drm/i915: don't hang userspace when the gpu reset is stuck

With the gpu reset no longer using a trylock we've increased the
chances of userspace getting stuck quite a bit. To make that
(hopefully) rare case more paletable time out when waiting for the gpu
reset code to complete and signal this little issue to the caller by
returning -EIO.

This should help userspace to somewhat gracefully fall back and
hopefully allow the user to grab some logs and reboot the machine
(instead of staring at a frozen X screen in agony).

Suggested by Chris Wilson because I've been stubborn about allowing
the gpu reset code no to fail, ever (by removing the trylock).

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Tested-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index af6a510..7d28555 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -96,9 +96,18 @@ i915_gem_wait_for_error(struct drm_device *dev)
        if (!atomic_read(&dev_priv->mm.wedged))
                return 0;
 
-       ret = wait_for_completion_interruptible(x);
-       if (ret)
+       /*
+        * Only wait 10 seconds for the gpu reset to complete to avoid hanging
+        * userspace. If it takes that long something really bad is going on and
+        * we should simply try to bail out and fail as gracefully as possible.
+        */
+       ret = wait_for_completion_interruptible_timeout(x, 10*HZ);
+       if (ret == 0) {
+               DRM_ERROR("Timed out waiting for the gpu reset to complete\n");
+               return -EIO;
+       } else if (ret < 0) {
                return ret;
+       }
 
        if (atomic_read(&dev_priv->mm.wedged)) {
                /* GPU is hung, bump the completion count to account for