[PATCH 5.15 015/135] btrfs: prevent remounting to v1 space cache for subpage mount

[Greg Kroah-Hartman]

From: Qu Wenruo <wqu@xxxxxxxx>

commit 0591f04036218d572d54349ea8c7914ad9c82b2b upstream.

Upstream commit 9f73f1aef98b ("btrfs: force v2 space cache usage for
subpage mount") forces subpage mount to use v2 cache, to avoid
deprecated v1 cache which doesn't support subpage properly.

But there is a loophole that user can still remount to v1 cache.

The existing check will only give users a warning, but does not really
prevent to do the remount.

Although remounting to v1 will not cause any problems since the v1 cache
will always be marked invalid when mounted with a different page size,
it's still better to prevent v1 cache at all for subpage mounts.

Fixes: 9f73f1aef98b ("btrfs: force v2 space cache usage for subpage mount")
CC: stable@xxxxxxxxxxxxxxx # 5.15+
Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/btrfs/super.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1917,6 +1917,14 @@ static int btrfs_remount(struct super_bl
 	if (ret)
 		goto restore;
 
+	/* V1 cache is not supported for subpage mount. */
+	if (fs_info->sectorsize < PAGE_SIZE && btrfs_test_opt(fs_info, SPACE_CACHE)) {
+		btrfs_warn(fs_info,
+	"v1 space cache is not supported for page size %lu with sectorsize %u",
+			   PAGE_SIZE, fs_info->sectorsize);
+		ret = -EINVAL;
+		goto restore;
+	}
 	btrfs_remount_begin(fs_info, old_opts, *flags);
 	btrfs_resize_thread_pool(fs_info,
 		fs_info->thread_pool_size, old_thread_pool_size);