[PATCH 38/40] btrfs: qgroup: Introduce verification for function to ensure old roots ulist matches btrfs_find_all_roots() result

Qu Wenruo
2020-03-23T10:26:11Z

This patch will introduce a new function, verify_old_roots(), for qgroup
to verify the backref cache based result and old btrfs_find_all_roots()
result.

Since it will impact performance heavily as we are doing two different
backref walk, this verification will only be enabled for
CONFIG_BTRFS_FS_CHECK_INTEGRITY.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
fs/btrfs/qgroup.c | 72 +++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 72 insertions(+)

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 3c25e17f0979..19d68e8397d0 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -1831,6 +1831,78 @@ static int get_tree_info(struct btrfs_fs_info *fs_info,
return ret;
}

+#ifdef CONFIG_BTRFS_FS_CHECK_INTEGRITY
+/*
+ * Compare the result with old btrfs_find_all_roots() to ensure the new backref
+ * cache based result is correct.
+ */
+static int verify_old_roots(struct btrfs_fs_info *fs_info,
+ struct ulist *result, u64 bytenr)
+{
+ struct ulist *old;
+ struct ulist_iterator uiter;
+ struct ulist_node *unode;
+ bool not_fstree = false;
+ int ret = 0;
+
+ ret = btrfs_find_all_roots(NULL, fs_info, bytenr, 0, &old, true);
+ if (ret < 0)
+ return ret;
+
+ /*
+ * Check the first node, as find_all_roots() will also return
+ * non-subvolume tree owner.
+ * Since subvolume tree block won't be shared with non-subvolume
+ * trees, if we find a non-subolume tree root, we don't need
+ * to verify at all.
+ */
+ ULIST_ITER_INIT(&uiter);
+ while ((unode = ulist_next(old, &uiter))) {
+ if (!is_fstree(unode->val))
+ not_fstree = true;
+ break;
+ }
+
+ if (not_fstree && result->nnodes != 0) {
+ btrfs_err(fs_info,
+"qgroup backref cached error, bytenr=%llu found cached node for non-fs tree",
+ bytenr);
+ ret = -EUCLEAN;
+ goto out;
+ }
+ if (not_fstree)
+ goto out;
+
+ if (result->nnodes != old->nnodes) {
+ btrfs_err(fs_info,
+"qgroup backref cache error, bytenr=%llu nr nodes mismatch, old method=%lu cache method=%lu",
+ bytenr, old->nnodes, result->nnodes);
+ ret = -EUCLEAN;
+ goto out;
+ }
+ ULIST_ITER_INIT(&uiter);
+ while ((unode = ulist_next(result, &uiter))) {
+ /*
+ * @result and @old have the same amount of nodes, so if we
+ * delete each @result node from @old, we either delete all
+ * nodes from @old (verification pass), or we will hit
+ * a missing node (verification failure).
+ */
+ ret = ulist_del(old, unode->val, 0);
+ if (ret) {
+ btrfs_err(fs_info,
+ "qgroup backref cache error, bytenr=%llu root %llu not found in cached result",
+ bytenr, unode->val);
+ ret = -EUCLEAN;
+ goto out;
+ }
+ }
+out:
+ ulist_free(old);
+ return ret;
+}
+#endif
+
/* Iterate all roots in the backref_cache, and add root objectid into @roots */
static int iterate_all_roots(struct btrfs_backref_node *node,
struct ulist *roots)
--
2.25.2