drm: Allow determining if current task is output poll worker

commit 25c058ccaf2ebbc3e250ec1e199e161f91fe27d4 upstream.

Introduce a helper to determine if the current task is an output poll
worker.

This allows us to fix a long-standing deadlock in several DRM drivers
wherein the ->runtime_suspend callback waits for the output poll worker
to finish and the worker in turn calls a ->detect callback which waits
for runtime suspend to finish.  The ->detect callback is invoked from
multiple call sites and waiting for runtime suspend to finish is the
correct thing to do except if it's executing in the context of the
worker.

v2: Expand kerneldoc to specifically mention deadlock between
    output poll worker and autosuspend worker as use case. (Lyude)

Cc: Dave Airlie <airlied@redhat.com>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Link: https://patchwork.freedesktop.org/patch/msgid/3549ce32e7f1467102e70d3e9cbf70c46bfe108e.1518593424.git.lukas@wunner.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
index 904966cde32b51886fc5ee9e876a1d2ec992745b..d29fd8443fedaf710c476f01f4fd08ec515cd681 100644 (file)
--- a/drivers/gpu/drm/drm_probe_helper.c
+++ b/drivers/gpu/drm/drm_probe_helper.c
@@ -671,6 +671,26 @@ out:
                schedule_delayed_work(delayed_work, DRM_OUTPUT_POLL_PERIOD);
 }
 
+/**
+ * drm_kms_helper_is_poll_worker - is %current task an output poll worker?
+ *
+ * Determine if %current task is an output poll worker.  This can be used
+ * to select distinct code paths for output polling versus other contexts.
+ *
+ * One use case is to avoid a deadlock between the output poll worker and
+ * the autosuspend worker wherein the latter waits for polling to finish
+ * upon calling drm_kms_helper_poll_disable(), while the former waits for
+ * runtime suspend to finish upon calling pm_runtime_get_sync() in a
+ * connector ->detect hook.
+ */
+bool drm_kms_helper_is_poll_worker(void)
+{
+       struct work_struct *work = current_work();
+
+       return work && work->func == output_poll_execute;
+}
+EXPORT_SYMBOL(drm_kms_helper_is_poll_worker);
+
 /**
  * drm_kms_helper_poll_disable - disable output polling
  * @dev: drm_device

diff --git a/include/drm/drm_crtc_helper.h b/include/drm/drm_crtc_helper.h
index 76e237bd989bef2f81142ef143960d9720651827..6914633037a5359f1355a15e94163dbde7d4ebe2 100644 (file)
--- a/include/drm/drm_crtc_helper.h
+++ b/include/drm/drm_crtc_helper.h
@@ -77,5 +77,6 @@ void drm_kms_helper_hotplug_event(struct drm_device *dev);
 
 void drm_kms_helper_poll_disable(struct drm_device *dev);
 void drm_kms_helper_poll_enable(struct drm_device *dev);
+bool drm_kms_helper_is_poll_worker(void);
 
 #endif