linux-kernel - [PATCH v3 1/3] virtio_console: Fix locking of vtermno.

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Date:	Tue, 08 Nov 2011 13:44:58 -0800
From:	Miche Baker-Harvey <miche@...gle.com>
To:	Greg Kroah-Hartman <gregkh@...e.de>
Cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	xen-devel@...ts.xensource.com,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Anton Blanchard <anton@...ba.org>,
	Amit Shah <amit.shah@...hat.com>,
	Mike Waychison <mikew@...gle.com>,
	ppc-dev <linuxppc-dev@...ts.ozlabs.org>,
	Eric Northrup <digitaleric@...gle.com>
Subject: [PATCH v3 1/3] virtio_console:  Fix locking of vtermno.

Some modifications of vtermno were not done under the spinlock.

Moved assignment from vtermno and increment of vtermno together,
putting both under the spinlock.  Revert vtermno on failure.

Signed-off-by: Miche Baker-Harvey <miche@...gle.com>
---
 drivers/char/virtio_console.c |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 8e3c46d..9722e76 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -987,18 +987,21 @@ int init_port_console(struct port *port)
 	 * pointers.  The final argument is the output buffer size: we
 	 * can do any size, so we put PAGE_SIZE here.
 	 */
-	port->cons.vtermno = pdrvdata.next_vtermno;
+	spin_lock_irq(&pdrvdata_lock);
+	port->cons.vtermno = pdrvdata.next_vtermno++;
+	spin_unlock_irq(&pdrvdata_lock);
 
 	port->cons.hvc = hvc_alloc(port->cons.vtermno, 0, &hv_ops, PAGE_SIZE);
+	spin_lock_irq(&pdrvdata_lock);
 	if (IS_ERR(port->cons.hvc)) {
 		ret = PTR_ERR(port->cons.hvc);
 		dev_err(port->dev,
 			"error %d allocating hvc for port\n", ret);
 		port->cons.hvc = NULL;
+		port->cons.vtermno = pdrvdata.next_vtermno--;
+		spin_unlock_irq(&pdrvdata_lock);
 		return ret;
 	}
-	spin_lock_irq(&pdrvdata_lock);
-	pdrvdata.next_vtermno++;
 	list_add_tail(&port->cons.list, &pdrvdata.consoles);
 	spin_unlock_irq(&pdrvdata_lock);
 	port->guest_connected = true;

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