title: How to handle git bisect with external code causing failure
body: <p>I am having an issue where a code change between two versions of the linux kernel is causing an issue. While using <code>git bisect</code>, I find that I can't narrow down the original problem because of an unrelated problem in the linux kernel (graphics corruption) that makes it impossible to track down the original issue.</p>
  
  <p>With <code>git bisect</code>, there are two choices: good or bad; and in this case I can't mark the patch 'good' because of the unrelated issue.  </p>
  
  <p>Do I mark that patch 'bad' according to git bisect or do I do something else?</p>