }
 
 /*

sys/netncp/ncp_subr.c

@@ -85,6 +85,7 @@ ncp_at_exit(void *arg, struct proc *p)
 	struct ncp_conn *ncp, *nncp;
 	struct thread *td;
 
+	mtx_lock(&Giant);
 	FOREACH_THREAD_IN_PROC(p, td) {
 		if (ncp_conn_putprochandles(td) == 0)
 			continue;
@@ -100,6 +101,7 @@ ncp_at_exit(void *arg, struct proc *p)
 		}
 		ncp_conn_unlocklist(td);
 	}
+	mtx_unlock(&Giant);
 }
 
 int

sys/sys/eventhandler.h

@@ -158,8 +158,8 @@ EVENTHANDLER_DECLARE(vm_lowmem, vm_lowmem_handler_t);
 
 /*
  * Process events
- * process_fork handlers are called without Giant.
- * exit/exec handlers are called with Giant.
+ * process_fork and exit handlers are called without Giant.
+ * exec handlers are called with Giant, but that is by accident.
  */
 struct proc;