I had a build of v4.4.24, with CONFIG_NVM not set, fail like this:
drivers/block/null_blk.c:569:27: error: storage size of 'null_lnvm_dev_ops'
static struct nvm_dev_ops null_lnvm_dev_ops;
scripts/Makefile.build:264: recipe for target 'drivers/block/null_blk.o'
make: *** [drivers/block/null_blk.o] Error 1
scripts/Makefile.build:403: recipe for target 'drivers/block' failed
make: *** [drivers/block] Error 2
Makefile:959: recipe for target 'drivers' failed
make: *** [drivers] Error 2
Jens' commit a7fd9a4f3e81 ("lightnvm: ensure that nvm_dev_ops can be
used without CONFIG_NVM") fixed that for me (it did require a small
context change to get it applied to v4.4.24). Does it make sense to add
that commit to the v4.4.y stable tree?