Avoid arena deallocation while uffd-GC is visiting them

Releasing linear-alloc leads to arenas being deallocated. If a GC is
taking place simultaneously, then we may end up visiting an arena which
is already deallocated.

Bug: 160737021
Test: art/test/testrunner/testrunner.py --host --gcstress -t 1003
Change-Id: Ic0621efeb31d13cb2785ab7a4e3c8c67082189b5
3 files changed