[PATCH] VT locking fixes

From: Benjamin Herrenschmidt <benh@kernel.crashing.org>

- Make sure that all console operations are approriately protected under
  console_sem.

- Adds checks to make sure that people are taking console_sem when it is
  expected to be held.

drivers/char/selection.c

@@ -24,6 +24,7 @@
 #include <linux/consolemap.h>
 #include <linux/selection.h>
 #include <linux/tiocl.h>
+#include <linux/console.h>
 
 #ifndef MIN
 #define MIN(a,b)	((a) < (b) ? (a) : (b))
@@ -290,7 +291,10 @@ int paste_selection(struct tty_struct *tty)
 	int	pasted = 0, count;
 	DECLARE_WAITQUEUE(wait, current);
 
+	acquire_console_sem();
 	poke_blanked_console();
+	release_console_sem();
+
 	add_wait_queue(&vt->paste_wait, &wait);
 	while (sel_buffer && sel_buffer_lth > pasted) {
 		set_current_state(TASK_INTERRUPTIBLE);

drivers/char/tty_io.c

@@ -1484,7 +1484,12 @@ static int tiocswinsz(struct tty_struct *tty, struct tty_struct *real_tty,
 #ifdef CONFIG_VT
 	if (tty->driver->type == TTY_DRIVER_TYPE_CONSOLE) {
 		unsigned int currcons = tty->index;
-		if (vc_resize(currcons, tmp_ws.ws_col, tmp_ws.ws_row))
+		int rc;
+
+		acquire_console_sem();
+		rc = vc_resize(currcons, tmp_ws.ws_col, tmp_ws.ws_row);
+		release_console_sem();
+		if (rc)
 			return -ENXIO;
 	}
 #endif

drivers/char/vt.c

@@ -148,7 +148,6 @@ static const struct consw *con_driver_map[MAX_NR_CONSOLES];
 static int con_open(struct tty_struct *, struct file *);
 static void vc_init(unsigned int console, unsigned int rows,
 		    unsigned int cols, int do_clear);
-static void blank_screen(unsigned long dummy);
 static void gotoxy(int currcons, int new_x, int new_y);
 static void save_cur(int currcons);
 static void reset_terminal(int currcons, int do_clear);
@@ -156,8 +155,8 @@ static void con_flush_chars(struct tty_struct *tty);
 static void set_vesa_blanking(unsigned long arg);
 static void set_cursor(int currcons);
 static void hide_cursor(int currcons);
-static void unblank_screen_t(unsigned long dummy);
 static void console_callback(void *ignored);
+static void blank_screen_t(unsigned long dummy);
 
 static int printable;		/* Is console ready for printing? */
 
@@ -214,6 +213,13 @@ static int scrollback_delta;
 int (*console_blank_hook)(int);
 
 static struct timer_list console_timer;
+static int blank_state;
+static int blank_timer_expired;
+enum {
+	blank_off = 0,
+	blank_normal_wait,
+	blank_vesa_wait,
+};
 
 /*
  *	Low-Level Functions
@@ -337,6 +343,8 @@ static void do_update_region(int currcons, unsigned long start, int count)
 
 void update_region(int currcons, unsigned long start, int count)
 {
+	WARN_CONSOLE_UNLOCKED();
+
 	if (DO_UPDATE) {
 		hide_cursor(currcons);
 		do_update_region(currcons, start, count);
@@ -400,6 +408,8 @@ void invert_screen(int currcons, int offset, int count, int viewed)
 {
 	unsigned short *p;
 
+	WARN_CONSOLE_UNLOCKED();
+
 	count /= 2;
 	p = screenpos(currcons, offset, viewed);
 	if (sw->con_invert_region)
@@ -445,6 +455,8 @@ void complement_pos(int currcons, int offset)
 	static unsigned short old;
 	static unsigned short oldx, oldy;
 
