Introduce a spinlock for synchronizing access to the video output hardware

in syscons.  This replaces a simple access semaphore that was assumed to be
protected by Giant but often was not.  If two threads that were otherwise
SMP-safe called printf at the same time, there was a high likelyhood that
the semaphore would get corrupted and result in a permanently frozen video
console.  This is similar to what is already done in the serial console
drivers.

3 files changed, 38 insertions, 19 deletions

diff --git a/sys/dev/syscons/scmouse.c b/sys/dev/syscons/scmouse.c
index 73455f3..54ca2ec 100644
--- a/sys/dev/syscons/scmouse.c
+++ b/sys/dev/syscons/scmouse.c
@@ -178,13 +178,13 @@ sc_draw_mouse_image(scr_stat *scp)
     if (ISGRAPHSC(scp))
 	return;
 
-    ++scp->sc->videoio_in_progress;
+    SC_VIDEO_LOCK(scp->sc);
     (*scp->rndr->draw_mouse)(scp, scp->mouse_xpos, scp->mouse_ypos, TRUE);
     scp->mouse_oldpos = scp->mouse_pos;
     scp->mouse_oldxpos = scp->mouse_xpos;
     scp->mouse_oldypos = scp->mouse_ypos;
     scp->status |= MOUSE_VISIBLE;
-    --scp->sc->videoio_in_progress;
+    SC_VIDEO_UNLOCK(scp->sc);
 }
 
 void
@@ -196,7 +196,7 @@ sc_remove_mouse_image(scr_stat *scp)
     if (ISGRAPHSC(scp))
 	return;
 
-    ++scp->sc->videoio_in_progress;
+    SC_VIDEO_LOCK(scp->sc);
     (*scp->rndr->draw_mouse)(scp,
 			     (scp->mouse_oldpos%scp->xsize + scp->xoff)
 			         * scp->font_width,
@@ -217,7 +217,7 @@ sc_remove_mouse_image(scr_stat *scp)
     }
 #endif /* PC98 */
     scp->status &= ~MOUSE_VISIBLE;
-    --scp->sc->videoio_in_progress;
+    SC_VIDEO_UNLOCK(scp->sc);
 }
 
 int
diff --git a/sys/dev/syscons/syscons.c b/sys/dev/syscons/syscons.c
index c42fcf8..08f8e90 100644
--- a/sys/dev/syscons/syscons.c
+++ b/sys/dev/syscons/syscons.c
@@ -1578,7 +1578,7 @@ sccnupdate(scr_stat *scp)
 {
     /* this is a cut-down version of scrn_timer()... */
 
-    if (scp->sc->font_loading_in_progress || scp->sc->videoio_in_progress)
+    if (scp->sc->font_loading_in_progress)
 	return;
 
     if (debugger > 0 || panicstr || shutdown_in_progress) {
@@ -1628,7 +1628,7 @@ scrn_timer(void *arg)
 	return;
 
     /* don't do anything when we are performing some I/O operations */
-    if (sc->font_loading_in_progress || sc->videoio_in_progress) {
+    if (sc->font_loading_in_progress) {
 	if (again)
 	    timeout(scrn_timer, sc, hz / 10);
 	return;
@@ -1722,7 +1722,7 @@ scrn_update(scr_stat *scp, int show_cursor)
 
     /* assert(scp == scp->sc->cur_scp) */
 
-    ++scp->sc->videoio_in_progress;
+    SC_VIDEO_LOCK(scp->sc);
 
 #ifndef SC_NO_CUTPASTE
     /* remove the previous mouse pointer image if necessary */
@@ -1792,7 +1792,7 @@ scrn_update(scr_stat *scp, int show_cursor)
     if (!show_cursor) {
         scp->end = 0;
         scp->start = scp->xsize*scp->ysize - 1;
-	--scp->sc->videoio_in_progress;
+	SC_VIDEO_UNLOCK(scp->sc);
 	return;
     }
 
@@ -1831,7 +1831,7 @@ scrn_update(scr_stat *scp, int show_cursor)
     scp->end = 0;
     scp->start = scp->xsize*scp->ysize - 1;
 
-    --scp->sc->videoio_in_progress;
+    SC_VIDEO_UNLOCK(scp->sc);
 }
 
 #ifdef DEV_SPLASH
@@ -2094,7 +2094,7 @@ sc_switch_scr(sc_softc_t *sc, u_int next_scr)
 
