On Mon, Jun 22, 2015 at 02:40:43PM +1000, Dave Airlie wrote:
> From: Dave Airlie <airlied at redhat.com>
>
> We should validate the passed in mstb under the lock
> this should stop us getting an invalid mstb here.
>
> (first attempt with cancelling work has lockdep issues).
> Bugzilla: https://bugs.archlinux.org/task/45369
>
> v2: update bugzilla, add some notes on why passing mst_primary
> is okay.
>
> Signed-off-by: Dave Airlie <airlied at redhat.com>
On 2nd look I realized that pulling out mgr->lock and using the _locked
variant won't work cleanly since the _put might also take the mgr->lock. I
guess we could fix that too by also pulling the ref grab/drop for its
argument out of check_and_send like this:
diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
b/drivers/gpu/drm/drm_dp_mst_topology.c
index 132581ca4ad8..08c131536b2b 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -1189,6 +1189,7 @@ static void drm_dp_check_and_send_link_address(struct
drm_dp_mst_topology_mgr *m
struct drm_dp_mst_branch *mstb)
{
struct drm_dp_mst_port *port;
+ struct drm_dp_mst_branch *mstb_child;
if (!mstb->link_address_sent) {
drm_dp_send_link_address(mgr, mstb);
@@ -1204,17 +1205,31 @@ static void drm_dp_check_and_send_link_address(struct
drm_dp_mst_topology_mgr *m
if (!port->available_pbn)
drm_dp_send_enum_path_resources(mgr, mstb, port);
- if (port->mstb)
- drm_dp_check_and_send_link_address(mgr, port->mstb);
+ if (port->mstb) {
+ mstb_child = drm_dp_get_validated_mstb_ref(mgr,
+ port->mstb);
+ if (mstb_child) {
+ drm_dp_check_and_send_link_address(mgr,
+ mstb_child);
+ drm_dp_put_mst_branch_device(mstb_child);
+ }
+ }
}
}
static void drm_dp_mst_link_probe_work(struct work_struct *work)
{
struct drm_dp_mst_topology_mgr *mgr = container_of(work, struct
drm_dp_mst_topology_mgr, work);
+ struct drm_dp_mst_branch *mstb;
- drm_dp_check_and_send_link_address(mgr, mgr->mst_primary);
+ mutex_lock(&mgr->lock);
+ kref_get(&mgr->mst_primary->kref);
+ mstb = mgr->mst_primary;
+ mutex_unlock(&mgr->lock);
+ drm_dp_check_and_send_link_address(mgr, mstb);
+
+ drm_dp_put_mst_branch_device(mstb);
}
static bool drm_dp_validate_guid(struct drm_dp_mst_topology_mgr *mgr,
Upside is that we don't need a comment, and imo non-tricky code is better
code. Or am I still missing something?
-Daniel
> ---
> drivers/gpu/drm/drm_dp_mst_topology.c | 17 +++++++++++++++--
> 1 file changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> b/drivers/gpu/drm/drm_dp_mst_topology.c
> index fb65f5d..3c7e5cd 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -1198,9 +1198,14 @@ static struct drm_dp_mst_branch
> *drm_dp_get_mst_branch_device(struct drm_dp_mst_
> }
>
> static void drm_dp_check_and_send_link_address(struct
> drm_dp_mst_topology_mgr *mgr,
> - struct drm_dp_mst_branch *mstb)
> + struct drm_dp_mst_branch
> *mstb_in)
> {
> struct drm_dp_mst_port *port;
> + struct drm_dp_mst_branch *mstb;
> +
> + mstb = drm_dp_get_validated_mstb_ref(mgr, mstb_in);
> + if (!mstb)
> + return;
>
> if (!mstb->link_address_sent) {
> drm_dp_send_link_address(mgr, mstb);
> @@ -1219,12 +1224,20 @@ static void drm_dp_check_and_send_link_address(struct
> drm_dp_mst_topology_mgr *m
> if (port->mstb)
> drm_dp_check_and_send_link_address(mgr, port->mstb);
> }
> + drm_dp_put_mst_branch_device(mstb);
> }
>
> static void drm_dp_mst_link_probe_work(struct work_struct *work)
> {
> struct drm_dp_mst_topology_mgr *mgr = container_of(work, struct
> drm_dp_mst_topology_mgr, work);
> -
> + /*
> + * Note this passes mgr->mst_primary without validation
> + * it could be a) valid, b) NULL, c) some value between
> + * since we haven't taken the lock,
> + * however the validation sequence in check and send
> + * will take the lock, and if the value isn't valid
> + * it will fail appropriately.
> + */
> drm_dp_check_and_send_link_address(mgr, mgr->mst_primary);
>
> }
> --
> 2.4.1
>
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--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
