drm: Don't block the kworker waiting for mode_config.mutex in output_poll()

If we cannot acquire the mode_config.mutex immediately, just back off and
queue a new attempt after the poll interval. This is mostly to stop the
hung task spam when the system is deadlocked, but it will also lessen
the load (in such extreme cases).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>
[danvet:s/lock/mutex/ per Eric's comment.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20161206113715.30382-1-chris@chris-wilson.co.uk

1 files changed, 5 insertions, 1 deletions

diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
index 078d9703a4fe..ac953f037be7 100644
--- a/drivers/gpu/drm/drm_probe_helper.c
+++ b/drivers/gpu/drm/drm_probe_helper.c
@@ -392,7 +392,11 @@ static void output_poll_execute(struct work_struct *work)
         if (!drm_kms_helper_poll)
                 goto out;
 
-        mutex_lock(&dev->mode_config.mutex);
+        if (!mutex_trylock(&dev->mode_config.mutex)) {
+                repoll = true;
+                goto out;
+        }
+
         drm_for_each_connector(connector, dev) {
 
                 /* Ignore forced connectors. */