drm: Wake up next in drm_read() chain if we are forced to putback the event

After an event is sent, we try to copy it into the user buffer of the
first waiter in drm_read() and if the user buffer doesn't have enough
room we put it back onto the list. However, we didn't wake up any
subsequent waiter, so that event may sit on the list until either a new
vblank event is sent or a new waiter appears. Rare, but in the worst
case may lead to a stuck process.

Testcase: igt/drm_read/short-buffer-wakeup
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170804082328.17173-1-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
index ee4df8f8a62d55fa75c740bb7b3ab307af4e049b..f782d3103d29bb7b1542110a4a6bc2d7db050c87 100644 (file)
--- a/drivers/gpu/drm/drm_file.c
+++ b/drivers/gpu/drm/drm_file.c
@@ -567,6 +567,7 @@ put_back_event:
                                file_priv->event_space -= length;
                                list_add(&e->link, &file_priv->event_list);
                                spin_unlock_irq(&dev->event_lock);
+                               wake_up_interruptible(&file_priv->event_wait);
                                break;
                        }