static ssize_t writeback_store()

in zram/zram_drv.c [650:814]

• 124 lines of code
• 29 McCabe index (conditional complexity)

static ssize_t writeback_store(struct device *dev,
		struct device_attribute *attr, const char *buf, size_t len)
{
	struct zram *zram = dev_to_zram(dev);
	unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
	unsigned long index = 0;
	struct bio bio;
	struct bio_vec bio_vec;
	struct page *page;
	ssize_t ret = len;
	int mode, err;
	unsigned long blk_idx = 0;

	if (sysfs_streq(buf, "idle"))
		mode = IDLE_WRITEBACK;
	else if (sysfs_streq(buf, "huge"))
		mode = HUGE_WRITEBACK;
	else {
		if (strncmp(buf, PAGE_WB_SIG, sizeof(PAGE_WB_SIG) - 1))
			return -EINVAL;

		if (kstrtol(buf + sizeof(PAGE_WB_SIG) - 1, 10, &index) ||
				index >= nr_pages)
			return -EINVAL;

		nr_pages = 1;
		mode = PAGE_WRITEBACK;
	}

	down_read(&zram->init_lock);
	if (!init_done(zram)) {
		ret = -EINVAL;
		goto release_init_lock;
	}

	if (!zram->backing_dev) {
		ret = -ENODEV;
		goto release_init_lock;
	}

	page = alloc_page(GFP_KERNEL);
	if (!page) {
		ret = -ENOMEM;
		goto release_init_lock;
	}

	for (; nr_pages != 0; index++, nr_pages--) {
		struct bio_vec bvec;

		bvec.bv_page = page;
		bvec.bv_len = PAGE_SIZE;
		bvec.bv_offset = 0;

		spin_lock(&zram->wb_limit_lock);
		if (zram->wb_limit_enable && !zram->bd_wb_limit) {
			spin_unlock(&zram->wb_limit_lock);
			ret = -EIO;
			break;
		}
		spin_unlock(&zram->wb_limit_lock);

		if (!blk_idx) {
			blk_idx = alloc_block_bdev(zram);
			if (!blk_idx) {
				ret = -ENOSPC;
				break;
			}
		}

		zram_slot_lock(zram, index);
		if (!zram_allocated(zram, index))
			goto next;

		if (zram_test_flag(zram, index, ZRAM_WB) ||
				zram_test_flag(zram, index, ZRAM_SAME) ||
				zram_test_flag(zram, index, ZRAM_UNDER_WB))
			goto next;

		if (mode == IDLE_WRITEBACK &&
			  !zram_test_flag(zram, index, ZRAM_IDLE))
			goto next;
		if (mode == HUGE_WRITEBACK &&
			  !zram_test_flag(zram, index, ZRAM_HUGE))
			goto next;
		/*
		 * Clearing ZRAM_UNDER_WB is duty of caller.
		 * IOW, zram_free_page never clear it.
		 */
		zram_set_flag(zram, index, ZRAM_UNDER_WB);
		/* Need for hugepage writeback racing */
		zram_set_flag(zram, index, ZRAM_IDLE);
		zram_slot_unlock(zram, index);
		if (zram_bvec_read(zram, &bvec, index, 0, NULL)) {
			zram_slot_lock(zram, index);
			zram_clear_flag(zram, index, ZRAM_UNDER_WB);
			zram_clear_flag(zram, index, ZRAM_IDLE);
			zram_slot_unlock(zram, index);
			continue;
		}

		bio_init(&bio, &bio_vec, 1);
		bio_set_dev(&bio, zram->bdev);
		bio.bi_iter.bi_sector = blk_idx * (PAGE_SIZE >> 9);
		bio.bi_opf = REQ_OP_WRITE | REQ_SYNC;

		bio_add_page(&bio, bvec.bv_page, bvec.bv_len,
				bvec.bv_offset);
		/*
		 * XXX: A single page IO would be inefficient for write
		 * but it would be not bad as starter.
		 */
		err = submit_bio_wait(&bio);
		if (err) {
			zram_slot_lock(zram, index);
			zram_clear_flag(zram, index, ZRAM_UNDER_WB);
			zram_clear_flag(zram, index, ZRAM_IDLE);
			zram_slot_unlock(zram, index);
			/*
			 * Return last IO error unless every IO were
			 * not suceeded.
			 */
			ret = err;
			continue;
		}

		atomic64_inc(&zram->stats.bd_writes);
		/*
		 * We released zram_slot_lock so need to check if the slot was
		 * changed. If there is freeing for the slot, we can catch it
		 * easily by zram_allocated.
		 * A subtle case is the slot is freed/reallocated/marked as
		 * ZRAM_IDLE again. To close the race, idle_store doesn't
		 * mark ZRAM_IDLE once it found the slot was ZRAM_UNDER_WB.
		 * Thus, we could close the race by checking ZRAM_IDLE bit.
		 */
		zram_slot_lock(zram, index);
		if (!zram_allocated(zram, index) ||
			  !zram_test_flag(zram, index, ZRAM_IDLE)) {
			zram_clear_flag(zram, index, ZRAM_UNDER_WB);
			zram_clear_flag(zram, index, ZRAM_IDLE);
			goto next;
		}

		zram_free_page(zram, index);
		zram_clear_flag(zram, index, ZRAM_UNDER_WB);
		zram_set_flag(zram, index, ZRAM_WB);
		zram_set_element(zram, index, blk_idx);
		blk_idx = 0;
		atomic64_inc(&zram->stats.pages_stored);
		spin_lock(&zram->wb_limit_lock);
		if (zram->wb_limit_enable && zram->bd_wb_limit > 0)
			zram->bd_wb_limit -=  1UL << (PAGE_SHIFT - 12);
		spin_unlock(&zram->wb_limit_lock);
next:
		zram_slot_unlock(zram, index);
	}

	if (blk_idx)
		free_block_bdev(zram, blk_idx);
	__free_page(page);
release_init_lock:
	up_read(&zram->init_lock);

	return ret;
}