On 12.04.2018 14:48, Qu Wenruo wrote:
>
>
> On 2018年04月12日 18:59, Nikolay Borisov wrote:
>>
>>
>> On 12.04.2018 13:00, Qu Wenruo wrote:
>>> The original first key check is handled in
>>> btree_read_extent_buffer_pages(), which is good enough for level check,
>>> but to verify first key, we need at least read lock on the extent
>>> buffer, or we can hit some race and cause false alert.
>>>
>>> Fix it by adding new verifcation function: btrfs_verify_first_key(),
>>> which will first check lock context of both parent and child extent
>>> buffer, and only when we have proper lock hold (write or read lock if
>> So if the extent buffer is not in commit root, i.e it's active buffer in
>> current transaction (am I right?)
>
> That's right.
>
>> then we need write lock? It's not entirely clearly from that sentence.
>
> Not really write lock. Either read or write (both spinning and blocking)
> is OK here.
>
>>
>>> extent buffer is not in commit root) we will verify the first key.
>>>
>>> Most of the verification happens in ctree.c after function call like
>>> read_tree_block(), read_node_slot() and read_block_for_search(), and
>>> only call btrfs_verify_first_key() after we acquire read/write lock.
>>>
>>> Also, since first_key check is not as good as level and could easily
>>> trigger false alerts due to lock context, put it under
>>> CONFIG_BTRFS_FS_CHECK_INTEGRITY to avoid damage to end user.
>>
>> Why is first_key check not as good as level
>
> Several reasons.
>
> 1) Level tree check can prevent loop/nodes underflow caused by level
> mismatch, but first_key can't
> One problem we're trying to solve is, when level 1 node points to
> another level 1 tree, we can still try to read next level tree block.
> Which could underflow level.
> first_key check can't really handle it.
>
> 2) first_key needs extra lock to read out needed info, while level
> check doesn't (hence easier and harder to cause false alert)
> For a given tree block, its level won't change either for active eb
> (modified in current trans) or committed eb.
> But for first_key, we need proper lock to avoid race.
>
> For short, first key check needs a lot of carefully reviewed check
> timing and error handlers, while most problem could be exposed by level
> check far before it hits first_key check.
>
>> and why could it trigger
>> false alert, given this patch allegedly implements it under proper lock
>> context, thus eliminating false positives.
>
> I mean the old and merged first_key check patch.
Right, I'd suggest you change the wording so it makes it clear that the
old patch was broken and not the concept of first_key in general
(because that's the impression I was left with).
>
> Thanks,
> Qu
>
>>
>>>
>>> Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
>>> ---
>>> fs/btrfs/ctree.c | 69 ++++++++++++++++++++++++++++++++++++++++++
>>> fs/btrfs/ctree.h | 58 +++++++++++++++++++++++++++++++++++
>>> fs/btrfs/extent-tree.c | 6 ++++
>>> fs/btrfs/qgroup.c | 5 +++
>>> fs/btrfs/ref-verify.c | 6 ++++
>>> fs/btrfs/relocation.c | 13 ++++++++
>>> 6 files changed, 157 insertions(+)
>>>
>>> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
>>> index e044b51a2789..57721aead371 100644
>>> --- a/fs/btrfs/ctree.c
>>> +++ b/fs/btrfs/ctree.c
>>> @@ -1649,6 +1649,11 @@ int btrfs_realloc_node(struct btrfs_trans_handle *trans,
>>>
>>> btrfs_tree_lock(cur);
>>> btrfs_set_lock_blocking(cur);
