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

Greg Kroah-Hartman
2022-06-27T11:36:25Z

From: Qu Wenruo <wqu@suse.com>

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@vger.kernel.org # 5.15+
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
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);