Fix and improve chunkDesc locking
Fix and improve chunkDesc locking

tomwilkie/prometheus,dsymonds/prometheus,GoogleCloudPlatform/prometheus,tattsun/prometheus,amorken/prometheus,tattsun/prometheus,dsymonds/prometheus,SaltedMan/prometheus-annotated,keegancsmith/prometheus,sudhi-vm/prometheus,agaoglu/prometheus,gottwald/prometheus,dsymonds/prometheus,GoogleCloudPlatform/prometheus,GoogleCloudPlatform/prometheus,agaoglu/prometheus,prometheus/prometheus,slok/prometheus,alileza/prometheus,sudhi-vm/prometheus,AlekSi/prometheus,tomwilkie/prometheus,Stackdriver/stackdriver-prometheus,amorken/prometheus,brancz/prometheus,prometheus/prometheus,brancz/prometheus,JavierZunzunegui/prometheus,tomwilkie/prometheus,kzittritsch/prometheus,eliothedeman/prometheus,kzittritsch/prometheus,dmilstein/prometheus,tattsun/prometheus,Conorbro/prometheus,msiebuhr/prometheus,Stackdriver/stackdriver-prometheus,Gouthamve/prometheus,prometheus/prometheus,yanghongkjxy/prometheus,tattsun/prometheus,AlekSi/prometheus,Gouthamve/prometheus,Conorbro/prometheus,kangwoo/prometheus,datajet-io/prometheus,msiebuhr/prometheus,dmilstein/prometheus,PrFalken/prometheus,adamron1/prometheus,Gouthamve/prometheus,ton31337/prometheus,gottwald/prometheus,dmilstein/prometheus,gottwald/prometheus,eliothedeman/prometheus,GoogleCloudPlatform/prometheus,JavierZunzunegui/prometheus,brancz/prometheus,PrFalken/prometheus,dsymonds/prometheus,JavierZunzunegui/prometheus,alileza/prometheus,keegancsmith/prometheus,Colstuwjx/prometheus,Gouthamve/prometheus,yanghongkjxy/prometheus,ton31337/prometheus,Stackdriver/stackdriver-prometheus,prometheus/prometheus,AlekSi/prometheus,kangwoo/prometheus,datajet-io/prometheus,agaoglu/prometheus,datajet-io/prometheus,GoogleCloudPlatform/prometheus,eliothedeman/prometheus,Colstuwjx/prometheus,prometheus/prometheus,Conorbro/prometheus,yanghongkjxy/prometheus,sudhi-vm/prometheus,kangwoo/prometheus,ton31337/prometheus,dmilstein/prometheus,PrFalken/prometheus,kzittritsch/prometheus,agaoglu/prometheus,Colstuwjx/prometheus,Stackdriver/stackdriver-prometheus,slok/prometheus,yanghongkjxy/prometheus,eliothedeman/prometheus,alileza/prometheus,amorken/prometheus,amorken/prometheus,SaltedMan/prometheus-annotated,keegancsmith/prometheus,ton31337/prometheus,kangwoo/prometheus,tomwilkie/prometheus,sudhi-vm/prometheus,Conorbro/prometheus,msiebuhr/prometheus,alileza/prometheus,SaltedMan/prometheus-annotated,msiebuhr/prometheus,keegancsmith/prometheus,JavierZunzunegui/prometheus,Colstuwjx/prometheus,SaltedMan/prometheus-annotated,adamron1/prometheus,alileza/prometheus,datajet-io/prometheus,PrFalken/prometheus,slok/prometheus,slok/prometheus,keegancsmith/prometheus,adamron1/prometheus,gottwald/prometheus,adamron1/prometheus,brancz/prometheus,kzittritsch/prometheus,AlekSi/prometheus