[PATCH 4/5] brd: fix discard end sector

[Yu Kuai]

From: Yu Kuai <yukuai3@xxxxxxxxxx>

brd_do_discard() just aligned start sector to page, this can only work
if the discard size if at least one page. For example:

blkdiscard /dev/ram0 -o 5120 -l 1024

In this case, size = (1024 - (8192 - 5120)), which is a huge value.

Fix the problem by round_down() the end sector.

Fixes: 9ead7efc6f3f ("brd: implement discard support")
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
 drivers/block/brd.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index 21e841e09a89..bf1e1b2a0d28 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -234,18 +234,21 @@ static void brd_free_one_page(struct rcu_head *head)
 static void brd_do_discard(struct brd_device *brd, sector_t sector, u32 size)
 {
 	sector_t aligned_sector = round_up(sector, PAGE_SECTORS);
+	sector_t aligned_end = round_down(sector + (size >> SECTOR_SHIFT),
+					  PAGE_SECTORS);
 	struct page *page;
 
-	size -= (aligned_sector - sector) * SECTOR_SIZE;
+	if (aligned_end <= aligned_sector)
+		return;
+
 	xa_lock(&brd->brd_pages);
-	while (size >= PAGE_SIZE && aligned_sector < rd_size * 2) {
+	while (aligned_sector < aligned_end && aligned_sector < rd_size * 2) {
 		page = __xa_erase(&brd->brd_pages, aligned_sector >> PAGE_SECTORS_SHIFT);
 		if (page) {
 			call_rcu(&page->rcu_head, brd_free_one_page);
 			brd->brd_nr_pages--;
 		}
 		aligned_sector += PAGE_SECTORS;
-		size -= PAGE_SIZE;
 	}
 	xa_unlock(&brd->brd_pages);
 }
-- 
2.39.2