>>> + if (btrfs_verify_first_key(cur, parent, i)) {
>>> + err = -EUCLEAN;
>>> + btrfs_tree_unlock(cur);
>>> + free_extent_buffer(cur);
>>> + }
>>> err = __btrfs_cow_block(trans, root, cur, parent, i,
>>> &cur, search_start,
>>> min(16 * blocksize,
>>> @@ -1863,6 +1868,12 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
>>>
>>> btrfs_tree_lock(child);
>>> btrfs_set_lock_blocking(child);
>>> + if (btrfs_verify_first_key(child, mid, 0)) {
>>> + ret = -EUCLEAN;
>>> + btrfs_tree_unlock(child);
>>> + free_extent_buffer(child);
>>> + goto enospc;
>>> + }
>>> ret = btrfs_cow_block(trans, root, child, mid, 0, &child);
>>> if (ret) {
>>> btrfs_tree_unlock(child);
>>> @@ -1901,6 +1912,10 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
>>> if (left) {
>>> btrfs_tree_lock(left);
>>> btrfs_set_lock_blocking(left);
>>> + if (btrfs_verify_first_key(left, parent, pslot - 1)) {
>>> + ret = -EUCLEAN;
>>> + goto enospc;
>>> + }
>>> wret = btrfs_cow_block(trans, root, left,
>>> parent, pslot - 1, &left);
>>> if (wret) {
>>> @@ -1916,6 +1931,10 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
>>> if (right) {
>>> btrfs_tree_lock(right);
>>> btrfs_set_lock_blocking(right);
>>> + if (btrfs_verify_first_key(right, parent, pslot + 1)) {
>>> + ret = -EUCLEAN;
>>> + goto enospc;
>>> + }
>>> wret = btrfs_cow_block(trans, root, right,
>>> parent, pslot + 1, &right);
>>> if (wret) {
>>> @@ -2079,6 +2098,8 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
>>>
>>> btrfs_tree_lock(left);
>>> btrfs_set_lock_blocking(left);
>>> + if (btrfs_verify_first_key(left, parent, pslot - 1))
>>> + goto left_out;
>>>
>>> left_nr = btrfs_header_nritems(left);
>>> if (left_nr >= BTRFS_NODEPTRS_PER_BLOCK(fs_info) - 1) {
>>> @@ -2119,6 +2140,7 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
>>> }
>>> return 0;
>>> }
>>> +left_out:
>>> btrfs_tree_unlock(left);
>>> free_extent_buffer(left);
>>> }
>>> @@ -2134,6 +2156,8 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
>>>
>>> btrfs_tree_lock(right);
>>> btrfs_set_lock_blocking(right);
>>> + if (btrfs_verify_first_key(right, parent, pslot + 1))
>>> + goto right_out;
>>>
>>> right_nr = btrfs_header_nritems(right);
>>> if (right_nr >= BTRFS_NODEPTRS_PER_BLOCK(fs_info) - 1) {
>>> @@ -2174,6 +2198,7 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
>>> }
>>> return 0;
>>> }
>>> +right_out:
>>> btrfs_tree_unlock(right);
>>> free_extent_buffer(right);
>>> }
>>> @@ -2868,6 +2893,11 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root,
>>> p->locks[level] = BTRFS_READ_LOCK;
>>> }
>>> p->nodes[level] = b;
>>> + if (btrfs_verify_first_key(b, p->nodes[level + 1],
>>> + slot)) {
>>> + ret = -EUCLEAN;
>>> + goto done;
>>> + }
>>> }
>>> } else {
>>> p->slots[level] = slot;
>>> @@ -2981,6 +3011,12 @@ int btrfs_search_old_slot(struct btrfs_root *root, const struct btrfs_key *key,
>>> goto done;
>>> }
>>>
>>> + /*
>>> + * NOTE: both parent and child go through
>>> + * tree_mod_log_rewind(), first key check is no
>>> + * longer consistent. So no btrfs_verify_first_key()
>>> + * for this read_block_for_search().
>>> + */
>>> err = read_block_for_search(root, p, &b, level,
>>> slot, key);
>>> if (err == -EAGAIN)
>>> @@ -3753,6 +3789,8 @@ static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
>>>
>>> btrfs_tree_lock(right);
>>> btrfs_set_lock_blocking(right);
>>> + if (btrfs_verify_first_key(right, upper, slot + 1))
>>> + goto out_unlock;