+	WARN_CONSOLE_UNLOCKED();
+
 	if (p) {
 		scr_writew(old, p);
 		if (DO_UPDATE)
@@ -564,6 +576,8 @@ static void set_cursor(int currcons)
 
 static void set_origin(int currcons)
 {
+	WARN_CONSOLE_UNLOCKED();
+
 	if (!IS_VISIBLE ||
 	    !sw->con_set_origin ||
 	    !sw->con_set_origin(vc_cons[currcons].d))
@@ -575,6 +589,8 @@ static void set_origin(int currcons)
 
 static inline void save_screen(int currcons)
 {
+	WARN_CONSOLE_UNLOCKED();
+
 	if (sw->con_save_screen)
 		sw->con_save_screen(vc_cons[currcons].d);
 }
@@ -588,6 +604,8 @@ void redraw_screen(int new_console, int is_switch)
 	int redraw = 1;
 	int currcons, old_console;
 
+	WARN_CONSOLE_UNLOCKED();
+
 	if (!vc_cons_allocated(new_console)) {
 		/* strange ... */
 		/* printk("redraw_screen: tty %d not allocated ??\n", new_console+1); */
@@ -665,6 +683,8 @@ static void visual_init(int currcons, int init)
 
 int vc_allocate(unsigned int currcons)	/* return 0 on success */
 {
+	WARN_CONSOLE_UNLOCKED();
+
 	if (currcons >= MAX_NR_CONSOLES)
 		return -ENXIO;
 	if (!vc_cons[currcons].d) {
@@ -731,6 +751,8 @@ int vc_resize(int currcons, unsigned int cols, unsigned int lines)
 	unsigned int new_cols, new_rows, new_row_size, new_screen_size;
 	unsigned short *newscreen;
 
+	WARN_CONSOLE_UNLOCKED();
+
 	if (!vc_cons_allocated(currcons))
 		return -ENXIO;
 
@@ -817,7 +839,8 @@ int vc_resize(int currcons, unsigned int cols, unsigned int lines)
 
 void vc_disallocate(unsigned int currcons)
 {
-	acquire_console_sem();
+	WARN_CONSOLE_UNLOCKED();
+
 	if (vc_cons_allocated(currcons)) {
 	    sw->con_deinit(vc_cons[currcons].d);
 	    if (kmalloced)
@@ -826,7 +849,6 @@ void vc_disallocate(unsigned int currcons)
 		kfree(vc_cons[currcons].d);
 	    vc_cons[currcons].d = NULL;
 	}
-	release_console_sem();
 }
 
 /*
@@ -2081,6 +2103,10 @@ static void console_callback(void *ignored)
 			sw->con_scrolldelta(vc_cons[currcons].d, scrollback_delta);
 		scrollback_delta = 0;
 	}
+	if (blank_timer_expired) {
+		do_blank_screen(0);
+		blank_timer_expired = 0;
+	}
 
 	release_console_sem();
 }
@@ -2414,7 +2440,9 @@ static int con_open(struct tty_struct *tty, struct file * filp)
 
 	currcons = tty->index;
 
+	acquire_console_sem();
 	i = vc_allocate(currcons);
+	release_console_sem();
 	if (i)
 		return i;
 
@@ -2480,16 +2508,20 @@ static int __init con_init(void)
 	const char *display_desc = NULL;
 	unsigned int currcons = 0;
 
+	acquire_console_sem();
+
 	if (conswitchp)
 		display_desc = conswitchp->con_startup();
 	if (!display_desc) {
 		fg_console = 0;
+		release_console_sem();
 		return 0;
 	}
 
 	init_timer(&console_timer);
-	console_timer.function = blank_screen;
+	console_timer.function = blank_screen_t;
 	if (blankinterval) {
+		blank_state = blank_normal_wait;
 		mod_timer(&console_timer, jiffies + blankinterval);
 	}
 
@@ -2520,6 +2552,8 @@ static int __init con_init(void)
 	printable = 1;
 	printk("\n");
 
+	release_console_sem();
+
 #ifdef CONFIG_VT_CONSOLE
 	register_console(&vt_console_driver);
 #endif
@@ -2599,8 +2633,13 @@ void take_over_console(const struct consw *csw, int first, int last, int deflt)
 	int i, j = -1;
 	const char *desc;
 
