drm: Serialise multiple event readers
The previous patch reintroduced a race condition whereby a failure in
one reader may allow a second reader to see out-of-order events.
Introduce a mutex to serialise readers so that an event is completed in
its entirety before another reader may process an event. The two readers
may race against each other, but the events each retrieves are in the
correct order.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Thomas Hellstrom <thellstrom@vmware.com>
Cc: Takashi Iwai <tiwai@suse.de>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1448462343-2072-2-git-send-email-chris@chris-wilson.co.uk
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
index eb8702d..81df9ae 100644
--- a/drivers/gpu/drm/drm_fops.c
+++ b/drivers/gpu/drm/drm_fops.c
@@ -172,6 +172,8 @@
init_waitqueue_head(&priv->event_wait);
priv->event_space = 4096; /* set aside 4k for event buffer */
+ mutex_init(&priv->event_read_lock);
+
if (drm_core_check_feature(dev, DRIVER_GEM))
drm_gem_open(dev, priv);
@@ -483,11 +485,15 @@
{
struct drm_file *file_priv = filp->private_data;
struct drm_device *dev = file_priv->minor->dev;
- ssize_t ret = 0;
+ ssize_t ret;
if (!access_ok(VERIFY_WRITE, buffer, count))
return -EFAULT;
+ ret = mutex_lock_interruptible(&file_priv->event_read_lock);
+ if (ret)
+ return ret;
+
for (;;) {
struct drm_pending_event *e = NULL;
@@ -509,12 +515,13 @@
break;
}
+ mutex_unlock(&file_priv->event_read_lock);
ret = wait_event_interruptible(file_priv->event_wait,
!list_empty(&file_priv->event_list));
- if (ret < 0)
- break;
-
- ret = 0;
+ if (ret >= 0)
+ ret = mutex_lock_interruptible(&file_priv->event_read_lock);
+ if (ret)
+ return ret;
} else {
unsigned length = e->event->length;
@@ -537,6 +544,7 @@
e->destroy(e);
}
}
+ mutex_unlock(&file_priv->event_read_lock);
return ret;
}