[Bug 100727] [skl] [drm] BUG: unable to handle kernel NULL pointer dereference at (null) [drm_kms_helper]

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=100727

--- Comment #16 from Jiri Slaby <jirislaby at gmail.com> ---
I hit it with 4.15.14 right now. I don't know how to reproduce though. 

What about this (mgr->mst_primary seems to be NULL here)?
@@ -1288,7 +1288,10 @@ static struct drm_dp_mst_branch
*drm_dp_get_mst_branch_device(struct drm_dp_mst_
                        }
                }
        }
-       kref_get(&mstb->kref);
+       if (WARN_ON_ONCE(!mstb))
+               ;
+       else
+               kref_get(&mstb->kref);
 out:
        mutex_unlock(&mgr->lock);
        return mstb;

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