[src/trunk]: src/sys/dev/wscons The change from config_interrupts to a kthrea...

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

details:   https://anonhg.NetBSD.org/src/rev/7b5859398b5b
branches:  trunk
changeset: 949826:7b5859398b5b
user:      jmcneill <jmcneill%NetBSD.org@localhost>
date:      Sun Jan 17 16:51:12 2021 +0000

description:
The change from config_interrupts to a kthread for VCONS_DRAW_INTR init
unfortunately makes it easier to trigger a race that results in characters
not being erased properly at boot. Work around the original issue a
different way by creating a fake device_t and defer initialization until
we are sure that config_interrupt threads are done. This is not ideal and
the race is still present but fixing this properly would require a rewrite
to make this code MP-safe.

diffstat:

 sys/dev/wscons/wsdisplay_vcons.c |  30 ++++++++++++++++++------------
 1 files changed, 18 insertions(+), 12 deletions(-)

diffs (69 lines):

diff -r a34d56d1ece7 -r 7b5859398b5b sys/dev/wscons/wsdisplay_vcons.c
--- a/sys/dev/wscons/wsdisplay_vcons.c  Sun Jan 17 16:32:36 2021 +0000
+++ b/sys/dev/wscons/wsdisplay_vcons.c  Sun Jan 17 16:51:12 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: wsdisplay_vcons.c,v 1.45 2021/01/02 03:00:56 macallan Exp $ */
+/*     $NetBSD: wsdisplay_vcons.c,v 1.46 2021/01/17 16:51:12 jmcneill Exp $ */
 
 /*-
  * Copyright (c) 2005, 2006 Michael Lorenz
@@ -27,7 +27,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: wsdisplay_vcons.c,v 1.45 2021/01/02 03:00:56 macallan Exp $");
+__KERNEL_RCSID(0, "$NetBSD: wsdisplay_vcons.c,v 1.46 2021/01/17 16:51:12 jmcneill Exp $");
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -121,7 +121,7 @@
 #ifdef VCONS_DRAW_INTR
 static void vcons_intr(void *);
 static void vcons_softintr(void *);
-static void vcons_init_thread(void *);
+static int vcons_intr_enable(device_t);
 #endif
 
 int
@@ -180,11 +180,16 @@
        callout_setfunc(&vd->intr, vcons_intr, vd);
        vd->intr_valid = 1;
 
-       if (kthread_create(PRI_NONE, 0, NULL, vcons_init_thread, vd, NULL,
-           "vcons_init") != 0) {
-               printf("%s: unable to create thread.\n", __func__);
-               return -1;
-       }
+       /*
+        * Defer intr drawing until after autoconfiguration has completed
+        * to serialize device attachment messages w/ the initial screen
+        * redraw as a workaround for the lack of MP-safeness in this
+        * subsystem. To register with autoconf, we need to create a fake
+        * device_t and pass that in as a handle to config_interrupts.
+        */
+       snprintf(vd->fake_dev.dv_xname, sizeof(vd->fake_dev.dv_xname), "vcons");
+       vd->fake_dev.dv_private = vd;
+       config_finalize_register(&vd->fake_dev, vcons_intr_enable);
 #endif
        return 0;
 }
@@ -1493,14 +1498,15 @@
        callout_schedule(&vd->intr, mstohz(33));
 }
 
-static void
-vcons_init_thread(void *cookie)
+static int
+vcons_intr_enable(device_t fake_dev)
 {
-       struct vcons_data *vd = (struct vcons_data *)cookie;
+       struct vcons_data *vd = device_private(fake_dev);
 
        vd->use_intr = 2;
        callout_schedule(&vd->intr, mstohz(33));
-       kthread_exit(0);
+
+       return 0;
 }
 #endif /* VCONS_DRAW_INTR */