[Intel-gfx] [PATCH] drm/probe-helper: don't lose hotplug event
Rob Clark
robdclark at gmail.com
Wed Jan 21 13:40:31 PST 2015
On Wed, Jan 21, 2015 at 9:41 AM, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> There's a race window (small for hpd, 10s large for polled outputs)
> where userspace could sneak in with an unrelated connnector probe
> ioctl call and eat the hotplug event (since neither the hpd nor the
> poll code see a state change).
>
> To avoid this, check whether the connector state changes in all other
> ->detect calls (in the current helper code that's only probe_single)
> and if that's the case, fire off a hotplug event. Note that we can't
> directly call the hotplug event handler, since that expects that no
> locks are held (due to reentrancy with the fb code to update the kms
> console).
>
> Also, this requires that drivers using the probe_single helper
> function set up the poll work. All current drivers do that already,
> and with the reworked hpd handling there'll be no downside to
> unconditionally setting up the poll work any more.
>
> v2: Review from Rob Clark
> - Don't bail out of the output poll work immediately if it's disabled
> to make sure we deliver the delayed hoptplug events. Instead just
> jump to the tail.
> - Don't scheduel the work when it's not set up. Would be a driver bug
> since using probe helpers for anything dynamic without them
> initialized makes them all noops.
>
> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk> (v1)
> Cc: Rob Clark <robdclark at gmail.com>
> Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Reviewed-by: Rob Clark <robdclark at gmail.com>
and with the monitor that started all this, plus the addition of:
http://lists.freedesktop.org/archives/dri-devel/2015-January/075901.html
Tested-by: Rob Clark <robdclark at gmail.com>
> ---
> drivers/gpu/drm/drm_probe_helper.c | 36 ++++++++++++++++++++++++++++++++++--
> include/drm/drm_crtc.h | 1 +
> 2 files changed, 35 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
> index 2fbdcca7ca9a..33bf550a1d3f 100644
> --- a/drivers/gpu/drm/drm_probe_helper.c
> +++ b/drivers/gpu/drm/drm_probe_helper.c
> @@ -103,6 +103,7 @@ static int drm_helper_probe_single_connector_modes_merge_bits(struct drm_connect
> int count = 0;
> int mode_flags = 0;
> bool verbose_prune = true;
> + enum drm_connector_status old_status;
>
> WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
>
> @@ -121,7 +122,33 @@ static int drm_helper_probe_single_connector_modes_merge_bits(struct drm_connect
> if (connector->funcs->force)
> connector->funcs->force(connector);
> } else {
> + old_status = connector->status;
> +
> connector->status = connector->funcs->detect(connector, true);
> +
> + /*
> + * Normally either the driver's hpd code or the poll loop should
> + * pick up any changes and fire the hotplug event. But if
> + * userspace sneaks in a probe, we might miss a change. Hence
> + * check here, and if anything changed start the hotplug code.
> + */
> + if (old_status != connector->status) {
> + DRM_DEBUG_KMS("[CONNECTOR:%d:%s] status updated from %d to %d\n",
> + connector->base.id,
> + connector->name,
> + old_status, connector->status);
> +
> + /*
> + * The hotplug event code might call into the fb
> + * helpers, and so expects that we do not hold any
> + * locks. Fire up the poll struct instead, it will
> + * disable itself again.
> + */
> + dev->mode_config.delayed_event = true;
> + if (dev->mode_config.poll_enabled)
> + schedule_delayed_work(&dev->mode_config.output_poll_work,
> + 0);
> + }
> }
>
> /* Re-enable polling in case the global poll config changed. */
> @@ -274,10 +301,14 @@ static void output_poll_execute(struct work_struct *work)
> struct drm_device *dev = container_of(delayed_work, struct drm_device, mode_config.output_poll_work);
> struct drm_connector *connector;
> enum drm_connector_status old_status;
> - bool repoll = false, changed = false;
> + bool repoll = false, changed;
> +
> + /* Pick up any changes detected by the probe functions. */
> + changed = dev->mode_config.delayed_event;
> + dev->mode_config.delayed_event = false;
>
> if (!drm_kms_helper_poll)
> - return;
> + goto out;
>
> mutex_lock(&dev->mode_config.mutex);
> list_for_each_entry(connector, &dev->mode_config.connector_list, head) {
> @@ -319,6 +350,7 @@ static void output_poll_execute(struct work_struct *work)
>
> mutex_unlock(&dev->mode_config.mutex);
>
> +out:
> if (changed)
> drm_kms_helper_hotplug_event(dev);
>
> diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
> index f444263055c5..65da9fb939a7 100644
> --- a/include/drm/drm_crtc.h
> +++ b/include/drm/drm_crtc.h
> @@ -1089,6 +1089,7 @@ struct drm_mode_config {
> /* output poll support */
> bool poll_enabled;
> bool poll_running;
> + bool delayed_event;
> struct delayed_work output_poll_work;
>
> /* pointers to standard properties */
> --
> 2.1.4
>
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