linux-kernel - [PATCH 5.15 033/121] btrfs: zoned: set pseudo max append zone limit in zone emulation mode

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Date:   Tue, 13 Sep 2022 16:03:44 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Johannes Thumshirn <johannes.thumshirn@....com>,
        Naohiro Aota <naohiro.aota@....com>,
        Shinichiro Kawasaki <shinichiro.kawasaki@....com>,
        David Sterba <dsterba@...e.com>
Subject: [PATCH 5.15 033/121] btrfs: zoned: set pseudo max append zone limit in zone emulation mode

From: Shin'ichiro Kawasaki <shinichiro.kawasaki@....com>

commit cac5c44c48c9fb9cc31bea15ebd9ef0c6462314f upstream.

The commit 7d7672bc5d10 ("btrfs: convert count_max_extents() to use
fs_info->max_extent_size") introduced a division by
fs_info->max_extent_size. This max_extent_size is initialized with max
zone append limit size of the device btrfs runs on. However, in zone
emulation mode, the device is not zoned then its zone append limit is
zero. This resulted in zero value of fs_info->max_extent_size and caused
zero division error.

Fix the error by setting non-zero pseudo value to max append zone limit
in zone emulation mode. Set the pseudo value based on max_segments as
suggested in the commit c2ae7b772ef4 ("btrfs: zoned: revive
max_zone_append_bytes").

Fixes: 7d7672bc5d10 ("btrfs: convert count_max_extents() to use fs_info->max_extent_size")
CC: stable@...r.kernel.org # 5.12+
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@....com>
Reviewed-by: Naohiro Aota <naohiro.aota@....com>
Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@....com>
Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/btrfs/zoned.c |   15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

--- a/fs/btrfs/zoned.c
+++ b/fs/btrfs/zoned.c
@@ -392,10 +392,19 @@ int btrfs_get_dev_zone_info(struct btrfs
 	 * since btrfs adds the pages one by one to a bio, and btrfs cannot
 	 * increase the metadata reservation even if it increases the number of
 	 * extents, it is safe to stick with the limit.
+	 *
+	 * With the zoned emulation, we can have non-zoned device on the zoned
+	 * mode. In this case, we don't have a valid max zone append size. So,
+	 * use max_segments * PAGE_SIZE as the pseudo max_zone_append_size.
 	 */
-	zone_info->max_zone_append_size =
-		min_t(u64, (u64)bdev_max_zone_append_sectors(bdev) << SECTOR_SHIFT,
-		      (u64)bdev_max_segments(bdev) << PAGE_SHIFT);
+	if (bdev_is_zoned(bdev)) {
+		zone_info->max_zone_append_size = min_t(u64,
+			(u64)bdev_max_zone_append_sectors(bdev) << SECTOR_SHIFT,
+			(u64)bdev_max_segments(bdev) << PAGE_SHIFT);
+	} else {
+		zone_info->max_zone_append_size =
+			(u64)bdev_max_segments(bdev) << PAGE_SHIFT;
+	}
 	if (!IS_ALIGNED(nr_sectors, zone_sectors))
 		zone_info->nr_zones++;