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Btrfs: bugfix: ignore the wrong key for indirect tree block backrefs
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The key we store with a tree block backref is only a hint. It is set when
the ref is created and can remain correct for a long time. As the tree is
rebalanced, however, eventually the key no longer points to the correct
destination.

With this patch, we change find_parent_nodes to no longer add keys unless it
knows for sure they're correct (e.g. because they're for an extent data
backref). Then when we later encounter a backref ref with no parent and no
key set, we grab the block and take the first key from the block itself.

Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>
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Jan Schmidt committed May 26, 2012
1 parent dadcaf7 commit d5c88b7
Showing 1 changed file with 135 additions and 50 deletions.
185 changes: 135 additions & 50 deletions fs/btrfs/backref.c
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Original file line number Diff line number Diff line change
Expand Up @@ -30,16 +30,55 @@
struct __prelim_ref {
struct list_head list;
u64 root_id;
struct btrfs_key key;
struct btrfs_key key_for_search;
int level;
int count;
u64 parent;
u64 wanted_disk_byte;
};

/*
* the rules for all callers of this function are:
* - obtaining the parent is the goal
* - if you add a key, you must know that it is a correct key
* - if you cannot add the parent or a correct key, then we will look into the
* block later to set a correct key
*
* delayed refs
* ============
* backref type | shared | indirect | shared | indirect
* information | tree | tree | data | data
* --------------------+--------+----------+--------+----------
* parent logical | y | - | - | -
* key to resolve | - | y | y | y
* tree block logical | - | - | - | -
* root for resolving | y | y | y | y
*
* - column 1: we've the parent -> done
* - column 2, 3, 4: we use the key to find the parent
*
* on disk refs (inline or keyed)
* ==============================
* backref type | shared | indirect | shared | indirect
* information | tree | tree | data | data
* --------------------+--------+----------+--------+----------
* parent logical | y | - | y | -
* key to resolve | - | - | - | y
* tree block logical | y | y | y | y
* root for resolving | - | y | y | y
*
* - column 1, 3: we've the parent -> done
* - column 2: we take the first key from the block to find the parent
* (see __add_missing_keys)
* - column 4: we use the key to find the parent
*
* additional information that's available but not required to find the parent
* block might help in merging entries to gain some speed.
*/

static int __add_prelim_ref(struct list_head *head, u64 root_id,
struct btrfs_key *key, int level, u64 parent,
u64 wanted_disk_byte, int count)
struct btrfs_key *key, int level,
u64 parent, u64 wanted_disk_byte, int count)
{
struct __prelim_ref *ref;

Expand All @@ -50,9 +89,9 @@ static int __add_prelim_ref(struct list_head *head, u64 root_id,

ref->root_id = root_id;
if (key)
ref->key = *key;
ref->key_for_search = *key;
else
memset(&ref->key, 0, sizeof(ref->key));
memset(&ref->key_for_search, 0, sizeof(ref->key_for_search));

ref->level = level;
ref->count = count;
Expand Down Expand Up @@ -152,12 +191,13 @@ static int __resolve_indirect_ref(struct btrfs_fs_info *fs_info,
goto out;

path->lowest_level = level;
ret = btrfs_search_slot(NULL, root, &ref->key, path, 0, 0);
ret = btrfs_search_slot(NULL, root, &ref->key_for_search, path, 0, 0);
pr_debug("search slot in root %llu (level %d, ref count %d) returned "
"%d for key (%llu %u %llu)\n",
(unsigned long long)ref->root_id, level, ref->count, ret,
(unsigned long long)ref->key.objectid, ref->key.type,
(unsigned long long)ref->key.offset);
(unsigned long long)ref->key_for_search.objectid,
ref->key_for_search.type,
(unsigned long long)ref->key_for_search.offset);
if (ret < 0)
goto out;

