[3.8.y.z extended stable] Patch "xen-netback: fix refcnt unbalance for 3.11 and earlier versions" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    xen-netback: fix refcnt unbalance for 3.11 and earlier versions

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.15.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From f78a6f780bfa3bdd192f3849380302fb9fc97533 Mon Sep 17 00:00:00 2001
From: Wei Liu <wei.liu2 at citrix.com>
Date: Thu, 28 Nov 2013 12:48:09 +0000
Subject: xen-netback: fix refcnt unbalance for 3.11 and earlier versions

With the introduction of "xen-netback: Don't destroy the netdev until
the vif is shut down" (upstream commit id 279f438e36), vif disconnect
and free are separated. However in the backported verion reference
counting code was not correctly modified, and the reset of vif->tx_irq
was lost. If frontend goes through vif life cycle more than once the
reference counting is skewed.

This patch adds back the missing tx_irq reset line. It also moves
several lines of the reference counting code to vif_free, so the moved
code corresponds to the counterpart in vif_alloc, thus the reference
counting is balanced.

3.12 and onward versions are not affected by this bug, because reference
counting code was removed due to the introduction of 1:1 model.

This pacth should be backported to all stable verions which are lower
than 3.12 and have 279f438e36.

Reported-and-tested-by: Tomasz Wroblewski <tomasz.wroblewski at citrix.com>
Signed-off-by: Wei Liu <wei.liu2 at citrix.com>
Cc: Ian Campbell <ian.campbell at citrix.com>
Cc: Konrad Wilk <konrad.wilk at oracle.com>
Cc: David Vrabel <david.vrabel at citrix.com>
[ kamal: backport to 3.8 ]
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/net/xen-netback/interface.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
index c63cbd0..b3cbaa9 100644
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -363,17 +363,19 @@ void xenvif_disconnect(struct xenvif *vif)
 	if (netif_carrier_ok(vif->dev))
 		xenvif_carrier_off(vif);

-	atomic_dec(&vif->refcnt);
-	wait_event(vif->waiting_to_free, atomic_read(&vif->refcnt) == 0);
-
-	if (vif->irq)
+	if (vif->irq) {
 		unbind_from_irqhandler(vif->irq, vif);
+		vif->irq = 0;
+	}

 	xen_netbk_unmap_frontend_rings(vif);
 }

 void xenvif_free(struct xenvif *vif)
 {
+	atomic_dec(&vif->refcnt);
+	wait_event(vif->waiting_to_free, atomic_read(&vif->refcnt) == 0);
+
 	unregister_netdev(vif->dev);

 	free_netdev(vif->dev);
--
1.8.3.2