Re: [PATCH v2 20/27] drm/dp_mst: Protect drm_dp_mst_port members with connection_mutex

Lyude Paul
2019-09-25T21:01:39Z

On Wed, 2019-09-25 at 16:00 -0400, Sean Paul wrote:
> On Tue, Sep 03, 2019 at 04:45:58PM -0400, Lyude Paul wrote:
> > Yes-you read that right. Currently there is literally no locking in
> > place for any of the drm_dp_mst_port struct members that can be modified
> > in response to a link address response, or a connection status response.
> > Which literally means if we're unlucky enough to have any sort of
> > hotplugging event happen before we're finished with reprobing link
> > addresses, we'll race and the contents of said struct members becomes
> > undefined. Fun!
> >
> > So, finally add some simple locking protections to our MST helpers by
> > protecting any drm_dp_mst_port members which can be changed by link
> > address responses or connection status notifications under
> > drm_device->mode_config.connection_mutex.
> >
> > Cc: Juston Li <juston.li@intel.com>
> > Cc: Imre Deak <imre.deak@intel.com>
> > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > Cc: Harry Wentland <hwentlan@amd.com>
> > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> > Signed-off-by: Lyude Paul <lyude@redhat.com>
> > ---
> > drivers/gpu/drm/drm_dp_mst_topology.c | 144 +++++++++++++++++++-------
> > include/drm/drm_dp_mst_helper.h | 39 +++++--
> > 2 files changed, 133 insertions(+), 50 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> > b/drivers/gpu/drm/drm_dp_mst_topology.c
> > index 5101eeab4485..259634c5d6dc 100644
> > --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> > +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> > @@ -1354,6 +1354,7 @@ static void drm_dp_free_mst_port(struct kref *kref)
> > container_of(kref, struct drm_dp_mst_port, malloc_kref);
> >
> > drm_dp_mst_put_mstb_malloc(port->parent);
> > + mutex_destroy(&port->lock);
> > kfree(port);
> > }
> >
> > @@ -1906,6 +1907,36 @@ void drm_dp_mst_connector_early_unregister(struct
> > drm_connector *connector,
> > }
> > EXPORT_SYMBOL(drm_dp_mst_connector_early_unregister);
> >
> > +static void
> > +drm_dp_mst_port_add_connector(struct drm_dp_mst_branch *mstb,
> > + struct drm_dp_mst_port *port)
> > +{
> > + struct drm_dp_mst_topology_mgr *mgr = port->mgr;
> > + char proppath[255];
> > + int ret;
> > +
> > + build_mst_prop_path(mstb, port->port_num, proppath, sizeof(proppath));
> > + port->connector = mgr->cbs->add_connector(mgr, port, proppath);
> > + if (!port->connector) {
> > + ret = -ENOMEM;
> > + goto error;
> > + }
> > +
> > + if ((port->pdt == DP_PEER_DEVICE_DP_LEGACY_CONV ||
> > + port->pdt == DP_PEER_DEVICE_SST_SINK) &&
> > + port->port_num >= DP_MST_LOGICAL_PORT_0) {
> > + port->cached_edid = drm_get_edid(port->connector,
> > + &port->aux.ddc);
> > + drm_connector_set_tile_property(port->connector);
> > + }
> > +
> > + mgr->cbs->register_connector(port->connector);
> > + return;
> > +
> > +error:
> > + DRM_ERROR("Failed to create connector for port %p: %d\n", port, ret);
> > +}
> > +
> > static void
> > drm_dp_mst_handle_link_address_port(struct drm_dp_mst_branch *mstb,
> > struct drm_device *dev,
> > @@ -1913,8 +1944,12 @@ drm_dp_mst_handle_link_address_port(struct
> > drm_dp_mst_branch *mstb,