+	acquire_console_sem();
+
 	desc = csw->con_startup();
-	if (!desc) return;
+	if (!desc) {
+		release_console_sem();
+		return;
+	}
 	if (deflt)
 		conswitchp = csw;
 
@@ -2640,6 +2679,8 @@ void take_over_console(const struct consw *csw, int first, int last, int deflt)
 		       desc, vc_cons[j].d->vc_cols, vc_cons[j].d->vc_rows);
 	else
 		printk("to %s\n", desc);
+
+	release_console_sem();
 }
 
 void give_up_console(const struct consw *csw)
@@ -2688,23 +2729,24 @@ static void vesa_powerdown(void)
     }
 }
 
-/*
- * This is a timer handler
- */
-static void vesa_powerdown_screen(unsigned long dummy)
-{
-	console_timer.function = unblank_screen_t;
-
-	vesa_powerdown();
-}
-
-static void timer_do_blank_screen(int entering_gfx, int from_timer_handler)
+void do_blank_screen(int entering_gfx)
 {
 	int currcons = fg_console;
 	int i;
 
-	if (console_blanked)
+	WARN_CONSOLE_UNLOCKED();
+
+	if (console_blanked) {
+		if (blank_state == blank_vesa_wait) {
+			blank_state = blank_off;
+			vesa_powerdown();
+
+		}
 		return;
+	}
+	if (blank_state != blank_normal_wait)
+		return;
+	blank_state = blank_off;
 
 	/* entering graphics mode? */
 	if (entering_gfx) {
@@ -2723,9 +2765,8 @@ static void timer_do_blank_screen(int entering_gfx, int from_timer_handler)
 	}
 
 	hide_cursor(currcons);
-	if (!from_timer_handler)
 	del_timer_sync(&console_timer);
-	console_timer.function = unblank_screen_t;
+	blank_timer_expired = 0;
 
 	save_screen(currcons);
 	/* In case we need to reset origin, blanking hook returns 1 */
@@ -2738,7 +2779,7 @@ static void timer_do_blank_screen(int entering_gfx, int from_timer_handler)
 		return;
 
 	if (vesa_off_interval) {
-		console_timer.function = vesa_powerdown_screen;
+		blank_state = blank_vesa_wait,
 		mod_timer(&console_timer, jiffies + vesa_off_interval);
 	}
 
@@ -2746,18 +2787,6 @@ static void timer_do_blank_screen(int entering_gfx, int from_timer_handler)
 		sw->con_blank(vc_cons[currcons].d, vesa_blank_mode + 1);
 }
 
-void do_blank_screen(int entering_gfx)
-{
-	timer_do_blank_screen(entering_gfx, 0);
-}
-
-/*
- * This is a timer handler
- */
-static void unblank_screen_t(unsigned long dummy)
-{
-	unblank_screen();
-}
 
 /*
  * Called by timer as well as from vt_console_driver
@@ -2766,6 +2795,8 @@ void unblank_screen(void)
 {
 	int currcons;
 
+	WARN_CONSOLE_UNLOCKED();
+
 	ignore_poke = 0;
 	if (!console_blanked)
 		return;
@@ -2778,9 +2809,9 @@ void unblank_screen(void)
 	if (vcmode != KD_TEXT)
 		return; /* but leave console_blanked != 0 */
 
-	console_timer.function = blank_screen;
 	if (blankinterval) {
 		mod_timer(&console_timer, jiffies + blankinterval);
+		blank_state = blank_normal_wait;
 	}
 
 	console_blanked = 0;
@@ -2794,23 +2825,33 @@ void unblank_screen(void)
 }
 
 /*
- * This is both a user-level callable and a timer handler
+ * We defer the timer blanking to work queue so it can take the console semaphore
+ * (console operations can still happen at irq time, but only from printk which
+ * has the console semaphore. Not perfect yet, but better than no locking
  */
-static void blank_screen(unsigned long dummy)
+static void blank_screen_t(unsigned long dummy)
 {
-	timer_do_blank_screen(0, 1);
+	blank_timer_expired = 1;
+	schedule_work(&console_work);
 }
 
