Pull md bugfixes from Neil Brown:
"Assorted md bug-fixes for 3.12.
All tagged for -stable releases too"
* tag 'md/3.12-fixes' of git://neil.brown.name/md:
raid5: avoid finding "discard" stripe
raid5: set bio bi_vcnt 0 for discard request
md: avoid deadlock when md_set_badblocks.
md: Fix skipping recovery for read-only arrays.