> > {
> > struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;
> > struct drm_dp_mst_port *port;
> > - bool created = false;
> > - int old_ddps = 0;
> > + struct drm_dp_mst_branch *child_mstb = NULL;
> > + struct drm_connector *connector_to_destroy = NULL;
> > + int old_ddps = 0, ret;
> > + u8 new_pdt = DP_PEER_DEVICE_NONE;
> > + bool created = false, send_link_addr = false,
> > + create_connector = false;
> >
> > port = drm_dp_get_port(mstb, port_msg->port_number);
> > if (!port) {
> > @@ -1923,6 +1958,7 @@ drm_dp_mst_handle_link_address_port(struct
> > drm_dp_mst_branch *mstb,
> > return;
> > kref_init(&port->topology_kref);
> > kref_init(&port->malloc_kref);
> > + mutex_init(&port->lock);
> > port->parent = mstb;
> > port->port_num = port_msg->port_number;
> > port->mgr = mgr;
> > @@ -1937,11 +1973,17 @@ drm_dp_mst_handle_link_address_port(struct
> > drm_dp_mst_branch *mstb,
> > drm_dp_mst_get_mstb_malloc(mstb);
> >
> > created = true;
> > - } else {
> > - old_ddps = port->ddps;
> > }
> >
> > + mutex_lock(&port->lock);
> > + drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
> > +
> > + if (!created)
> > + old_ddps = port->ddps;
> > +
> > port->input = port_msg->input_port;
> > + if (!port->input)
> > + new_pdt = port_msg->peer_device_type;
> > port->mcs = port_msg->mcs;
> > port->ddps = port_msg->ddps;
> > port->ldps = port_msg->legacy_device_plug_status;
> > @@ -1969,44 +2011,58 @@ drm_dp_mst_handle_link_address_port(struct
> > drm_dp_mst_branch *mstb,
> > }
> > }
> >
> > - if (!port->input) {
> > - int ret = drm_dp_port_set_pdt(port,
> > - port_msg->peer_device_type);
> > - if (ret == 1) {
> > - drm_dp_send_link_address(mgr, port->mstb);
> > - } else if (ret < 0) {
> > - DRM_ERROR("Failed to change PDT on port %p: %d\n",
> > - port, ret);
> > - goto fail;
> > + ret = drm_dp_port_set_pdt(port, new_pdt);
> > + if (ret == 1) {
> > + send_link_addr = true;
> > + } else if (ret < 0) {
> > + DRM_ERROR("Failed to change PDT on port %p: %d\n",
> > + port, ret);
> > + goto fail_unlock;
> > + }
> > +
> > + if (send_link_addr) {
> > + mutex_lock(&mgr->lock);
> > + if (port->mstb) {
> > + child_mstb = port->mstb;
> > + drm_dp_mst_get_mstb_malloc(child_mstb);
> > }
> > + mutex_unlock(&mgr->lock);
> > }
> >
> > - if (created && !port->input) {
> > - char proppath[255];
> > + /*
> > + * We unset port->connector before dropping connection_mutex so that
> > + * there's no chance any of the atomic MST helpers can accidentally
> > + * associate a to-be-destroyed connector with a port.
> > + */
> > + if (port->connector && port->input) {
> > + connector_to_destroy = port->connector;
> > + port->connector = NULL;
> > + } else if (!port->connector && !port->input) {
> > + create_connector = true;
> > + }
> >
> > - build_mst_prop_path(mstb, port->port_num, proppath,
> > - sizeof(proppath));
> > - port->connector = (*mgr->cbs->add_connector)(mgr, port,
> > - proppath);
> > - if (!port->connector)
> > - goto fail;
> > + drm_modeset_unlock(&dev->mode_config.connection_mutex);
>
> Do you drop this early b/c it deadlocks with something upstack? If so, I
> wonder if you could plumb an acquire context through the appropriate
> functions to avoid needing the port->lock at all?