     /* delay switch if the screen is blanked or being updated */
     if ((sc->flags & SC_SCRN_BLANKED) || sc->write_in_progress
-	|| sc->blink_in_progress || sc->videoio_in_progress) {
+	|| sc->blink_in_progress) {
 	sc->delayed_next_scr = next_scr + 1;
 	sc_touch_scrn_saver();
 	DPRINTF(5, ("switch delayed\n"));
@@ -2452,23 +2452,23 @@ void
 sc_draw_cursor_image(scr_stat *scp)
 {
     /* assert(scp == scp->sc->cur_scp); */
-    ++scp->sc->videoio_in_progress;
+    SC_VIDEO_LOCK(scp->sc);
     (*scp->rndr->draw_cursor)(scp, scp->cursor_pos,
 			      scp->curs_attr.flags & CONS_BLINK_CURSOR, TRUE,
 			      sc_inside_cutmark(scp, scp->cursor_pos));
     scp->cursor_oldpos = scp->cursor_pos;
-    --scp->sc->videoio_in_progress;
+    SC_VIDEO_UNLOCK(scp->sc);
 }
 
 void
 sc_remove_cursor_image(scr_stat *scp)
 {
     /* assert(scp == scp->sc->cur_scp); */
-    ++scp->sc->videoio_in_progress;
+    SC_VIDEO_LOCK(scp->sc);
     (*scp->rndr->draw_cursor)(scp, scp->cursor_oldpos,
 			      scp->curs_attr.flags & CONS_BLINK_CURSOR, FALSE,
 			      sc_inside_cutmark(scp, scp->cursor_oldpos));
-    --scp->sc->videoio_in_progress;
+    SC_VIDEO_UNLOCK(scp->sc);
 }
 
 static void
@@ -2499,10 +2499,10 @@ sc_set_cursor_image(scr_stat *scp)
     }
 
     /* assert(scp == scp->sc->cur_scp); */
-    ++scp->sc->videoio_in_progress;
+    SC_VIDEO_LOCK(scp->sc);
     (*scp->rndr->set_cursor)(scp, scp->curs_attr.base, scp->curs_attr.height,
 			     scp->curs_attr.flags & CONS_BLINK_CURSOR);
-    --scp->sc->videoio_in_progress;
+    SC_VIDEO_UNLOCK(scp->sc);
 }
 
 static void
@@ -2606,6 +2606,9 @@ scinit(int unit, int flags)
      * disappeared...
      */
     sc = sc_get_softc(unit, flags & SC_KERNEL_CONSOLE);
+    if ((sc->flags & SC_INIT_DONE) == 0)
+	SC_VIDEO_LOCKINIT(sc);
+
     adp = NULL;
     if (sc->adapter >= 0) {
 	vid_release(sc->adp, (void *)&sc->adapter);
@@ -3458,9 +3461,9 @@ set_mode(scr_stat *scp)
 void
 sc_set_border(scr_stat *scp, int color)
 {
-    ++scp->sc->videoio_in_progress;
+    SC_VIDEO_LOCK(scp->sc);
     (*scp->rndr->draw_border)(scp, color);
-    --scp->sc->videoio_in_progress;
+    SC_VIDEO_UNLOCK(scp->sc);
 }
 
 #ifndef SC_NO_FONT_LOADING
diff --git a/sys/dev/syscons/syscons.h b/sys/dev/syscons/syscons.h
index 1cd33b2..089adf2 100644
--- a/sys/dev/syscons/syscons.h
+++ b/sys/dev/syscons/syscons.h
@@ -34,6 +34,9 @@
 #ifndef _DEV_SYSCONS_SYSCONS_H_
 #define	_DEV_SYSCONS_SYSCONS_H_
 
+#include <sys/lock.h>
+#include <sys/mutex.h>
+
 /* machine-dependent part of the header */
 
 #ifdef PC98
@@ -225,9 +228,9 @@ typedef struct sc_softc {
 
 	char        	font_loading_in_progress;
 	char        	switch_in_progress;
-	char        	videoio_in_progress;
 	char        	write_in_progress;
 	char        	blink_in_progress;
+	struct mtx	video_mtx;
 
 	long		scrn_time_stamp;
 
@@ -532,6 +535,19 @@ typedef struct {
 #define kbd_poll(kbd, on)						\
 		(*kbdsw[(kbd)->kb_index]->poll)((kbd), (on))
 
+#define SC_VIDEO_LOCKINIT(sc)						\
+		mtx_init(&(sc)->video_mtx, "syscons video lock", NULL,MTX_SPIN);
+#define SC_VIDEO_LOCK(sc)						\
+		do {							\
+			if (!cold)					\
+				mtx_lock_spin(&(sc)->video_mtx);	\
+		} while(0)
+#define SC_VIDEO_UNLOCK(sc)						\
+		do {							\
+			if (!cold)					\
+				mtx_unlock_spin(&(sc)->video_mtx);	\
+		} while(0)
+
 /* syscons.c */
 extern int 	(*sc_user_ioctl)(struct cdev *dev, u_long cmd, caddr_t data,
 				 int flag, struct thread *td);