Add a mutex to protect concurrent access to mountedLayer.references map.
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
(cherry picked from commit f73b5cb4e8b9a23ad6700577840582d66017a733)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
Upstream-commit: bb80a60be2a9236b0db27222310f568e1d3fba11
Component: engine