I'll give this a shot, as it would definitely be nicer then having port->lock
>
> Sean
>
> >
> > - if ((port->pdt == DP_PEER_DEVICE_DP_LEGACY_CONV ||
> > - port->pdt == DP_PEER_DEVICE_SST_SINK) &&
> > - port->port_num >= DP_MST_LOGICAL_PORT_0) {
> > - port->cached_edid = drm_get_edid(port->connector,
> > - &port->aux.ddc);
> > - drm_connector_set_tile_property(port->connector);
> > - }
> > + if (connector_to_destroy)
> > + mgr->cbs->destroy_connector(mgr, connector_to_destroy);
> > + else if (create_connector)
> > + drm_dp_mst_port_add_connector(mstb, port);
> > +
> > + mutex_unlock(&port->lock);
> >
> > - (*mgr->cbs->register_connector)(port->connector);
> > + if (send_link_addr && child_mstb) {
> > + drm_dp_send_link_address(mgr, child_mstb);
> > + drm_dp_mst_put_mstb_malloc(child_mstb);
> > }
> >
> > /* put reference to this port */
> > drm_dp_mst_topology_put_port(port);
> > return;
> >
> > -fail:
> > +fail_unlock:
> > + drm_modeset_unlock(&dev->mode_config.connection_mutex);
> > + mutex_unlock(&port->lock);
> > +
> > /* Remove it from the port list */
> > mutex_lock(&mgr->lock);
> > list_del(&port->next);
> > @@ -2022,6 +2078,7 @@ static void
> > drm_dp_mst_handle_conn_stat(struct drm_dp_mst_branch *mstb,
> > struct drm_dp_connection_status_notify *conn_stat)
> > {
> > + struct drm_device *dev = mstb->mgr->dev;
> > struct drm_dp_mst_port *port;
> > int old_ddps;
> > bool dowork = false;
> > @@ -2030,6 +2087,8 @@ drm_dp_mst_handle_conn_stat(struct drm_dp_mst_branch
> > *mstb,
> > if (!port)
> > return;
> >
> > + drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
> > +
> > old_ddps = port->ddps;
> > port->mcs = conn_stat->message_capability_status;
> > port->ldps = conn_stat->legacy_device_plug_status;
> > @@ -2055,6 +2114,7 @@ drm_dp_mst_handle_conn_stat(struct drm_dp_mst_branch
> > *mstb,
> > }
> > }
> >
> > + drm_modeset_unlock(&dev->mode_config.connection_mutex);
> > drm_dp_mst_topology_put_port(port);
> > if (dowork)
> > queue_work(system_long_wq, &mstb->mgr->work);
> > @@ -2147,28 +2207,34 @@ drm_dp_get_mst_branch_device_by_guid(struct
> > drm_dp_mst_topology_mgr *mgr,
> > static void drm_dp_check_and_send_link_address(struct
> > drm_dp_mst_topology_mgr *mgr,
> > struct drm_dp_mst_branch *mstb)
> > {
> > + struct drm_device *dev = mgr->dev;
> > 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);
> >
> > list_for_each_entry(port, &mstb->ports, next) {
> > - if (port->input)
> > - continue;
> > + struct drm_dp_mst_branch *mstb_child = NULL;
> > +
> > + drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
> >
> > - if (!port->ddps)
> > + if (port->input || !port->ddps) {
> > + drm_modeset_unlock(&dev-
> > >mode_config.connection_mutex);
> > continue;
> > + }
> >
> > if (!port->available_pbn)
> > drm_dp_send_enum_path_resources(mgr, mstb, port);
> >
> > - if (port->mstb) {
> > + if (port->mstb)
> > mstb_child = drm_dp_mst_topology_get_mstb_validated(
> > mgr, port->mstb);
> > - if (mstb_child) {
> > - drm_dp_check_and_send_link_address(mgr,
> > mstb_child);
> > - drm_dp_mst_topology_put_mstb(mstb_child);
> > - }
> > +
> > + drm_modeset_unlock(&dev->mode_config.connection_mutex);
> > +
> > + if (mstb_child) {
> > + drm_dp_check_and_send_link_address(mgr, mstb_child);
> > + drm_dp_mst_topology_put_mstb(mstb_child);
> > }
> > }
> > }
> > diff --git a/include/drm/drm_dp_mst_helper.h
> > b/include/drm/drm_dp_mst_helper.h
> > index 7d80c38ee00e..1efbb086f7ac 100644
> > --- a/include/drm/drm_dp_mst_helper.h
> > +++ b/include/drm/drm_dp_mst_helper.h
> > @@ -45,23 +45,34 @@ struct drm_dp_vcpi {
> > /**
> > * struct drm_dp_mst_port - MST port
> > * @port_num: port number
> > - * @input: if this port is an input port.
