[3.19.y-ckt stable] Patch "drm/dp/mst: take lock around looking up the branch device on hpd irq" has been added to staging queue

[Kamal Mostafa]

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

    drm/dp/mst: take lock around looking up the branch device on hpd irq

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.y-ckt4.

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

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From c02eaf6be4404d14a4488b7f4d7ad60602831020 Mon Sep 17 00:00:00 2001
From: Dave Airlie <airlied at redhat.com>
Date: Mon, 22 Jun 2015 14:40:44 +1000
Subject: drm/dp/mst: take lock around looking up the branch device on hpd irq

commit 9eb1e57f564d4e6e10991402726cc83fe0b9172f upstream.

If we are doing an MST transaction and we've gotten HPD and we
lookup the device from the incoming msg, we should take the mgr
lock around it, so that mst_primary and mstb->ports are valid.

Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Signed-off-by: Dave Airlie <airlied at redhat.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index e0da405..4d7a4d9 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -1159,6 +1159,8 @@ static struct drm_dp_mst_branch *drm_dp_get_mst_branch_device(struct drm_dp_mst_
 	struct drm_dp_mst_port *port;
 	int i;
 	/* find the port by iterating down */
+
+	mutex_lock(&mgr->lock);
 	mstb = mgr->mst_primary;

 	for (i = 0; i < lct - 1; i++) {
@@ -1178,6 +1180,7 @@ static struct drm_dp_mst_branch *drm_dp_get_mst_branch_device(struct drm_dp_mst_
 		}
 	}
 	kref_get(&mstb->kref);
+	mutex_unlock(&mgr->lock);
 	return mstb;
 }

--
1.9.1