Btrfs: Properly find the root for snapshotted blocks during chunk relocation

Signed-off-by: Chris Mason <chris.mason@oracle.com>

3 files changed, 156 insertions, 12 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 33ab165591c5..f4b4677bec77 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1459,6 +1459,8 @@ int btrfs_update_root(struct btrfs_trans_handle *trans, struct btrfs_root
                       *item);
 int btrfs_find_last_root(struct btrfs_root *root, u64 objectid, struct
                          btrfs_root_item *item, struct btrfs_key *key);
+int btrfs_search_root(struct btrfs_root *root, u64 search_start,
+                      u64 *found_objectid);
 int btrfs_find_dead_roots(struct btrfs_root *root, u64 objectid,
                           struct btrfs_root *latest_root);
 /* dir-item.c */
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index c0e67bde8428..8e69b5acfeff 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2422,6 +2422,85 @@ truncate_racing:
 }
 
 /*
+ * The back references tell us which tree holds a ref on a block,
+ * but it is possible for the tree root field in the reference to
+ * reflect the original root before a snapshot was made.  In this
+ * case we should search through all the children of a given root
+ * to find potential holders of references on a block.
+ *
+ * Instead, we do something a little less fancy and just search
+ * all the roots for a given key/block combination.
+ */
+static int find_root_for_ref(struct btrfs_root *root,
+                             struct btrfs_path *path,
+                             struct btrfs_key *key0,
+                             int level,
+                             int file_key,
+                             struct btrfs_root **found_root,
+                             u64 bytenr)
+{
+        struct btrfs_key root_location;
+        struct btrfs_root *cur_root = *found_root;
+        struct btrfs_file_extent_item *file_extent;
+        u64 root_search_start = BTRFS_FS_TREE_OBJECTID;
+        u64 found_bytenr;
+        int ret;
+        int i;
+
+        root_location.offset = (u64)-1;
+        root_location.type = BTRFS_ROOT_ITEM_KEY;
+        path->lowest_level = level;
+        path->reada = 0;
+        while(1) {
+                ret = btrfs_search_slot(NULL, cur_root, key0, path, 0, 0);
+                found_bytenr = 0;
+                if (ret == 0 && file_key) {
+                        struct extent_buffer *leaf = path->nodes[0];
+                        file_extent = btrfs_item_ptr(leaf, path->slots[0],
+                                             struct btrfs_file_extent_item);
+                        if (btrfs_file_extent_type(leaf, file_extent) ==
+                            BTRFS_FILE_EXTENT_REG) {
+                                found_bytenr =
+                                        btrfs_file_extent_disk_bytenr(leaf,
+                                                               file_extent);
+                       }
+                } else if (ret == 0) {
+                        if (path->nodes[level])
+                                found_bytenr = path->nodes[level]->start;
+                }
+
+                for (i = level; i < BTRFS_MAX_LEVEL; i++) {
+                        if (!path->nodes[i])
+                                break;
+                        free_extent_buffer(path->nodes[i]);
+                        path->nodes[i] = NULL;
+                }
+                btrfs_release_path(cur_root, path);
+
+                if (found_bytenr == bytenr) {
+                        *found_root = cur_root;
+                        ret = 0;
+                        goto out;
+                }
+                ret = btrfs_search_root(root->fs_info->tree_root,
+                                        root_search_start, &root_search_start);
+                if (ret)
+                        break;
+
+                root_location.objectid = root_search_start;
+                cur_root = btrfs_read_fs_root_no_name(root->fs_info,
+                                                      &root_location);
+                if (!cur_root) {
+                        ret = 1;
+                        break;
+                }
+        }
+out:
+        path->lowest_level = 0;
+        return ret;
+}
+
+/*
  * note, this releases the path
  */
 static int noinline relocate_one_reference(struct btrfs_root *extent_root,
@@ -2430,13 +2509,15 @@ static int noinline relocate_one_reference(struct btrfs_root *extent_root,
 {
         struct inode *inode;
         struct btrfs_root *found_root;
-        struct btrfs_key *root_location;
+        struct btrfs_key root_location;
+        struct btrfs_key found_key;
         struct btrfs_extent_ref *ref;
         u64 ref_root;
         u64 ref_gen;
         u64 ref_objectid;
         u64 ref_offset;
         int ret;
+        int level;
 
         ref = btrfs_item_ptr(path->nodes[0], path->slots[0],
                              struct btrfs_extent_ref);
@@ -2446,20 +2527,30 @@ static int noinline relocate_one_reference(struct btrfs_root *extent_root,
         ref_offset = btrfs_ref_offset(path->nodes[0], ref);
         btrfs_release_path(extent_root, path);
 
