linux-kernel - [patch] vt: bitlock fix

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Message-ID: <20071120051447.GC18332@wotan.suse.de>
Date:	Tue, 20 Nov 2007 06:14:47 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	"Antonino A. Daplas" <adaplas@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [patch] vt: bitlock fix

Don't know who maintains vt.c, but Antonino's name comes up regularly ;)

--
vt is missing a memory barrier to close the critical section. Use a real
spinlock for this.

Signed-off-by: Nick Piggin <npiggin@...e.de>
---
Index: linux-2.6/drivers/char/vt.c
===================================================================
--- linux-2.6.orig/drivers/char/vt.c
+++ linux-2.6/drivers/char/vt.c
@@ -2400,13 +2400,15 @@ static void vt_console_print(struct cons
 {
 	struct vc_data *vc = vc_cons[fg_console].d;
 	unsigned char c;
-	static unsigned long printing;
+	static DEFINE_SPINLOCK(printing_lock);
 	const ushort *start;
 	ushort cnt = 0;
 	ushort myx;
 
 	/* console busy or not yet initialized */
-	if (!printable || test_and_set_bit(0, &printing))
+	if (!printable)
+		return;
+	if (!spin_trylock(&printing_lock))
 		return;
 
 	if (kmsg_redirect && vc_cons_allocated(kmsg_redirect - 1))
@@ -2481,7 +2483,7 @@ static void vt_console_print(struct cons
 	notify_update(vc);
 
 quit:
-	clear_bit(0, &printing);
+	spin_unlock(&printing_lock);
 }
 
 static struct tty_driver *vt_console_device(struct console *c, int *index)
-
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