Expand Down Expand Up @@ -248,10 +288,65 @@ static int __resolve_indirect_refs(struct btrfs_fs_info *fs_info,
return ret;
}

static inline int ref_for_same_block(struct __prelim_ref *ref1,
struct __prelim_ref *ref2)
{
if (ref1->level != ref2->level)
return 0;
if (ref1->root_id != ref2->root_id)
return 0;
if (ref1->key_for_search.type != ref2->key_for_search.type)
return 0;
if (ref1->key_for_search.objectid != ref2->key_for_search.objectid)
return 0;
if (ref1->key_for_search.offset != ref2->key_for_search.offset)
return 0;
if (ref1->parent != ref2->parent)
return 0;

return 1;
}

/*
* read tree blocks and add keys where required.
*/
static int __add_missing_keys(struct btrfs_fs_info *fs_info,
struct list_head *head)
{
struct list_head *pos;
struct extent_buffer *eb;

list_for_each(pos, head) {
struct __prelim_ref *ref;
ref = list_entry(pos, struct __prelim_ref, list);

if (ref->parent)
continue;
if (ref->key_for_search.type)
continue;
BUG_ON(!ref->wanted_disk_byte);
eb = read_tree_block(fs_info->tree_root, ref->wanted_disk_byte,
fs_info->tree_root->leafsize, 0);
BUG_ON(!eb);
btrfs_tree_read_lock(eb);
if (btrfs_header_level(eb) == 0)
btrfs_item_key_to_cpu(eb, &ref->key_for_search, 0);
else
btrfs_node_key_to_cpu(eb, &ref->key_for_search, 0);
btrfs_tree_read_unlock(eb);
free_extent_buffer(eb);
}
return 0;
}

/*
* merge two lists of backrefs and adjust counts accordingly
*
* mode = 1: merge identical keys, if key is set
* FIXME: if we add more keys in __add_prelim_ref, we can merge more here.
* additionally, we could even add a key range for the blocks we
* looked into to merge even more (-> replace unresolved refs by those
* having a parent).
* mode = 2: merge identical parents
*/
static int __merge_refs(struct list_head *head, int mode)
Expand All @@ -265,20 +360,21 @@ static int __merge_refs(struct list_head *head, int mode)

ref1 = list_entry(pos1, struct __prelim_ref, list);

if (mode == 1 && ref1->key.type == 0)
continue;
for (pos2 = pos1->next, n2 = pos2->next; pos2 != head;
pos2 = n2, n2 = pos2->next) {
struct __prelim_ref *ref2;
struct __prelim_ref *xchg;

ref2 = list_entry(pos2, struct __prelim_ref, list);

if (mode == 1) {
if (memcmp(&ref1->key, &ref2->key,
sizeof(ref1->key)) ||
ref1->level != ref2->level ||
ref1->root_id != ref2->root_id)
if (!ref_for_same_block(ref1, ref2))
continue;
if (!ref1->parent && ref2->parent) {
xchg = ref1;
ref1 = ref2;
ref2 = xchg;
}
ref1->count += ref2->count;
} else {
if (ref1->parent != ref2->parent)
Expand All @@ -298,16 +394,17 @@ static int __merge_refs(struct list_head *head, int mode)
* smaller or equal that seq to the list
*/
static int __add_delayed_refs(struct btrfs_delayed_ref_head *head, u64 seq,
struct btrfs_key *info_key,
struct list_head *prefs)
{
struct btrfs_delayed_extent_op *extent_op = head->extent_op;
struct rb_node *n = &head->node.rb_node;
struct btrfs_key key;
struct btrfs_key op_key = {0};
int sgn;
int ret = 0;

if (extent_op && extent_op->update_key)
btrfs_disk_key_to_cpu(info_key, &extent_op->key);
btrfs_disk_key_to_cpu(&op_key, &extent_op->key);

while ((n = rb_prev(n))) {
struct btrfs_delayed_ref_node *node;
Expand Down Expand Up @@ -339,7 +436,7 @@ static int __add_delayed_refs(struct btrfs_delayed_ref_head *head, u64 seq,
struct btrfs_delayed_tree_ref *ref;