-        root_location = kmalloc(sizeof(*root_location), GFP_NOFS);
-        root_location->objectid = ref_root;
+        root_location.objectid = ref_root;
         if (ref_gen == 0)
-                root_location->offset = 0;
+                root_location.offset = 0;
         else
-                root_location->offset = (u64)-1;
-        root_location->type = BTRFS_ROOT_ITEM_KEY;
+                root_location.offset = (u64)-1;
+        root_location.type = BTRFS_ROOT_ITEM_KEY;
 
         found_root = btrfs_read_fs_root_no_name(extent_root->fs_info,
-                                                root_location);
+                                                &root_location);
         BUG_ON(!found_root);
-        kfree(root_location);
 
         if (ref_objectid >= BTRFS_FIRST_FREE_OBJECTID) {
+                found_key.objectid = ref_objectid;
+                found_key.type = BTRFS_EXTENT_DATA_KEY;
+                found_key.offset = ref_offset;
+                level = 0;
+
+                ret = find_root_for_ref(extent_root, path, &found_key,
+                                        level, 1, &found_root,
+                                        extent_key->objectid);
+
+                if (ret)
+                        goto out;
+
                 mutex_unlock(&extent_root->fs_info->fs_mutex);
                 inode = btrfs_iget_locked(extent_root->fs_info->sb,
                                           ref_objectid, found_root);
@@ -2485,12 +2576,9 @@ static int noinline relocate_one_reference(struct btrfs_root *extent_root,
                 mutex_lock(&extent_root->fs_info->fs_mutex);
         } else {
                 struct btrfs_trans_handle *trans;
-                struct btrfs_key found_key;
                 struct extent_buffer *eb;
-                int level;
                 int i;
 
-                trans = btrfs_start_transaction(found_root, 1);
                 eb = read_tree_block(found_root, extent_key->objectid,
                                      extent_key->offset);
                 level = btrfs_header_level(eb);
@@ -2502,6 +2590,15 @@ static int noinline relocate_one_reference(struct btrfs_root *extent_root,
 
                 free_extent_buffer(eb);
 
+                ret = find_root_for_ref(extent_root, path, &found_key,
+                                        level, 0, &found_root,
+                                        extent_key->objectid);
+
+                if (ret)
+                        goto out;
+
+                trans = btrfs_start_transaction(found_root, 1);
+
                 path->lowest_level = level;
                 path->reada = 2;
                 ret = btrfs_search_slot(trans, found_root, &found_key, path,
@@ -2578,6 +2675,7 @@ static int noinline relocate_one_extent(struct btrfs_root *extent_root,
                         }
                         if (ret < 0)
                                 goto out;
+                        leaf = path->nodes[0];
                 }
 
                 btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
diff --git a/fs/btrfs/root-tree.c b/fs/btrfs/root-tree.c
index 08f19ec88092..8bf21ba0a43b 100644
--- a/fs/btrfs/root-tree.c
+++ b/fs/btrfs/root-tree.c
@@ -21,6 +21,51 @@
 #include "disk-io.h"
 #include "print-tree.h"
 
+/*
+ * returns 0 on finding something, 1 if no more roots are there
+ * and < 0 on error
+ */
+int btrfs_search_root(struct btrfs_root *root, u64 search_start,
+                      u64 *found_objectid)
+{
+        struct btrfs_path *path;
+        struct btrfs_key search_key;
+        int ret;
+
+        root = root->fs_info->tree_root;
+        search_key.objectid = search_start;
+        search_key.type = (u8)-1;
+        search_key.offset = (u64)-1;
+
+        path = btrfs_alloc_path();
+        BUG_ON(!path);
+again:
+        ret = btrfs_search_slot(NULL, root, &search_key, path, 0, 0);
+        if (ret < 0)
+                goto out;
+        if (ret == 0) {
+                ret = 1;
+                goto out;
+        }
+        if (path->slots[0] >= btrfs_header_nritems(path->nodes[0])) {
+                ret = btrfs_next_leaf(root, path);
+                if (ret)
+                        goto out;
+        }
+        btrfs_item_key_to_cpu(path->nodes[0], &search_key, path->slots[0]);
+        if (search_key.type != BTRFS_ROOT_ITEM_KEY) {
+                search_key.offset++;
+                btrfs_release_path(root, path);
+                goto again;
+        }
+        ret = 0;
+        *found_objectid = search_key.objectid;
+
+out:
+        btrfs_free_path(path);
+        return ret;
+}
+
 int btrfs_find_last_root(struct btrfs_root *root, u64 objectid,
                         struct btrfs_root_item *item, struct btrfs_key *key)
 {
@@ -55,7 +100,6 @@ int btrfs_find_last_root(struct btrfs_root *root, u64 objectid,
         memcpy(key, &found_key, sizeof(found_key));
         ret = 0;
 out:
-        btrfs_release_path(root, path);
         btrfs_free_path(path);
         return ret;
 }