[src/trunk]: src/sys/dev/ic tpm(4): Fix disabling of rnd source if tpm is dea...

[riastradh <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/572a31a35b24
branches:  trunk
changeset: 1029075:572a31a35b24
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Mon Dec 20 23:05:55 2021 +0000

description:
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.

diffstat:

 sys/dev/ic/tpm.c    |  8 +++++---
 sys/dev/ic/tpmvar.h |  3 ++-
 2 files changed, 7 insertions(+), 4 deletions(-)

diffs (53 lines):

diff -r b5d323bd28da -r 572a31a35b24 sys/dev/ic/tpm.c
--- a/sys/dev/ic/tpm.c  Mon Dec 20 22:40:46 2021 +0000
+++ b/sys/dev/ic/tpm.c  Mon Dec 20 23:05:55 2021 +0000
@@ -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 @@
         */
        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 @@
 {
        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 -r b5d323bd28da -r 572a31a35b24 sys/dev/ic/tpmvar.h
--- a/sys/dev/ic/tpmvar.h       Mon Dec 20 22:40:46 2021 +0000
+++ b/sys/dev/ic/tpmvar.h       Mon Dec 20 23:05:55 2021 +0000
@@ -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 workqueue *sc_rndwq;
        struct work sc_rndwk;
        volatile unsigned sc_rndpending;
+       bool sc_rnddisabled;
 };
 
 bool tpm_suspend(device_t, const pmf_qual_t *);