BCACHE_DEV_CLOSING
if (test_bit(BCACHE_DEV_CLOSING, &dc->disk.flags))
if (!dc || test_bit(BCACHE_DEV_CLOSING, &dc->disk.flags))
if (test_bit(BCACHE_DEV_CLOSING, &d->flags))
if (!test_and_set_bit(BCACHE_DEV_CLOSING, &d->flags))