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

[ Upstream commit 60b801999c48b6c1dd04e653a38e2e613664264e ]

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
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
index 3f20f598cd7cff6b2d57ea171467bb84bb5885bb..9c5bc0121ff99a0f28282c80254a963b6e46be0b 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;
                        }