zram: fix race between zram_reset_device() and disksize_store()

When the ->init_lock is released in zram_reset_device(), disksize_store()
can come in and try to allocate meta, but zram_reset_device() is freeing
free meta, so cause races.

Link: https://lore.kernel.org/linux-block/20210927163805.808907-1-mcgrof@kernel.org/T/#mc617f865a3fa2778e40f317ddf48f6447c20c073


Reported-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Link: https://lore.kernel.org/r/20211025025426.2815424-2-ming.lei@redhat.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>