tty: vt: expect valid vc when in tty ops

At least since commits feebed65 ("tty: shutdown method") and
bc1e99d9 ("TTY: vt, add ->install"), tty->driver_data in vc is
expected to be set since tty_operations::install() till ::cleanup().

So the checks of !tty->driver_data (aka !vc) in:
* vc_do_resize() by tty -> ioctl(TIOCSWINSZ) -> vt_resize()
* do_con_write() by tty -> tty_operations::write()/::put_char()
* con_flush_chars() by tty -> ::flush_chars()
are all superfluous. And also, holding a console lock is not needed to
fetch tty->driver_data.

Note there is even a stale comment in con_flush_chars() about a race
between that and con_close(). But con_close() does not set
tty->driver_data to NULL for years already.

Drop all these in a hope I am not terribly mistaken.
Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Tested-by: Helge Deller <deller@gmx.de> # parisc STI console
Link: https://lore.kernel.org/r/20240122110401.7289-5-jirislaby@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/vt/vt.c

@@ -1154,9 +1154,6 @@ static int vc_do_resize(struct tty_struct *tty, struct vc_data *vc,
 
 	WARN_CONSOLE_UNLOCKED();
 
-	if (!vc)
-		return -ENXIO;
-
 	user = vc->vc_resize_user;
 	vc->vc_resize_user = 0;
 
@@ -2852,7 +2849,7 @@ static int do_con_write(struct tty_struct *tty, const u8 *buf, int count)
 	};
 	int c, tc, n = 0;
 	unsigned int currcons;
-	struct vc_data *vc;
+	struct vc_data *vc = tty->driver_data;
 	struct vt_notifier_param param;
 	bool rescan;
 
@@ -2860,13 +2857,6 @@ static int do_con_write(struct tty_struct *tty, const u8 *buf, int count)
 		return count;
 
 	console_lock();
-	vc = tty->driver_data;
-	if (vc == NULL) {
-		pr_err("vt: argh, driver_data is NULL !\n");
-		console_unlock();
-		return 0;
-	}
-
 	currcons = vc->vc_num;
 	if (!vc_cons_allocated(currcons)) {
 		/* could this happen? */
@@ -3312,15 +3302,12 @@ static void con_start(struct tty_struct *tty)
 
 static void con_flush_chars(struct tty_struct *tty)
 {
-	struct vc_data *vc;
+	struct vc_data *vc = tty->driver_data;
 
 	if (in_interrupt())	/* from flush_to_ldisc */
 		return;
 
-	/* if we race with con_close(), vt may be null */
 	console_lock();
-	vc = tty->driver_data;
-	if (vc)
 	set_cursor(vc);
 	console_unlock();
 }