filesystem softdep_process_worklist() is called in a loop until it indicates
that no dependancies remain, but the determination of that fact depends on
there only being one softdep_process_worklist() instance running. It was
possible for the syncer to also be running softdep_process_worklist()
and the pre-existing checks in the code to prevent this were not sufficient
to prevent the race. This patch solves the problem.
Approved-by: mckusick
f8e071a1eb