[PATCH] drm: Don't block the kworker waiting for mode_config.lock in output_poll()

[Chris Wilson]

If we cannot acquire the mode_config.lock 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 at chris-wilson.co.uk>
---
 drivers/gpu/drm/drm_probe_helper.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
index ff9ba6f35248..0bf629354297 100644
--- a/drivers/gpu/drm/drm_probe_helper.c
+++ b/drivers/gpu/drm/drm_probe_helper.c
@@ -394,7 +394,11 @@ 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. */
-- 
2.11.0