> > - * @mcs: message capability status - DP 1.2 spec.
> > - * @ddps: DisplayPort Device Plug Status - DP 1.2
> > - * @pdt: Peer Device Type
> > - * @ldps: Legacy Device Plug Status
> > - * @dpcd_rev: DPCD revision of device on this port
> > - * @num_sdp_streams: Number of simultaneous streams
> > - * @num_sdp_stream_sinks: Number of stream sinks
> > - * @available_pbn: Available bandwidth for this port.
> > + * @input: if this port is an input port. Protected by
> > + * &drm_device.mode_config.connection_mutex.
> > + * @mcs: message capability status - DP 1.2 spec. Protected by
> > + * &drm_device.mode_config.connection_mutex.
> > + * @ddps: DisplayPort Device Plug Status - DP 1.2. Protected by
> > + * &drm_device.mode_config.connection_mutex.
> > + * @pdt: Peer Device Type. Protected by
> > + * &drm_device.mode_config.connection_mutex.
> > + * @ldps: Legacy Device Plug Status. Protected by
> > + * &drm_device.mode_config.connection_mutex.
> > + * @dpcd_rev: DPCD revision of device on this port. Protected by
> > + * &drm_device.mode_config.connection_mutex.
> > + * @num_sdp_streams: Number of simultaneous streams. Protected by
> > + * &drm_device.mode_config.connection_mutex.
> > + * @num_sdp_stream_sinks: Number of stream sinks. Protected by
> > + * &drm_device.mode_config.connection_mutex.
> > + * @available_pbn: Available bandwidth for this port. Protected by
> > + * &drm_device.mode_config.connection_mutex.
> > * @next: link to next port on this branch device
> > * @mstb: branch device on this port, protected by
> > * &drm_dp_mst_topology_mgr.lock
> > * @aux: i2c aux transport to talk to device connected to this port,
> > protected
> > - * by &drm_dp_mst_topology_mgr.lock
> > + * by &drm_device.mode_config.connection_mutex.
> > * @parent: branch device parent of this port
> > * @vcpi: Virtual Channel Payload info for this port.
> > - * @connector: DRM connector this port is connected to.
> > + * @connector: DRM connector this port is connected to. Protected by
> > @lock.
> > + * When there is already a connector registered for this port, this is
> > also
> > + * protected by &drm_device.mode_config.connection_mutex.
> > * @mgr: topology manager this port lives under.
> > *
> > * This structure represents an MST port endpoint on a device somewhere
> > @@ -100,6 +111,12 @@ struct drm_dp_mst_port {
> > struct drm_connector *connector;
> > struct drm_dp_mst_topology_mgr *mgr;
> >
> > + /**
> > + * @lock: Protects @connector. If needed, this lock should be grabbed
> > + * before &drm_device.mode_config.connection_mutex.
> > + */
> > + struct mutex lock;
> > +
> > /**
> > * @cached_edid: for DP logical ports - make tiling work by ensuring
> > * that the EDID for all connectors is read immediately.
> > --
> > 2.21.0
> >
--
Cheers,
Lyude Paul