 void poke_blanked_console(void)
 {
+	WARN_CONSOLE_UNLOCKED();
+
+	/* This isn't perfectly race free, but a race here would be mostly harmless,
+	 * at worse, we'll do a spurrious blank and it's unlikely
+	 */
 	del_timer(&console_timer);
+	blank_timer_expired = 0;
+
 	if (ignore_poke || !vt_cons[fg_console] || vt_cons[fg_console]->vc_mode == KD_GRAPHICS)
 		return;
-	if (console_blanked) {
-		console_timer.function = unblank_screen_t;
-		mod_timer(&console_timer, jiffies);	/* Now */
-	} else if (blankinterval) {
+	if (console_blanked)
+		unblank_screen();
+	else if (blankinterval) {
 		mod_timer(&console_timer, jiffies + blankinterval);
+		blank_state = blank_normal_wait;
 	}
 }
 
@@ -2820,6 +2861,8 @@ void poke_blanked_console(void)
 
 void set_palette(int currcons)
 {
+	WARN_CONSOLE_UNLOCKED();
+
 	if (vcmode != KD_GRAPHICS)
 		sw->con_set_palette(vc_cons[currcons].d, color_table);
 }
@@ -2828,6 +2871,8 @@ static int set_get_cmap(unsigned char *arg, int set)
 {
     int i, j, k;
 
+    WARN_CONSOLE_UNLOCKED();
+
     for (i = 0; i < 16; i++)
 	if (set) {
 	    get_user(default_red[i], arg++);
@@ -2859,12 +2904,24 @@ static int set_get_cmap(unsigned char *arg, int set)
 
 int con_set_cmap(unsigned char *arg)
 {
-	return set_get_cmap (arg,1);
+	int rc;
+
+	acquire_console_sem();
+	rc = set_get_cmap (arg,1);
+	release_console_sem();
+
+	return rc;
 }
 
 int con_get_cmap(unsigned char *arg)
 {
-	return set_get_cmap (arg,0);
+	int rc;
+
+	acquire_console_sem();
+	rc = set_get_cmap (arg,0);
+	release_console_sem();
+
+	return rc;
 }
 
 void reset_palette(int currcons)
@@ -2938,8 +2995,12 @@ int con_font_op(int currcons, struct console_font_op *op)
 		set = 1;
 	} else if (op->op == KD_FONT_OP_GET)
 		set = 0;
-	else
-		return sw->con_font_op(vc_cons[currcons].d, op);
+	else {
+		acquire_console_sem();
+		rc = sw->con_font_op(vc_cons[currcons].d, op);
+		release_console_sem();
+		return rc;
+	}
 	if (op->data) {
 		temp = kmalloc(size, GFP_KERNEL);
 		if (!temp)
@@ -3034,10 +3095,14 @@ static int pm_con_request(struct pm_dev *dev, pm_request_t rqst, void *data)
 	switch (rqst)
 	{
 	case PM_RESUME:
+		acquire_console_sem();
 		unblank_screen();
+		release_console_sem();
 		break;
 	case PM_SUSPEND:
+		acquire_console_sem();
 		do_blank_screen(0);
+		release_console_sem();
 		break;
 	}
 	return 0;

drivers/char/vt_ioctl.c

@@ -470,6 +470,9 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
 		 * currently, setting the mode from KD_TEXT to KD_GRAPHICS
 		 * doesn't do a whole lot. i'm not sure if it should do any
 		 * restoration of modes or what...
+		 *
+		 * XXX It should at least call into the driver, fbdev's definitely
+		 * need to restore their engine state. --BenH
 		 */
 		if (!perm)
 			return -EPERM;
@@ -492,10 +495,12 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
 		/*
 		 * explicitly blank/unblank the screen if switching modes
 		 */
+		acquire_console_sem();
 		if (arg == KD_TEXT)
 			unblank_screen();
 		else
 			do_blank_screen(1);
+		release_console_sem();
 		return 0;
 
