Bug 239100 - r348991 breaks unionfs

[UEMURA Tetsuya]

While upgrading my ports from 12.0-RELEASE to 12-STABLE, I encountered a
lot of Text file busy errors, and almost no ports I could update successfully.

Then I attempted to fix/workaround the issue, and finally I found that
r348991 Switch to use shared vnode locks for text files during image
activation broke my uinonfs, which was the culprit for Text file busy
issue.
https://svnweb.freebsd.org/base?view=revision&revision=348991

I filed the issue in Bugzilla. Someone please look at the issue.
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=239100

P.S. For freebsd-current, r348991 was
MFC r347151,347181,347968,348421,348698,348701 .

-- 
UEMURA, Tetsuya <t_uemura at macome.co.jp>