On 2025-06-10, Claudio Jeker wrote:
> On Tue, Jun 10, 2025 at 04:48:04AM -0400, Ted Unangst wrote:
> > Unless I've missed something, the only in use remnant of the hooks 
> > code is for startup hooks. And never disestablished.
> > 
> > So we can burn through one layer of abstraction, and also eliminate 
> > one unused function entirely.
> > 
> > There's also a collection of man.9 pages.
> 
> We have various hooks all over the place reimplementing the same code.
> Should we try to consolidate those instead. e.g. kthread_create_deferred
> is a prime example for reimplementing the wheel for no good reason.

This turns kthread_create_deferred into a startuphook. Independent of
previous diff. The functions appear to be used almost interchangably.
The only difference is that kthread will run immediately post boot,
while startuphook_establish called late will never run.

I think this is a first step, then delete the kthread interface and
add the "just run now" logic to startuphook_establish.

The only ordering consideration is in acpi. I think we should move the
thread creation there earlier, so it's running before any devices 
do stuff. (I think we should do this anyway, the acpi thread should be
running before child threads, no?)

Index: kern/init_main.c
===================================================================
RCS file: /home/cvs/src/sys/kern/init_main.c,v
diff -u -p -r1.329 init_main.c
--- kern/init_main.c	9 Jun 2025 10:57:46 -0000	1.329
+++ kern/init_main.c	10 Jun 2025 19:56:10 -0000
@@ -165,6 +165,7 @@ main(void *framep)
 	struct pdevinit *pdev;
 	extern struct pdevinit pdevinit[];
 	extern void disk_init(void);
+	extern int kthread_create_now;
 
 	/*
 	 * Initialize the current process pointer (curproc) before
@@ -429,10 +430,12 @@ main(void *framep)
 	}
 
 	/*
+	 * Run startup hooks.
 	 * Create any kernel threads whose creation was deferred because
 	 * initprocess had not yet been created.
 	 */
-	kthread_run_deferred_queue();
+	kthread_create_now = 1;
+	dostartuphooks();
 
 	/*
 	 * Now that device driver threads have been created, wait for
@@ -442,8 +445,6 @@ main(void *framep)
 	 */
 	while (config_pending)
 		tsleep_nsec(&config_pending, PWAIT, "cfpend", INFSLP);
-
-	dostartuphooks();
 
 #if NVSCSI > 0
 	config_rootfound("vscsi", NULL);
Index: kern/kern_kthread.c
===================================================================
RCS file: /home/cvs/src/sys/kern/kern_kthread.c,v
diff -u -p -r1.46 kern_kthread.c
--- kern/kern_kthread.c	26 Nov 2021 04:42:13 -0000	1.46
+++ kern/kern_kthread.c	10 Jun 2025 19:53:30 -0000
@@ -97,14 +97,6 @@ kthread_exit(int ecode)
 	/* NOTREACHED */
 }
 
-struct kthread_q {
-	SIMPLEQ_ENTRY(kthread_q) kq_q;
-	void (*kq_func)(void *);
-	void *kq_arg;
-};
-
-SIMPLEQ_HEAD(, kthread_q) kthread_q = SIMPLEQ_HEAD_INITIALIZER(kthread_q);
-
 /*
  * Defer the creation of a kernel thread.  Once the standard kernel threads
  * and processes have been created, this queue will be run to callback to
@@ -113,34 +105,9 @@ SIMPLEQ_HEAD(, kthread_q) kthread_q = SI
 void
 kthread_create_deferred(void (*func)(void *), void *arg)
 {
-	struct kthread_q *kq;
-
 	if (kthread_create_now) {
 		(*func)(arg);
 		return;
 	}
-
-	kq = malloc(sizeof *kq, M_TEMP, M_NOWAIT|M_ZERO);
-	if (kq == NULL)
-		panic("unable to allocate kthread_q");
-
-	kq->kq_func = func;
-	kq->kq_arg = arg;
-
-	SIMPLEQ_INSERT_TAIL(&kthread_q, kq, kq_q);
-}
-
-void
-kthread_run_deferred_queue(void)
-{
-	struct kthread_q *kq;
-
-	/* No longer need to defer kthread creation. */
-	kthread_create_now = 1;
-
-	while ((kq = SIMPLEQ_FIRST(&kthread_q)) != NULL) {
-		SIMPLEQ_REMOVE_HEAD(&kthread_q, kq_q);
-		(*kq->kq_func)(kq->kq_arg);
-		free(kq, M_TEMP, sizeof(*kq));
-	}
+	startuphook_establish(func, arg);
 }
Index: dev/acpi/acpi.c
===================================================================
RCS file: /home/cvs/src/sys/dev/acpi/acpi.c,v
diff -u -p -r1.448 acpi.c
--- dev/acpi/acpi.c	2 Jun 2025 02:20:56 -0000	1.448
+++ dev/acpi/acpi.c	10 Jun 2025 20:10:20 -0000
@@ -1031,6 +1031,8 @@ acpi_attach_common(struct acpi_softc *sc
 	    "acpiwqpl", NULL);
 	pool_setlowat(&acpiwqpool, 16);
 
+	kthread_create_deferred(acpi_create_thread, sc);
+
 	SIMPLEQ_INIT(&sc->sc_tables);
 	SIMPLEQ_INIT(&sc->sc_wakedevs);
 #if NACPIPWRRES > 0
@@ -1309,8 +1311,6 @@ acpi_attach_common(struct acpi_softc *sc
 	pci_dopm = 1;
 
 	acpi_attach_machdep(sc);
-
-	kthread_create_deferred(acpi_create_thread, sc);
 }
 
 int