 	case KDGETMODE:
@@ -665,18 +670,29 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
 			return -EFAULT;
 		if (tmp.mode != VT_AUTO && tmp.mode != VT_PROCESS)
 			return -EINVAL;
+		acquire_console_sem();
 		vt_cons[console]->vt_mode = tmp;
 		/* the frsig is ignored, so we set it to 0 */
 		vt_cons[console]->vt_mode.frsig = 0;
 		vt_cons[console]->vt_pid = current->pid;
 		/* no switch is required -- saw@shade.msu.ru */
 		vt_cons[console]->vt_newvt = -1; 
+		release_console_sem();
 		return 0;
 	}
 
 	case VT_GETMODE:
-		return copy_to_user((void*)arg, &(vt_cons[console]->vt_mode), 
-							sizeof(struct vt_mode)) ? -EFAULT : 0; 
+	{
+		struct vt_mode tmp;
+		int rc;
+
+		acquire_console_sem();
+		memcpy(&tmp, &vt_cons[console]->vt_mode, sizeof(struct vt_mode));
+		release_console_sem();
+
+		rc = copy_to_user((void*)arg, &tmp, sizeof(struct vt_mode));
+		return rc ? -EFAULT : 0;
+	}
 
 	/*
 	 * Returns global vt state. Note that VT 0 is always open, since
@@ -718,7 +734,9 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
 		if (arg == 0 || arg > MAX_NR_CONSOLES)
 			return -ENXIO;
 		arg--;
+		acquire_console_sem();
 		i = vc_allocate(arg);
+		release_console_sem();
 		if (i)
 			return i;
 		set_console(arg);
@@ -768,17 +786,20 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
 				 * The current vt has been released, so
 				 * complete the switch.
 				 */
-				int newvt = vt_cons[console]->vt_newvt;
+				int newvt;
+				acquire_console_sem();
+				newvt = vt_cons[console]->vt_newvt;
 				vt_cons[console]->vt_newvt = -1;
 				i = vc_allocate(newvt);
-				if (i)
+				if (i) {
+					release_console_sem();
 					return i;
+				}
 				/*
 				 * When we actually do the console switch,
 				 * make sure we are atomic with respect to
 				 * other console switches..
 				 */
-				acquire_console_sem();
 				complete_change_console(newvt);
 				release_console_sem();
 			}
@@ -806,16 +827,21 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
 			return -ENXIO;
 		if (arg == 0) {
 		    /* disallocate all unused consoles, but leave 0 */
+			acquire_console_sem();
 			for (i=1; i<MAX_NR_CONSOLES; i++)
 				if (! VT_BUSY(i))
 					vc_disallocate(i);
+			release_console_sem();
 		} else {
 			/* disallocate a single console, if possible */
 			arg--;
 			if (VT_BUSY(arg))
 				return -EBUSY;
-		    if (arg)			      /* leave 0 */
+			if (arg) {			      /* leave 0 */
+				acquire_console_sem();
 				vc_disallocate(arg);
+				release_console_sem();
+			}
 		}
 		return 0;
 
@@ -828,8 +854,11 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
 		if (get_user(ll, &vtsizes->v_rows) ||
 		    get_user(cc, &vtsizes->v_cols))
 			return -EFAULT;
-		for (i = 0; i < MAX_NR_CONSOLES; i++)
+		for (i = 0; i < MAX_NR_CONSOLES; i++) {
+			acquire_console_sem();
                         vc_resize(i, cc, ll);
+			release_console_sem();
+		}
 		return 0;
 	}
 
@@ -870,11 +899,13 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
 		for (i = 0; i < MAX_NR_CONSOLES; i++) {
 			if (!vc_cons[i].d)
 				continue;
+			acquire_console_sem();
 			if (vlin)
 				vc_cons[i].d->vc_scan_lines = vlin;
 			if (clin)
 				vc_cons[i].d->vc_font.height = clin;
 			vc_resize(i, cc, ll);
+			release_console_sem();
 		}
   		return 0;
 	}

include/linux/console.h

@@ -102,6 +102,14 @@ extern void acquire_console_sem(void);
 extern void release_console_sem(void);
 extern void console_conditional_schedule(void);
 extern void console_unblank(void);
+extern int is_console_locked(void);
+
+/* Some debug stub to catch some of the obvious races in the VT code */
+#if 1
+#define WARN_CONSOLE_UNLOCKED()	WARN_ON(!is_console_locked() && !oops_in_progress)
+#else
+#define WARN_CONSOLE_UNLOCKED()
+#endif
 
