If a chroot of a build fails, the entire build is marked as "failed" at the top of the build details page when there is still a chroot in the running state. See attached screenshot for an example. Even though the screenshot does not show a logged in version of the page, the controls at the top of the page list the buttons for a failed build (Delete, or Resubmit). So there is no option ot cancel the build anymore even though it is still techincally running. The build should be in a "running" state until all the chroots are either skipped, failed or success.
Created attachment 995764 [details] screenshot
+1
Another option would be to add another column into the builds overview table, showing the number of still running chroot jobs.
Fixed by b924147b (https://github.com/fedora-copr/copr/commit/b924147bde8a50696be95f7368ac7dbf02dd2cef). Thanks.
Package including this fix has been deployed on production instance of Copr.