1 files changed, 62 insertions, 6 deletions

diff --git a/sys/dev/syscons/syscons.c b/sys/dev/syscons/syscons.c
index 7333b3c7c1cee..30c7a1a1327d0 100644
--- a/sys/dev/syscons/syscons.c
+++ b/sys/dev/syscons/syscons.c
@@ -1678,13 +1678,39 @@ sccnkbdunlock(sc_softc_t *sc, struct sc_cnstate *sp)
 static void
 sccnscrlock(sc_softc_t *sc, struct sc_cnstate *sp)
 {
-    SC_VIDEO_LOCK(sc);
+    int retries;
+
+    /**
+     * Locking method:
+     * - if kdb_active and video_mtx is not owned by anyone, then lock
+     *   by kdb remaining active
+     * - if !kdb_active, try to acquire video_mtx without blocking or
+     *   recursing; if we get it then it works normally.
+     * Note that video_mtx is especially unusable if we already own it,
+     * since then it is protecting something and syscons is not reentrant
+     * enough to ignore the protection even in the kdb_active case.
+     */
+    if (kdb_active) {
+	sp->kdb_locked = sc->video_mtx.mtx_lock == MTX_UNOWNED || panicstr;
+	sp->mtx_locked = FALSE;
+    } else {
+	sp->kdb_locked = FALSE;
+	for (retries = 0; retries < 1000; retries++) {
+	    sp->mtx_locked = mtx_trylock_spin_flags(&sc->video_mtx,
+		MTX_QUIET) != 0 || panicstr;
+	    if (sp->mtx_locked)
+		break;
+	    DELAY(1);
+	}
+    }
 }
 
 static void
 sccnscrunlock(sc_softc_t *sc, struct sc_cnstate *sp)
 {
-    SC_VIDEO_UNLOCK(sc);
+    if (sp->mtx_locked)
+	mtx_unlock_spin(&sc->video_mtx);
+    sp->mtx_locked = sp->kdb_locked = FALSE;
 }
 
 static void
@@ -1721,6 +1747,8 @@ over_keyboard: ;
 
     /* The screen is opened iff locking it succeeds. */
     sccnscrlock(sc, sp);
+    if (!sp->kdb_locked && !sp->mtx_locked)
+	return;
     sp->scr_opened = TRUE;
 
     /* The screen switch is optional. */
@@ -1797,6 +1825,10 @@ sc_cnungrab(struct consdev *cp)
     atomic_add_int(&sc->grab_level, -1);
 }
 
+static char sc_cnputc_log[0x1000];
+static u_int sc_cnputc_loghead;
+static u_int sc_cnputc_logtail;
+
 static void
 sc_cnputc(struct consdev *cd, int c)
 {
@@ -1808,12 +1840,28 @@ sc_cnputc(struct consdev *cd, int c)
     struct tty *tp;
 #endif
 #endif /* !SC_NO_HISTORY */
+    u_int head;
     int s;
 
     /* assert(sc_console != NULL) */
 
     sccnopen(scp->sc, &st, 0);
 
+    /*
+     * Log the output.
+     *
+     * In the unlocked case, the logging is intentionally only
+     * perfectly atomic for the indexes.
+     */
+    head = atomic_fetchadd_int(&sc_cnputc_loghead, 1);
+    sc_cnputc_log[head % sizeof(sc_cnputc_log)] = c;
+
+    /*
+     * If we couldn't open, return to defer output.
+     */
+    if (!st.scr_opened)
+	return;
+
 #ifndef SC_NO_HISTORY
     if (scp == scp->sc->cur_scp && scp->status & SLKED) {
 	scp->status &= ~SLKED;
@@ -1841,8 +1889,14 @@ sc_cnputc(struct consdev *cd, int c)
     }
 #endif /* !SC_NO_HISTORY */
 
-    buf[0] = c;
-    sc_puts(scp, buf, 1, 1);
+    /* Play any output still in the log (our char may already be done). */
+    while (sc_cnputc_logtail != atomic_load_acq_int(&sc_cnputc_loghead)) {
+	buf[0] = sc_cnputc_log[sc_cnputc_logtail++ % sizeof(sc_cnputc_log)];
+	if (atomic_load_acq_int(&sc_cnputc_loghead) - sc_cnputc_logtail >=
+	    sizeof(sc_cnputc_log))
+	    continue;
+	sc_puts(scp, buf, 1, 1);
+    }
 
     s = spltty();	/* block sckbdevent and scrn_timer */
     sccnupdate(scp);
@@ -1883,9 +1937,11 @@ sc_cngetc_locked(struct sc_cnstate *sp)
      * Stop the screen saver and update the screen if necessary.
      * What if we have been running in the screen saver code... XXX
      */
-    sc_touch_scrn_saver();
+    if (sp->scr_opened)
+	sc_touch_scrn_saver();
     scp = sc_console->sc->cur_scp;	/* XXX */
-    sccnupdate(scp);
+    if (sp->scr_opened)
+	sccnupdate(scp);
 
     if (fkeycp < fkey.len)
 	return fkey.str[fkeycp++];