ref = btrfs_delayed_node_to_tree_ref(node);
ret = __add_prelim_ref(prefs, ref->root, info_key,
ret = __add_prelim_ref(prefs, ref->root, &op_key,
ref->level + 1, 0, node->bytenr,
node->ref_mod * sgn);
break;
Expand All @@ -348,16 +445,14 @@ static int __add_delayed_refs(struct btrfs_delayed_ref_head *head, u64 seq,
struct btrfs_delayed_tree_ref *ref;

ref = btrfs_delayed_node_to_tree_ref(node);
ret = __add_prelim_ref(prefs, ref->root, info_key,
ret = __add_prelim_ref(prefs, ref->root, NULL,
ref->level + 1, ref->parent,
node->bytenr,
node->ref_mod * sgn);
break;
}
case BTRFS_EXTENT_DATA_REF_KEY: {
struct btrfs_delayed_data_ref *ref;
struct btrfs_key key;

ref = btrfs_delayed_node_to_data_ref(node);

key.objectid = ref->objectid;
Expand All @@ -370,7 +465,6 @@ static int __add_delayed_refs(struct btrfs_delayed_ref_head *head, u64 seq,
}
case BTRFS_SHARED_DATA_REF_KEY: {
struct btrfs_delayed_data_ref *ref;
struct btrfs_key key;

ref = btrfs_delayed_node_to_data_ref(node);

Expand All @@ -396,8 +490,7 @@ static int __add_delayed_refs(struct btrfs_delayed_ref_head *head, u64 seq,
*/
static int __add_inline_refs(struct btrfs_fs_info *fs_info,
struct btrfs_path *path, u64 bytenr,
struct btrfs_key *info_key, int *info_level,
struct list_head *prefs)
int *info_level, struct list_head *prefs)
{
int ret = 0;
int slot;
Expand Down Expand Up @@ -426,12 +519,9 @@ static int __add_inline_refs(struct btrfs_fs_info *fs_info,

if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
struct btrfs_tree_block_info *info;
struct btrfs_disk_key disk_key;

info = (struct btrfs_tree_block_info *)ptr;
*info_level = btrfs_tree_block_level(leaf, info);
btrfs_tree_block_key(leaf, info, &disk_key);
btrfs_disk_key_to_cpu(info_key, &disk_key);
ptr += sizeof(struct btrfs_tree_block_info);
BUG_ON(ptr > end);
} else {
Expand All @@ -449,7 +539,7 @@ static int __add_inline_refs(struct btrfs_fs_info *fs_info,

switch (type) {
case BTRFS_SHARED_BLOCK_REF_KEY:
ret = __add_prelim_ref(prefs, 0, info_key,
ret = __add_prelim_ref(prefs, 0, NULL,
*info_level + 1, offset,
bytenr, 1);
break;
Expand All @@ -464,8 +554,9 @@ static int __add_inline_refs(struct btrfs_fs_info *fs_info,
break;
}
case BTRFS_TREE_BLOCK_REF_KEY:
ret = __add_prelim_ref(prefs, offset, info_key,
*info_level + 1, 0, bytenr, 1);
ret = __add_prelim_ref(prefs, offset, NULL,
*info_level + 1, 0,
bytenr, 1);
break;
case BTRFS_EXTENT_DATA_REF_KEY: {
struct btrfs_extent_data_ref *dref;
Expand All @@ -479,8 +570,8 @@ static int __add_inline_refs(struct btrfs_fs_info *fs_info,
key.type = BTRFS_EXTENT_DATA_KEY;
key.offset = btrfs_extent_data_ref_offset(leaf, dref);
root = btrfs_extent_data_ref_root(leaf, dref);
ret = __add_prelim_ref(prefs, root, &key, 0, 0, bytenr,
count);
ret = __add_prelim_ref(prefs, root, &key, 0, 0,
bytenr, count);
break;
}
default:
Expand All @@ -498,8 +589,7 @@ static int __add_inline_refs(struct btrfs_fs_info *fs_info,
*/
static int __add_keyed_refs(struct btrfs_fs_info *fs_info,
struct btrfs_path *path, u64 bytenr,
struct btrfs_key *info_key, int info_level,
struct list_head *prefs)
int info_level, struct list_head *prefs)
{
struct btrfs_root *extent_root = fs_info->extent_root;
int ret;
Expand Down Expand Up @@ -529,7 +619,7 @@ static int __add_keyed_refs(struct btrfs_fs_info *fs_info,

