Currently there are two corner cases not handling compat RO flags correctly:

- Remount We can still mount the fs RO with compat RO flags, then remount it RW. We should not allow any write into a fs with unsupported RO flags.

- Still try to search block group items In fact, behavior/on-disk format change to extent tree should not need a full incompat flag.

And since we can ensure fs with unsupported RO flags never got any writes (with above case fixed), then we can even skip block group items search at mount time.

This patch will enhance the unsupported RO compat flags by:

- Reject RW remount if there is unsupported RO compat flags

- Go dummy block group items directly for unsupported RO compat flags In fact, only changes to chunk/subvolume/root/csum trees should go incompat flags.

The latter part should allow future change to extent tree to be compat RO flags.

Thus this patch also needs to be backported to all stable trees.

Cc: stable@vger.kernel.org Signed-off-by: Qu Wenruo wqu@suse.com --- fs/btrfs/block-group.c | 11 ++++++++++- fs/btrfs/super.c | 9 +++++++++ 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c index 38a740d5297c..4a78136bcd17 100644 --- a/fs/btrfs/block-group.c +++ b/fs/btrfs/block-group.c @@ -2186,7 +2186,16 @@ int btrfs_read_block_groups(struct btrfs_fs_info *info) int need_clear = 0; u64 cache_gen;

- if (!root) + /* + * Either no extent root (with ibadroots rescue option) or we have + * unsupporter RO options. The fs can never be mounted RW, so no + * need to waste time search block group items. + * + * This also allows new extent tree related changes to be RO compat, + * no need for a full incompat flag. + */ + if (!root || (btrfs_super_compat_ro_flags(info->super_copy) & + ~BTRFS_FEATURE_COMPAT_RO_SUPP)) return fill_dummy_bgs(info);

key.objectid = 0; diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c index 4c7089b1681b..7d3213e67fb5 100644 --- a/fs/btrfs/super.c +++ b/fs/btrfs/super.c @@ -2110,6 +2110,15 @@ static int btrfs_remount(struct super_block *sb, int *flags, char *data) ret = -EINVAL; goto restore; } + if (btrfs_super_compat_ro_flags(fs_info->super_copy) & + ~BTRFS_FEATURE_COMPAT_RO_SUPP) { + btrfs_err(fs_info, + "can not remount read-write due to unsupported optional flags 0x%llx", + btrfs_super_compat_ro_flags(fs_info->super_copy) & + ~BTRFS_FEATURE_COMPAT_RO_SUPP); + ret = -EINVAL; + goto restore; + } if (fs_info->fs_devices->rw_devices == 0) { ret = -EACCES; goto restore;