>>>
>>> free_space = btrfs_leaf_free_space(fs_info, right);
>>> if (free_space < data_size)
>>> @@ -3987,6 +4025,10 @@ static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
>>>
>>> btrfs_tree_lock(left);
>>> btrfs_set_lock_blocking(left);
>>> + if (btrfs_verify_first_key(left, path->nodes[1], slot - 1)) {
>>> + ret = 1;
>>> + goto out;
>>> + }
>>>
>>> free_space = btrfs_leaf_free_space(fs_info, left);
>>> if (free_space < data_size) {
>>> @@ -5205,6 +5247,12 @@ int btrfs_search_forward(struct btrfs_root *root, struct btrfs_key *min_key,
>>> }
>>>
>>> btrfs_tree_read_lock(cur);
>>> + if (btrfs_verify_first_key(cur, path->nodes[level], slot)) {
>>> + btrfs_tree_read_unlock(cur);
>>> + free_extent_buffer(cur);
>>> + ret = -EUCLEAN;
>>> + goto out;
>>> + }
>>>
>>> path->locks[level - 1] = BTRFS_READ_LOCK;
>>> path->nodes[level - 1] = cur;
>>> @@ -5232,6 +5280,11 @@ static int tree_move_down(struct btrfs_fs_info *fs_info,
>>> if (IS_ERR(eb))
>>> return PTR_ERR(eb);
>>>
>>> + if (btrfs_verify_first_key(eb, path->nodes[*level],
>>> + path->slots[*level])) {
>>> + free_extent_buffer(eb);
>>> + return -EUCLEAN;
>>> + }
>>> path->nodes[*level - 1] = eb;
>>> path->slots[*level - 1] = 0;
>>> (*level)--;
>>> @@ -5786,6 +5839,14 @@ int btrfs_next_old_leaf(struct btrfs_root *root, struct btrfs_path *path,
>>> BTRFS_READ_LOCK);
>>> }
>>> next_rw_lock = BTRFS_READ_LOCK;
>>> + if (btrfs_verify_first_key(next, path->nodes[level],
>>> + slot)) {
>>> + ret = -EUCLEAN;
>>> + btrfs_tree_read_unlock(next);
>>> + free_extent_buffer(next);
>>> + btrfs_release_path(path);
>>> + goto done;
>>> + }
>>> }
>>> break;
>>> }
>>> @@ -5823,6 +5884,14 @@ int btrfs_next_old_leaf(struct btrfs_root *root, struct btrfs_path *path,
>>> BTRFS_READ_LOCK);
>>> }
>>> next_rw_lock = BTRFS_READ_LOCK;
>>> + if (btrfs_verify_first_key(next, path->nodes[level],
>>> + 0)) {
>>> + ret = -EUCLEAN;
>>> + btrfs_tree_read_unlock(next);
>>> + free_extent_buffer(next);
>>> + btrfs_release_path(path);
>>> + goto done;
>>> + }
>>> }
>>> }
>>> ret = 0;
>>> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
>>> index 0eb55825862a..033d8ae027c3 100644
>>> --- a/fs/btrfs/ctree.h
>>> +++ b/fs/btrfs/ctree.h
>>> @@ -44,6 +44,7 @@
>>> #include "extent_io.h"
>>> #include "extent_map.h"
>>> #include "async-thread.h"
>>> +#include "print-tree.h"
>>>
>>> struct btrfs_trans_handle;
>>> struct btrfs_transaction;
>>> @@ -3752,4 +3753,61 @@ static inline int btrfs_is_testing(struct btrfs_fs_info *fs_info)
>>> #endif
>>> return 0;
>>> }
>>> +
>>> +/*
>>> + * Verify the first key of an extent buffer matches with its parent pointer.
>>> + *
>>> + * For tree blocks in current transaction, caller should hold at least read lock
>>> + * for both @eb and @parent to avoid race.
>>> + * While for tree blocks in commit root, no such requirement.
>>> + */
>>> +static inline int btrfs_verify_first_key(struct extent_buffer *eb,
>>> + struct extent_buffer *parent, int slot)
>>> +{
>>> +#ifdef CONFIG_BTRFS_FS_CHECK_INTEGRITY
>>> + struct btrfs_key parent_key;
>>> + struct btrfs_key found_key;
>>> + struct btrfs_fs_info *fs_info;
>>> + u64 transid = 0;
>>> + int ret;
>>> +
>>> + if (!parent || !eb)
>>> + return 0;
>>> + fs_info = parent->fs_info;
>>> + transid = fs_info->last_trans_committed;
>>> + /*
>>> + * For first_key check, we need to ensure we have proper lock hold,
>>> + * or the content may change and cause false alert.
