[PATCH] Detaching fbcon: fix give_up_console()

To allow for detaching fbcon, it must be able to give up the console.
However, the function give_up_console() is plain broken.  It just sets the
entries in the console driver map to NULL, it leaves the vt layer without a
console driver, and does not decrement the module reference count.  Calling
give_up_console() is guaranteed to hang the machine..

To fix this problem, ensure that the virtual consoles are not left dangling
without a driver.  All systems have a default boot driver (either vgacon or
dummycon) which is never unloaded.  For those vt's that lost their driver, the
default boot driver is reassigned back to them.

Signed-off-by: Antonino Daplas <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/drivers/char/vt.c b/drivers/char/vt.c
index eb27eed..d7ff7fd 100644 (file)
--- a/drivers/char/vt.c
+++ b/drivers/char/vt.c
@@ -100,6 +100,7 @@
 
 
 const struct consw *conswitchp;
+static struct consw *defcsw; /* default console */
 
 /* A bitmap for codes <32. A bit of 1 indicates that the code
  * corresponding to that bit number invokes some special action
@@ -2673,17 +2674,23 @@ int take_over_console(const struct consw *csw, int first, int last, int deflt)
        if (!try_module_get(owner))
                return -ENODEV;
 
-       acquire_console_sem();
+       /* save default console, for possible recovery later on */
+       if (!defcsw)
+               defcsw = (struct consw *) conswitchp;
 
+       acquire_console_sem();
        desc = csw->con_startup();
+
        if (!desc) {
                release_console_sem();
                module_put(owner);
                return -ENODEV;
        }
+
        if (deflt) {
                if (conswitchp)
                        module_put(conswitchp->owner);
+
                __module_get(owner);
                conswitchp = csw;
        }
@@ -2701,6 +2708,7 @@ int take_over_console(const struct consw *csw, int first, int last, int deflt)
                        continue;
 
                j = i;
+
                if (CON_IS_VISIBLE(vc)) {
                        k = i;
                        save_screen(vc);
@@ -2709,10 +2717,8 @@ int take_over_console(const struct consw *csw, int first, int last, int deflt)
                old_was_color = vc->vc_can_do_color;
                vc->vc_sw->con_deinit(vc);
                vc->vc_origin = (unsigned long)vc->vc_screenbuf;
-               vc->vc_visible_origin = vc->vc_origin;
-               vc->vc_scr_end = vc->vc_origin + vc->vc_screenbuf_size;
-               vc->vc_pos = vc->vc_origin + vc->vc_size_row * vc->vc_y + 2 * vc->vc_x;
                visual_init(vc, i, 0);
+               set_origin(vc);
                update_attr(vc);
 
                /* If the console changed between mono <-> color, then
@@ -2741,22 +2747,29 @@ int take_over_console(const struct consw *csw, int first, int last, int deflt)
                printk("to %s\n", desc);
 
        release_console_sem();
-
        module_put(owner);
        return 0;
 }
 
 void give_up_console(const struct consw *csw)
 {
-       int i;
+       int i, first = -1, last = -1, deflt = 0;
 
-       for(i = 0; i < MAX_NR_CONSOLES; i++)
+       for (i = 0; i < MAX_NR_CONSOLES; i++)
                if (con_driver_map[i] == csw) {
+                       if (first == -1)
+                               first = i;
+                       last = i;
                        module_put(csw->owner);
                        con_driver_map[i] = NULL;
                }
-}
 
+       if (first != -1 && defcsw) {
+               if (first == 0 && last == MAX_NR_CONSOLES - 1)
+                       deflt = 1;
+               take_over_console(defcsw, first, last, deflt);
+       }
+}
 #endif
 
 /*