From 344cf1cc8436066569b4fdc2056aeaf32c0af903 Mon Sep 17 00:00:00 2001
From: riastradh <riastradh@NetBSD.org>
Date: Mon, 20 Dec 2021 23:05:55 +0000
Subject: [PATCH] tpm(4): Fix disabling of rnd source if tpm is deactivated.

Nothing prevents a second worker from being queued when the first one
is about to do rnd_detach_source.  Instead, just set a flag so future
requests don't bother running a new thread; if there's a concurrent
one that's already been scheduled on another CPU, well, too bad, we
get a couple extra log messages but that's fine.

A better way to do this would probably be to detect whether the tpm
is deactivated at attach time, but that requires reading more of the
tpm spec than I care to do when there are alternative ways to
procrastinate like scrubbing the toilet.
---
 sys/dev/ic/tpm.c    | 8 +++++---
 sys/dev/ic/tpmvar.h | 3 ++-
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/sys/dev/ic/tpm.c b/sys/dev/ic/tpm.c
index 98868fc4ce99..7cb574d23fa3 100644
--- a/sys/dev/ic/tpm.c
+++ b/sys/dev/ic/tpm.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: tpm.c,v 1.22 2021/06/02 21:35:17 riastradh Exp $	*/
+/*	$NetBSD: tpm.c,v 1.23 2021/12/20 23:05:55 riastradh Exp $	*/
 
 /*
  * Copyright (c) 2019 The NetBSD Foundation, Inc.
@@ -48,7 +48,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: tpm.c,v 1.22 2021/06/02 21:35:17 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: tpm.c,v 1.23 2021/12/20 23:05:55 riastradh Exp $");
 
 #include <sys/param.h>
 #include <sys/types.h>
@@ -650,7 +650,7 @@ tpm_rng_work(struct work *wk, void *cookie)
 	 */
 	if (rv) {
 		device_printf(sc->sc_dev, "deactivating entropy source\n");
-		rnd_detach_source(&sc->sc_rnd);
+		atomic_store_relaxed(&sc->sc_rnddisabled, true);
 		/* XXX worker thread can't workqueue_destroy its own queue */
 	}
 
@@ -666,6 +666,8 @@ tpm_rng_get(size_t nbytes, void *cookie)
 {
 	struct tpm_softc *sc = cookie;
 
+	if (atomic_load_relaxed(&sc->sc_rnddisabled))
+		return;		/* tough */
 	if (atomic_swap_uint(&sc->sc_rndpending, MIN(nbytes, UINT_MAX/NBBY))
 	    == 0)
 		workqueue_enqueue(sc->sc_rndwq, &sc->sc_rndwk, NULL);
diff --git a/sys/dev/ic/tpmvar.h b/sys/dev/ic/tpmvar.h
index 9a4c1aae421c..1b08d5429d8b 100644
--- a/sys/dev/ic/tpmvar.h
+++ b/sys/dev/ic/tpmvar.h
@@ -1,4 +1,4 @@
-/*	$NetBSD: tpmvar.h,v 1.9 2021/01/04 18:26:59 riastradh Exp $	*/
+/*	$NetBSD: tpmvar.h,v 1.10 2021/12/20 23:05:55 riastradh Exp $	*/
 
 /*
  * Copyright (c) 2019 The NetBSD Foundation, Inc.
@@ -98,6 +98,7 @@ struct tpm_softc {
 	struct workqueue *sc_rndwq;
 	struct work sc_rndwk;
 	volatile unsigned sc_rndpending;
+	bool sc_rnddisabled;
 };
 
 bool tpm_suspend(device_t, const pmf_qual_t *);