Add a enter_ddb() "accessop" to wsdisplay(4) to allow KMS drivers to bypass

the modeset lock when entering ddb.  This avoids triggering various asserts
when the kernel panics while running X.

ok deraadt@

5 files changed, 48 insertions, 6 deletions

diff --git a/sys/arch/amd64/amd64/db_interface.c b/sys/arch/amd64/amd64/db_interface.c
index c68c74026d9..a8931294d51 100644
--- a/sys/arch/amd64/amd64/db_interface.c
+++ b/sys/arch/amd64/amd64/db_interface.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: db_interface.c,v 1.28 2017/04/30 16:45:45 mpi Exp $	*/
+/*	$OpenBSD: db_interface.c,v 1.29 2017/07/19 14:34:10 kettenis Exp $	*/
 /*	$NetBSD: db_interface.c,v 1.1 2003/04/26 18:39:27 fvdl Exp $	*/
 
 /*
@@ -112,7 +112,7 @@ db_ktrap(int type, int code, db_regs_t *regs)
 	int s;
 
 #if NWSDISPLAY > 0
-	wsdisplay_switchtoconsole();
+	wsdisplay_enter_ddb();
 #endif
 
 	switch (type) {
diff --git a/sys/arch/i386/i386/db_interface.c b/sys/arch/i386/i386/db_interface.c
index 07d123ba1c2..db211b13175 100644
--- a/sys/arch/i386/i386/db_interface.c
+++ b/sys/arch/i386/i386/db_interface.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: db_interface.c,v 1.35 2017/04/30 16:45:45 mpi Exp $	*/
+/*	$OpenBSD: db_interface.c,v 1.36 2017/07/19 14:34:10 kettenis Exp $	*/
 /*	$NetBSD: db_interface.c,v 1.22 1996/05/03 19:42:00 christos Exp $	*/
 
 /*
@@ -106,7 +106,7 @@ db_ktrap(int type, int code, db_regs_t *regs)
 	int s;
 
 #if NWSDISPLAY > 0
-	wsdisplay_switchtoconsole();
+	wsdisplay_enter_ddb();
 #endif
 
 	switch (type) {
diff --git a/sys/dev/pci/drm/i915/i915_drv.c b/sys/dev/pci/drm/i915/i915_drv.c
index 327b17e7737..cb6a43c6b6e 100644
--- a/sys/dev/pci/drm/i915/i915_drv.c
+++ b/sys/dev/pci/drm/i915/i915_drv.c
@@ -1879,6 +1879,7 @@ void	inteldrm_free_screen(void *, void *);
 int	inteldrm_show_screen(void *, void *, int,
 	    void (*)(void *, int, int), void *);
 void	inteldrm_doswitch(void *);
+void	inteldrm_enter_ddb(void *, void *);
 int	inteldrm_load_font(void *, void *, struct wsdisplay_font *);
 int	inteldrm_list_font(void *, struct wsdisplay_font *);
 int	inteldrm_getchar(void *, int, int, struct wsdisplay_charcell *);
@@ -1908,6 +1909,7 @@ struct wsdisplay_accessops inteldrm_accessops = {
 	.alloc_screen = inteldrm_alloc_screen,
 	.free_screen = inteldrm_free_screen,
 	.show_screen = inteldrm_show_screen,
+	.enter_ddb = inteldrm_enter_ddb,
 	.getchar = inteldrm_getchar,
 	.load_font = inteldrm_load_font,
 	.list_font = inteldrm_list_font,
@@ -2033,6 +2035,20 @@ inteldrm_doswitch(void *v)
 		(*dev_priv->switchcb)(dev_priv->switchcbarg, 0, 0);
 }
 
+void
+inteldrm_enter_ddb(void *v, void *cookie)
+{
+	struct inteldrm_softc *dev_priv = v;
+	struct rasops_info *ri = &dev_priv->ro;
+	struct drm_fb_helper *helper = &dev_priv->fbdev->helper;
+
+	if (cookie == ri->ri_active)
+		return;
+
+	rasops_show_screen(ri, cookie, 0, NULL, NULL);
+	drm_fb_helper_debug_enter(helper->fbdev);
+}
+
 int
 inteldrm_getchar(void *v, int row, int col, struct wsdisplay_charcell *cell)
 {
diff --git a/sys/dev/wscons/wsdisplay.c b/sys/dev/wscons/wsdisplay.c
index 90c8f4680e1..74102fa0962 100644
--- a/sys/dev/wscons/wsdisplay.c
+++ b/sys/dev/wscons/wsdisplay.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: wsdisplay.c,v 1.127 2017/07/18 21:27:50 kettenis Exp $ */
+/* $OpenBSD: wsdisplay.c,v 1.128 2017/07/19 14:34:10 kettenis Exp $ */
 /* $NetBSD: wsdisplay.c,v 1.82 2005/02/27 00:27:52 perry Exp $ */
 
 /*
@@ -2137,6 +2137,30 @@ wsdisplay_switchtoconsole(void)
 }
 
 /*
+ * Switch rhe console display to its ddb screen, avoiding locking
+ * where we can.
+ */
+void
+wsdisplay_enter_ddb(void)
+{
+	struct wsdisplay_softc *sc;
+	struct wsscreen *scr;
+
+	if (wsdisplay_console_device != NULL && cn_tab == &wsdisplay_cons) {
+		sc = wsdisplay_console_device;
+		if ((scr = sc->sc_scr[0]) == NULL)
+			return;
+		if (sc->sc_accessops) {
+			(*sc->sc_accessops->enter_ddb)(sc->sc_accesscookie,
+			    scr->scr_dconf->emulcookie);
+		} else {
+			(*sc->sc_accessops->show_screen)(sc->sc_accesscookie,
+			    scr->scr_dconf->emulcookie, 0, NULL, NULL);
+		}
+	}
+}
+
+/*
  * Deal with the xserver doing driver in userland and thus screwing up suspend
  * and resume by switching away from it at suspend/resume time.
  *
diff --git a/sys/dev/wscons/wsdisplayvar.h b/sys/dev/wscons/wsdisplayvar.h
index 9e20834d751..995d09200ea 100644
--- a/sys/dev/wscons/wsdisplayvar.h
+++ b/sys/dev/wscons/wsdisplayvar.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: wsdisplayvar.h,v 1.30 2016/09/04 18:20:34 tedu Exp $ */
+/* $OpenBSD: wsdisplayvar.h,v 1.31 2017/07/19 14:34:10 kettenis Exp $ */
 /* $NetBSD: wsdisplayvar.h,v 1.30 2005/02/04 02:10:49 perry Exp $ */
 
 /*
@@ -145,6 +145,7 @@ struct wsdisplay_accessops {
 	int	(*getchar)(void *, int, int, struct wsdisplay_charcell *);
 	void	(*burn_screen)(void *, u_int, u_int);
 	void	(*pollc)(void *, int);
+	void	(*enter_ddb)(void *, void *);
 };
 
 /* passed to wscons by the video driver to tell about its capabilities */
@@ -229,6 +230,7 @@ int wsdisplay_cfg_ioctl(struct wsdisplay_softc *sc,
  */
 #define WSDISPLAY_NULLSCREEN	-1
 void wsdisplay_switchtoconsole(void);
+void wsdisplay_enter_ddb(void);
 void wsdisplay_suspend(void);
 void wsdisplay_resume(void);
 const struct wsscreen_descr *