block,btrfs: fix frozen-superblock strand on device add/remove/replace#967

blktests-ci[bot] wants to merge 6 commits into

linus-master_baselinux-blktests/linux-block:linus-master_basefrom

series/1111715=>linus-masterlinux-blktests/linux-block:series/1111715=>linus-masterCopy head branch name to clipboard