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.
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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