 /* VESA Blanking Levels */
 #define VESA_NO_BLANKING        0

kernel/power/console.c

@@ -6,6 +6,7 @@
 
 #include <linux/vt_kern.h>
 #include <linux/kbd_kern.h>
+#include <linux/console.h>
 #include "power.h"
 
 static int new_loglevel = 10;
@@ -18,14 +19,20 @@ int pm_prepare_console(void)
 	console_loglevel = new_loglevel;
 
 #ifdef SUSPEND_CONSOLE
+	acquire_console_sem();
+
 	orig_fgconsole = fg_console;
 
-	if (vc_allocate(SUSPEND_CONSOLE))
+	if (vc_allocate(SUSPEND_CONSOLE)) {
 	  /* we can't have a free VC for now. Too bad,
 	   * we don't want to mess the screen for now. */
+		release_console_sem();
 		return 1;
+	}
 
 	set_console(SUSPEND_CONSOLE);
+	release_console_sem();
+
 	if (vt_waitactive(SUSPEND_CONSOLE)) {
 		pr_debug("Suspend: Can't switch VCs.");
 		return 1;
@@ -40,12 +47,9 @@ void pm_restore_console(void)
 {
 	console_loglevel = orig_loglevel;
 #ifdef SUSPEND_CONSOLE
+	acquire_console_sem();
 	set_console(orig_fgconsole);
-
-	/* FIXME: 
-	 * This following part is left over from swsusp. Is it really needed?
-	 */
-	update_screen(fg_console);
+	release_console_sem();
 #endif
 	return;
 }

kernel/printk.c

@@ -62,6 +62,15 @@ int oops_in_progress;
  */
 static DECLARE_MUTEX(console_sem);
 struct console *console_drivers;
+/*
+ * This is used for debugging the mess that is the VT code by
+ * keeping track if we have the console semaphore held. It's
+ * definitely not the perfect debug tool (we don't know if _WE_
+ * hold it are racing, but it helps tracking those weird code
+ * path in the console code where we end up in places I want
+ * locked without the console sempahore held
+ */
+static int console_locked;
 
 /*
  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
@@ -524,6 +533,7 @@ asmlinkage int printk(const char *fmt, ...)
 		goto out;
 	}
 	if (!down_trylock(&console_sem)) {
+		console_locked = 1;
 		/*
 		 * We own the drivers.  We can drop the spinlock and let
 		 * release_console_sem() print the text
@@ -557,10 +567,17 @@ void acquire_console_sem(void)
 	if (in_interrupt())
 		BUG();
 	down(&console_sem);
+	console_locked = 1;
 	console_may_schedule = 1;
 }
 EXPORT_SYMBOL(acquire_console_sem);
 
+int is_console_locked(void)
+{
+	return console_locked;
+}
+EXPORT_SYMBOL(is_console_locked);
+
 /**
  * release_console_sem - unlock the console system
  *
@@ -592,12 +609,14 @@ void release_console_sem(void)
 		spin_unlock_irqrestore(&logbuf_lock, flags);
 		call_console_drivers(_con_start, _log_end);
 	}
+	console_locked = 0;
 	console_may_schedule = 0;
 	up(&console_sem);
 	spin_unlock_irqrestore(&logbuf_lock, flags);
 	if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
 		wake_up_interruptible(&log_wait);
 }
+EXPORT_SYMBOL(release_console_sem);
 
 /** console_conditional_schedule - yield the CPU if required
  *
@@ -633,6 +652,7 @@ void console_unblank(void)
 	 */
 	if (down_trylock(&console_sem) != 0)
 		return;
+	console_locked = 1;
 	console_may_schedule = 0;
 	for (c = console_drivers; c != NULL; c = c->next)
 		if ((c->flags & CON_ENABLED) && c->unblank)