Patch "virtio: console: fix race with port unplug and open/close" has been added to the 3.10-stable tree

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This is a note to let you know that I've just added the patch titled

    virtio: console: fix race with port unplug and open/close

to the 3.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     virtio-console-fix-race-with-port-unplug-and-open-close.patch
and it can be found in the queue-3.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From 057b82be3ca3d066478e43b162fc082930a746c9 Mon Sep 17 00:00:00 2001
From: Amit Shah <amit.shah@xxxxxxxxxx>
Date: Mon, 29 Jul 2013 14:16:13 +0930
Subject: virtio: console: fix race with port unplug and open/close

From: Amit Shah <amit.shah@xxxxxxxxxx>

commit 057b82be3ca3d066478e43b162fc082930a746c9 upstream.

There's a window between find_port_by_devt() returning a port and us
taking a kref on the port, where the port could get unplugged.  Fix it
by taking the reference in find_port_by_devt() itself.

Problem reported and analyzed by Mateusz Guzik.

Reported-by: Mateusz Guzik <mguzik@xxxxxxxxxx>
Signed-off-by: Amit Shah <amit.shah@xxxxxxxxxx>
Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/char/virtio_console.c |   13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -272,9 +272,12 @@ static struct port *find_port_by_devt_in
 	unsigned long flags;
 
 	spin_lock_irqsave(&portdev->ports_lock, flags);
-	list_for_each_entry(port, &portdev->ports, list)
-		if (port->cdev->dev == dev)
+	list_for_each_entry(port, &portdev->ports, list) {
+		if (port->cdev->dev == dev) {
+			kref_get(&port->kref);
 			goto out;
+		}
+	}
 	port = NULL;
 out:
 	spin_unlock_irqrestore(&portdev->ports_lock, flags);
@@ -1036,14 +1039,10 @@ static int port_fops_open(struct inode *
 	struct port *port;
 	int ret;
 
+	/* We get the port with a kref here */
 	port = find_port_by_devt(cdev->dev);
 	filp->private_data = port;
 
-	/* Prevent against a port getting hot-unplugged at the same time */
-	spin_lock_irq(&port->portdev->ports_lock);
-	kref_get(&port->kref);
-	spin_unlock_irq(&port->portdev->ports_lock);
-
 	/*
 	 * Don't allow opening of console port devices -- that's done
 	 * via /dev/hvc


Patches currently in stable-queue which might be from amit.shah@xxxxxxxxxx are

queue-3.10/virtio-console-fix-raising-sigio-after-port-unplug.patch
queue-3.10/virtio-console-clean-up-port-data-immediately-at-time-of-unplug.patch
queue-3.10/virtio-console-quit-from-splice_write-if-pipe-nrbufs-is-0.patch
queue-3.10/virtio-console-fix-race-in-port_fops_open-and-port-unplug.patch
queue-3.10/virtio-console-add-pipe_lock-unlock-for-splice_write.patch
queue-3.10/virtio-console-return-enodev-on-all-read-operations-after-unplug.patch
queue-3.10/virtio-console-fix-race-with-port-unplug-and-open-close.patch
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