From patchwork Thu Jan  8 12:14:18 2009
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Subject: [PATCH 4/4] hvc_console: comment mb and make it an smp_ one
To: Christian Borntraeger <borntraeger@de.ibm.com>,
	Benjiman Herrenschmidt <benh@kernel.crashing.org>
From: Milton Miller <miltonm@bga.com>
Message-Id: <hvc-console-29-3-4@bga.com>
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Date: Thu, 08 Jan 2009 06:14:18 -0600
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Cc: linuxppc-dev list <linuxppc-dev@ozlabs.org>,
	lkml <linux-kernel@vger.kernel.org>, Alan Cox <alan@lxorguk.ukuu.org.uk>
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I remember some history on this barrier.  There was a race between
open via /dev/console and the tty being fully setup.  Its also why
there is a temporary variable and the global is assigned at the end
of the function.

Signed-off-by: Milton Miller <miltonm@bga.com>

Index: work.git/drivers/char/hvc_console.c
===================================================================
--- work.git.orig/drivers/char/hvc_console.c	2009-01-08 04:33:39.000000000 -0600
+++ work.git/drivers/char/hvc_console.c	2009-01-08 04:35:09.000000000 -0600
@@ -875,8 +875,11 @@ static int hvc_init(void)
 		goto stop_thread;
 	}
 
-	/* FIXME: This mb() seems completely random.  Remove it. */
-	mb();
+	/*
+	 * Make sure tty is fully registered before allowing it to be
+	 * found by hvc_console_device.
+	 */
+	smp_mb();
 	hvc_driver = drv;
 	return 0;