>>> + */
>>> + if (btrfs_header_generation(eb) > transid &&
>>> + !atomic_read(&eb->read_locks) && !atomic_read(&eb->write_locks)) {
>>> + WARN_ON(1);
>>> + return 0;
>>> + }
>>> + if (btrfs_header_generation(parent) > transid &&
>>> + !atomic_read(&parent->read_locks) &&
>>> + !atomic_read(&parent->write_locks)) {
>>> + WARN_ON(1);
>>> + return 0;
>>> + }
>>> + btrfs_node_key_to_cpu(parent, &parent_key, slot);
>>> + if (btrfs_header_level(eb))
>>> + btrfs_node_key_to_cpu(eb, &found_key, 0);
>>> + else
>>> + btrfs_item_key_to_cpu(eb, &found_key, 0);
>>> + ret = btrfs_comp_cpu_keys(&found_key, &parent_key);
>>> + if (ret) {
>>> + WARN_ON(ret);
>>> + btrfs_err(fs_info,
>>> +"tree first key mismatch detected, bytenr=%llu key expected=(%llu, %u, %llu) has=(%llu, %u, %llu)",
>>> + eb->start, parent_key.objectid, parent_key.type,
>>> + parent_key.offset, found_key.objectid,
>>> + found_key.type, found_key.offset);
>>> + }
>>> + return ret;
>>> +#else
>>> + return 0;
>>> +#endif /* CONFIG_BTRFS_FS_CHECK_INTEGRITY */
>>> +}
>>> +
>>> #endif
>>> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
>>> index f080834e4dd0..17bd22a54281 100644
>>> --- a/fs/btrfs/extent-tree.c
>>> +++ b/fs/btrfs/extent-tree.c
>>> @@ -8807,6 +8807,12 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
>>> }
>>> btrfs_tree_lock(next);
>>> btrfs_set_lock_blocking(next);
>>> + if (btrfs_verify_first_key(next, path->nodes[level],
>>> + path->slots[level])) {
>>> + btrfs_tree_unlock(next);
>>> + free_extent_buffer(next);
>>> + goto out_unlock;
>>> + }
>>> }
>>>
>>> level--;
>>> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
>>> index c7f129356966..4c53954297d8 100644
>>> --- a/fs/btrfs/qgroup.c
>>> +++ b/fs/btrfs/qgroup.c
>>> @@ -1744,6 +1744,11 @@ int btrfs_qgroup_trace_subtree(struct btrfs_trans_handle *trans,
>>>
>>> btrfs_tree_read_lock(eb);
>>> btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK);
>>> + if (btrfs_verify_first_key(eb, path->nodes[level + 1],
>>> + parent_slot)) {
>>> + ret = -EUCLEAN;
>>> + goto out;
>>> + }
>>> path->locks[level] = BTRFS_READ_LOCK_BLOCKING;
>>>
>>> ret = btrfs_qgroup_trace_extent(trans, fs_info,
>>> diff --git a/fs/btrfs/ref-verify.c b/fs/btrfs/ref-verify.c
>>> index 6d856eabf34a..b996ca1fd9dc 100644
>>> --- a/fs/btrfs/ref-verify.c
>>> +++ b/fs/btrfs/ref-verify.c
>>> @@ -593,6 +593,12 @@ static int walk_down_tree(struct btrfs_root *root, struct btrfs_path *path,
>>> }
>>> btrfs_tree_read_lock(eb);
>>> btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK);
>>> + if (btrfs_verify_first_key(eb, path->nodes[level],
>>> + path->slots[level])) {
>>> + btrfs_tree_read_unlock_blocking(eb);
>>> + free_extent_buffer(eb);
>>> + return -EUCLEAN;
>>> + }
>>> path->nodes[level-1] = eb;
>>> path->slots[level-1] = 0;
>>> path->locks[level-1] = BTRFS_READ_LOCK_BLOCKING;
>>> diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
>>> index 74db4694d776..74a088fbdac4 100644
>>> --- a/fs/btrfs/relocation.c
>>> +++ b/fs/btrfs/relocation.c
>>> @@ -1888,6 +1888,13 @@ int replace_path(struct btrfs_trans_handle *trans,
>>> break;
>>> }
>>> btrfs_tree_lock(eb);
>>> + if (btrfs_verify_first_key(eb, parent, slot)) {
>>> + btrfs_tree_unlock(eb);
>>> + free_extent_buffer(eb);
>>> + ret = -EUCLEAN;
>>> + break;
>>> + }
>>> +
>>> if (cow) {
>>> ret = btrfs_cow_block(trans, dest, eb, parent,
>>> slot, &eb);
>>> @@ -2793,6 +2800,12 @@ static int do_relocation(struct btrfs_trans_handle *trans,
>>> }
>>> btrfs_tree_lock(eb);
>>> btrfs_set_lock_blocking(eb);
>>> + if (btrfs_verify_first_key(eb, upper->eb, slot)) {
>>> + btrfs_tree_unlock(eb);
>>> + free_extent_buffer(eb);
>>> + err = -EUCLEAN;
>>> + goto next;
>>> + }
>>>
>>> if (!node->eb) {
>>> ret = btrfs_cow_block(trans, root, eb, upper->eb,
>>>
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