Btrfs: catch invalid free space trees

commit 6675df311db87aa2107a04ef97e19420953cbace upstream.

There are two separate issues that can lead to corrupted free space
trees.

1. The free space tree bitmaps had an endianness issue on big-endian
   systems which is fixed by an earlier patch in this series.
2. btrfs-progs before v4.7.3 modified filesystems without updating the
   free space tree.

To catch both of these issues at once, we need to force the free space
tree to be rebuilt. To do so, add a FREE_SPACE_TREE_VALID compat_ro bit.
If the bit isn't set, we know that it was either produced by a broken
big-endian kernel or may have been corrupted by btrfs-progs.

This also provides us with a way to add rudimentary read-write support
for the free space tree to btrfs-progs: it can just clear this bit and
have the kernel rebuild the free space tree.

Tested-by: Holger Hoffstätte <holger@applied-asynchrony.com>
Tested-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 72f50480eee7bf837abcfd9a9e3e12521c958ddf..699ee7c45ce40d5081a7f72b379f474f21aa0bb7 100644 (file)
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -265,7 +265,8 @@ struct btrfs_super_block {
 #define BTRFS_FEATURE_COMPAT_SAFE_CLEAR                0ULL
 
 #define BTRFS_FEATURE_COMPAT_RO_SUPP                   \
-       (BTRFS_FEATURE_COMPAT_RO_FREE_SPACE_TREE)
+       (BTRFS_FEATURE_COMPAT_RO_FREE_SPACE_TREE |      \
+        BTRFS_FEATURE_COMPAT_RO_FREE_SPACE_TREE_VALID)
 
 #define BTRFS_FEATURE_COMPAT_RO_SAFE_SET       0ULL
 #define BTRFS_FEATURE_COMPAT_RO_SAFE_CLEAR     0ULL

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 864cf3be025124a9b80344920a8f46181046b552..c14e8c70d26aec720a70a817b4965ce63163c2a6 100644 (file)
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2528,6 +2528,7 @@ int open_ctree(struct super_block *sb,
        int num_backups_tried = 0;
        int backup_index = 0;
        int max_active;
+       int clear_free_space_tree = 0;
 
        tree_root = fs_info->tree_root = btrfs_alloc_root(fs_info, GFP_KERNEL);
        chunk_root = fs_info->chunk_root = btrfs_alloc_root(fs_info, GFP_KERNEL);
@@ -3129,6 +3130,14 @@ retry_root_backup:
 
        if (btrfs_test_opt(tree_root, CLEAR_CACHE) &&
            btrfs_fs_compat_ro(fs_info, FREE_SPACE_TREE)) {
+               clear_free_space_tree = 1;
+       } else if (btrfs_fs_compat_ro(fs_info, FREE_SPACE_TREE) &&
+                  !btrfs_fs_compat_ro(fs_info, FREE_SPACE_TREE_VALID)) {
+               btrfs_warn(fs_info, "free space tree is invalid");
+               clear_free_space_tree = 1;
+       }
+
+       if (clear_free_space_tree) {
                btrfs_info(fs_info, "clearing free space tree");
                ret = btrfs_clear_free_space_tree(fs_info);
                if (ret) {

diff --git a/fs/btrfs/free-space-tree.c b/fs/btrfs/free-space-tree.c
index 68ce45a2b763d2f435e47d456334cc80296bbf35..0e041bf75c713abdd64673da732c49ead035d02c 100644 (file)
--- a/fs/btrfs/free-space-tree.c
+++ b/fs/btrfs/free-space-tree.c
@@ -1182,6 +1182,7 @@ int btrfs_create_free_space_tree(struct btrfs_fs_info *fs_info)
        }
 
        btrfs_set_fs_compat_ro(fs_info, FREE_SPACE_TREE);
+       btrfs_set_fs_compat_ro(fs_info, FREE_SPACE_TREE_VALID);
        fs_info->creating_free_space_tree = 0;
 
        ret = btrfs_commit_transaction(trans, tree_root);
@@ -1250,6 +1251,7 @@ int btrfs_clear_free_space_tree(struct btrfs_fs_info *fs_info)
                return PTR_ERR(trans);
 
        btrfs_clear_fs_compat_ro(fs_info, FREE_SPACE_TREE);
+       btrfs_clear_fs_compat_ro(fs_info, FREE_SPACE_TREE_VALID);
        fs_info->free_space_root = NULL;
 
        ret = clear_free_space_tree(trans, free_space_root);

diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index 2bdd1e3e70076dd3476e3398452c4837b2b80f9b..409be3555a3e4431e450d32287748f6efd1915e6 100644 (file)
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -239,7 +239,17 @@ struct btrfs_ioctl_fs_info_args {
  * Used by:
  * struct btrfs_ioctl_feature_flags
  */
-#define BTRFS_FEATURE_COMPAT_RO_FREE_SPACE_TREE        (1ULL << 0)
+#define BTRFS_FEATURE_COMPAT_RO_FREE_SPACE_TREE                (1ULL << 0)
+/*
+ * Older kernels (< 4.9) on big-endian systems produced broken free space tree
+ * bitmaps, and btrfs-progs also used to corrupt the free space tree (versions
+ * < 4.7.3).  If this bit is clear, then the free space tree cannot be trusted.
+ * btrfs-progs can also intentionally clear this bit to ask the kernel to
+ * rebuild the free space tree, however this might not work on older kernels
+ * that do not know about this bit. If not sure, clear the cache manually on
+ * first mount when booting older kernel versions.
+ */
+#define BTRFS_FEATURE_COMPAT_RO_FREE_SPACE_TREE_VALID  (1ULL << 1)
 
 #define BTRFS_FEATURE_INCOMPAT_MIXED_BACKREF   (1ULL << 0)
 #define BTRFS_FEATURE_INCOMPAT_DEFAULT_SUBVOL  (1ULL << 1)