2.5: console close race fix

PATCH New Robert Love 1 participant 1 message Jan 25, 2002 Char and misc drivers

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Robert Love

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2002-01-25 23:16 UTC #0 lore raw

PATCH 1/1 2.5: console close race fix

Linus,

There is a race between con_flush_chars and con_close. I first discovered it with the preemptive kernel patch, but it is a general SMP race. The idea for the fix is originally by Andrew Morton.

This fix is in 2.4. Please, apply.

Robert Love

drivers/char/console.c +6 -2

diff -urN linux-2.5.3-pre5/drivers/char/console.c linux/drivers/char/console.c
@@ -2349,14 +2349,18 @@
 
 static void con_flush_chars(struct tty_struct *tty)
 {
-	struct vt_struct *vt = (struct vt_struct *)tty->driver_data;
+	struct vt_struct *vt;
 
 	if (in_interrupt())	/* from flush_to_ldisc */
 		return;
 
 	pm_access(pm_con);
+	
+	/* if we race with con_close(), vt may be null */
 	acquire_console_sem();
-	set_cursor(vt->vc_num);
+	vt = (struct vt_struct *)tty->driver_data;
+	if (vt)
+		set_cursor(vt->vc_num);
 	release_console_sem();
 }