1 files changed, 40 insertions, 6 deletions

diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index ed1f7ce7219a..e0ef92f91d66 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -2833,6 +2833,7 @@ static int log_one_extent(struct btrfs_trans_handle *trans,
         struct btrfs_file_extent_item *fi;
         struct btrfs_key key;
         u64 start = em->mod_start;
+        u64 search_start = start;
         u64 len = em->mod_len;
         u64 num_bytes;
         int nritems;
@@ -2848,23 +2849,55 @@ static int log_one_extent(struct btrfs_trans_handle *trans,
         while (len) {
                 if (args->nr)
                         goto next_slot;
+again:
                 key.objectid = btrfs_ino(inode);
                 key.type = BTRFS_EXTENT_DATA_KEY;
-                key.offset = start;
+                key.offset = search_start;
 
                 ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
                 if (ret < 0)
                         return ret;
+
                 if (ret) {
                         /*
-                         * This shouldn't happen, but it might so warn and
-                         * return an error.
+                         * A rare case were we can have an em for a section of a
+                         * larger extent so we need to make sure that this em
+                         * falls within the extent we've found.  If not we just
+                         * bail and go back to ye-olde way of doing things but
+                         * it happens often enough in testing that we need to do
+                         * this dance to make sure.
                          */
-                        WARN_ON(1);
-                        return -ENOENT;
+                        do {
+                                if (path->slots[0] == 0) {
+                                        btrfs_release_path(path);
+                                        if (search_start == 0)
+                                                return -ENOENT;
+                                        search_start--;
+                                        goto again;
+                                }
+
+                                path->slots[0]--;
+                                btrfs_item_key_to_cpu(path->nodes[0], &key,
+                                                      path->slots[0]);
+                                if (key.objectid != btrfs_ino(inode) ||
+                                    key.type != BTRFS_EXTENT_DATA_KEY) {
+                                        btrfs_release_path(path);
+                                        return -ENOENT;
+                                }
+                        } while (key.offset > start);
+
+                        fi = btrfs_item_ptr(path->nodes[0], path->slots[0],
+                                            struct btrfs_file_extent_item);
+                        num_bytes = btrfs_file_extent_num_bytes(path->nodes[0],
+                                                                fi);
+                        if (key.offset + num_bytes <= start) {
+                                btrfs_release_path(path);
+                                return -ENOENT;
+                        }
                 }
                 args->src = path->nodes[0];
 next_slot:
+                btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
                 fi = btrfs_item_ptr(args->src, path->slots[0],
                                     struct btrfs_file_extent_item);
                 if (args->nr &&
@@ -2898,8 +2931,9 @@ next_slot:
                 } else {
                         len -= num_bytes;
                 }
-                start += btrfs_file_extent_num_bytes(args->src, fi);
+                start = key.offset + num_bytes;
                 args->next_offset = start;
+                search_start = start;
 
                 if (path->slots[0] < nritems) {
                         if (len)