btrfs: add cond_resched() calls when resolving backrefs

Since backref resolution is CPU-intensive, the cond_resched calls
should help alleviate soft lockup occurences.

Signed-off-by: Edmund Nadolski <enadolski@suse.com>
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/backref.c

@@ -660,6 +660,7 @@ static int resolve_indirect_refs(struct btrfs_fs_info *fs_info,
 		prelim_ref_insert(fs_info, &preftrees->direct, ref);
 
 		ulist_reinit(parents);
+		cond_resched();
 	}
 out:
 	ulist_free(parents);
@@ -702,6 +703,7 @@ static int add_missing_keys(struct btrfs_fs_info *fs_info,
 		btrfs_tree_read_unlock(eb);
 		free_extent_buffer(eb);
 		prelim_ref_insert(fs_info, &preftrees->indirect, ref);
+		cond_resched();
 	}
 	return 0;
 }
@@ -1243,6 +1245,7 @@ again:
 			}
 			eie = NULL;
 		}
+		cond_resched();
 	}
 
 out: