From 42a5710acadac8bab9383c759affa3a4ff02d895 Mon Sep 17 00:00:00 2001 From: Su Yue Date: Wed, 25 Apr 2018 13:19:24 +0800 Subject: [PATCH] btrfs-progs: do not merge tree block refs have different root_id For an extent item which contains many tree block backrefs, like In 020-extent-ref-cases/keyed_block_ref.img item 10 key (29470720 METADATA_ITEM 0) itemoff 3450 itemsize 222 refs 23 gen 10 flags TREE_BLOCK tree block skinny level 0 tree block backref root 278 tree block backref root 277 tree block backref root 276 tree block backref root 275 tree block backref root 274 tree block backref root 273 tree block backref root 272 tree block backref root 271 tree block backref root 270 tree block backref root 269 tree block backref root 268 tree block backref root 267 tree block backref root 266 tree block backref root 265 tree block backref root 264 tree block backref root 263 tree block backref root 262 tree block backref root 261 tree block backref root 260 tree block backref root 259 tree block backref root 258 tree block backref root 257 In find_parent_nodes(), these refs's parents are 0, then __merge_refs will merge refs to one ref. It causes only one root to be returned. So, if both parents are 0, do not merge refs. Lowmem check calls find_parent_nodes frequently to decide whether check an extent buffer or not. The bug affects bytes accounting. Signed-off-by: Su Yue Reviewed-by: Qu Wenruo Signed-off-by: David Sterba --- backref.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/backref.c b/backref.c index 51553c70..23a394ed 100644 --- a/backref.c +++ b/backref.c @@ -505,6 +505,12 @@ static void __merge_refs(struct pref_state *prefstate, int mode) if (!ref_for_same_block(ref1, ref2)) continue; } else { + /* + * Parent == 0 means that the ref is tree block + * backref or its parent is unresolved. + */ + if (!ref1->parent || !ref2->parent) + continue; if (ref1->parent != ref2->parent) continue; }