switch (key.type) {
case BTRFS_SHARED_BLOCK_REF_KEY:
ret = __add_prelim_ref(prefs, 0, info_key,
ret = __add_prelim_ref(prefs, 0, NULL,
info_level + 1, key.offset,
bytenr, 1);
break;
Expand All @@ -545,8 +635,9 @@ static int __add_keyed_refs(struct btrfs_fs_info *fs_info,
break;
}
case BTRFS_TREE_BLOCK_REF_KEY:
ret = __add_prelim_ref(prefs, key.offset, info_key,
info_level + 1, 0, bytenr, 1);
ret = __add_prelim_ref(prefs, key.offset, NULL,
info_level + 1, 0,
bytenr, 1);
break;
case BTRFS_EXTENT_DATA_REF_KEY: {
struct btrfs_extent_data_ref *dref;
Expand All @@ -562,7 +653,7 @@ static int __add_keyed_refs(struct btrfs_fs_info *fs_info,
key.offset = btrfs_extent_data_ref_offset(leaf, dref);
root = btrfs_extent_data_ref_root(leaf, dref);
ret = __add_prelim_ref(prefs, root, &key, 0, 0,
bytenr, count);
bytenr, count);
break;
}
default:
Expand All @@ -588,7 +679,6 @@ static int find_parent_nodes(struct btrfs_trans_handle *trans,
{
struct btrfs_key key;
struct btrfs_path *path;
struct btrfs_key info_key = { 0 };
struct btrfs_delayed_ref_root *delayed_refs = NULL;
struct btrfs_delayed_ref_head *head;
int info_level = 0;
Expand Down Expand Up @@ -647,8 +737,7 @@ static int find_parent_nodes(struct btrfs_trans_handle *trans,
btrfs_put_delayed_ref(&head->node);
goto again;
}
ret = __add_delayed_refs(head, seq, &info_key,
&prefs_delayed);
ret = __add_delayed_refs(head, seq, &prefs_delayed);
if (ret) {
spin_unlock(&delayed_refs->lock);
goto out;
Expand All @@ -668,27 +757,23 @@ static int find_parent_nodes(struct btrfs_trans_handle *trans,
if (key.objectid == bytenr &&
key.type == BTRFS_EXTENT_ITEM_KEY) {
ret = __add_inline_refs(fs_info, path, bytenr,
&info_key, &info_level, &prefs);
&info_level, &prefs);
if (ret)
goto out;
ret = __add_keyed_refs(fs_info, path, bytenr, &info_key,
ret = __add_keyed_refs(fs_info, path, bytenr,
info_level, &prefs);
if (ret)
goto out;
}
}
btrfs_release_path(path);

/*
* when adding the delayed refs above, the info_key might not have
* been known yet. Go over the list and replace the missing keys
*/
list_for_each_entry(ref, &prefs_delayed, list) {
if ((ref->key.offset | ref->key.type | ref->key.objectid) == 0)
memcpy(&ref->key, &info_key, sizeof(ref->key));
}
list_splice_init(&prefs_delayed, &prefs);

ret = __add_missing_keys(fs_info, &prefs);
if (ret)
goto out;

ret = __merge_refs(&prefs, 1);
if (ret)
goto out;
Expand Down

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