[PATCH] block: Discard page cache of zone reset target range

[Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>]

When zone reset ioctl and data read race for a same zone on zoned block
devices, the data read leaves stale page cache even though the zone
reset ioctl zero clears all the zone data on the device. To avoid
non-zero data read from the stale page cache after zone reset, discard
page cache of reset target zones. In same manner as fallocate, call the
function truncate_bdev_range() in blkdev_zone_mgmt_ioctl() before and
after zone reset to ensure the page cache discarded.

This patch can be applied back to the stable kernel version v5.10.y.
Rework is needed for older stable kernels.

Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Fixes: 3ed05a987e0f ("blk-zoned: implement ioctls")
Cc: <stable@vger.kernel.org> # 5.10+
---
 block/blk-zoned.c | 30 ++++++++++++++++++++++++++++--
 1 file changed, 28 insertions(+), 2 deletions(-)

diff --git a/block/blk-zoned.c b/block/blk-zoned.c
index 833978c02e60..990a36be2927 100644
--- a/block/blk-zoned.c
+++ b/block/blk-zoned.c
@@ -329,6 +329,9 @@ int blkdev_zone_mgmt_ioctl(struct block_device *bdev, fmode_t mode,
 	struct request_queue *q;
 	struct blk_zone_range zrange;
 	enum req_opf op;
+	sector_t capacity;
+	loff_t start, end;
+	int ret;
 
 	if (!argp)
 		return -EINVAL;
@@ -349,9 +352,22 @@ int blkdev_zone_mgmt_ioctl(struct block_device *bdev, fmode_t mode,
 	if (copy_from_user(&zrange, argp, sizeof(struct blk_zone_range)))
 		return -EFAULT;
 
+	capacity = get_capacity(bdev->bd_disk);
+	if (zrange.sector + zrange.nr_sectors <= zrange.sector ||
+	    zrange.sector + zrange.nr_sectors > capacity)
+		/* Out of range */
+		return -EINVAL;
+
+	start = zrange.sector << SECTOR_SHIFT;
+	end = ((zrange.sector + zrange.nr_sectors) << SECTOR_SHIFT) - 1;
+
 	switch (cmd) {
 	case BLKRESETZONE:
 		op = REQ_OP_ZONE_RESET;
+		/* Invalidate the page cache, including dirty pages. */
+		ret = truncate_bdev_range(bdev, mode, start, end);
+		if (ret)
+			return ret;
 		break;
 	case BLKOPENZONE:
 		op = REQ_OP_ZONE_OPEN;
@@ -366,8 +382,18 @@ int blkdev_zone_mgmt_ioctl(struct block_device *bdev, fmode_t mode,
 		return -ENOTTY;
 	}
 
-	return blkdev_zone_mgmt(bdev, op, zrange.sector, zrange.nr_sectors,
-				GFP_KERNEL);
+	ret = blkdev_zone_mgmt(bdev, op, zrange.sector, zrange.nr_sectors,
+			       GFP_KERNEL);
+
+	/*
+	 * Invalidate the page cache again for zone reset; if someone wandered
+	 * in and dirtied a page, we just discard it - userspace has no way of
+	 * knowing whether the write happened before or after reset completing.
+	 */
+	if (!ret && cmd == BLKRESETZONE)
+		ret = truncate_bdev_range(bdev, mode, start, end);
+
+	return ret;
 }
 
 static inline unsigned long *blk_alloc_zone_bitmap(int node,
-- 
2.29.2