MDEV-17843 Assertion `page_rec_is_leaf(rec)' failed in lock_rec_queue_validate upon SHOW ENGINE INNODB STATUS

lock_validate() accumulates page ids under locked lock_sys->mutex, then releases the latch, and invokes lock_rec_block_validate() for each page. Some other thread has ability to add/remove locks and change pages between releasing the latch in lock_validate() and acquiring it in lock_rec_validate_page(). lock_rec_validate_page() can invoke lock_rec_queue_validate() for non-locked supremum, what can cause ut_ad(page_rec_is_leaf(rec)) failure in lock_rec_queue_validate(). The fix is to invoke lock_rec_queue_validate() only for locked records in lock_rec_validate_page(). The error message in lock_rec_block_validate() is not necessary as BUF_GET_POSSIBLY_FREED mode is used to get block from buffer pool, and this is not error if a block was evicted. The test case would require new debug sync point. I think it's not necessary as the fixed code is debug-only.

Author: vlad-lesin

storage/innobase/lock/lock0lock.cc

@@ -5050,25 +5050,25 @@ lock_rec_validate_page(
 holding a space->latch. */
 if (!sync_check_find(SYNC_FSP))
 for (i = nth_bit; i < lock_rec_get_n_bits(lock); i++) {
-
-if (i == PAGE_HEAP_NO_SUPREMUM
- || lock_rec_get_nth_bit(lock, i)) {
+bool locked = lock_rec_get_nth_bit(lock, i);
+if (locked || i == PAGE_HEAP_NO_SUPREMUM) {
 
 rec = page_find_rec_with_heap_no(block->frame, i);
 ut_a(rec);
-ut_ad(!lock_rec_get_nth_bit(lock, i)
- || page_rec_is_leaf(rec));
-offsets = rec_get_offsets(rec, lock->index, offsets,
- lock->index->n_core_fields,
- ULINT_UNDEFINED, &heap);
+ut_ad(!locked || page_rec_is_leaf(rec));
 
 /* If this thread is holding the file space
 latch (fil_space_t::latch), the following
 check WILL break the latching order and may
 cause a deadlock of threads. */
 
-lock_rec_queue_validate(
-TRUE, block, rec, lock->index, offsets);
+if (locked) {
+offsets = rec_get_offsets(rec, lock->index,
+offsets, lock->index->n_core_fields,
+ULINT_UNDEFINED, &heap);
+lock_rec_queue_validate(TRUE, block, rec,
+lock->index, offsets);
+}
 
 nth_bit = i + 1;
 
@@ -5161,13 +5161,6 @@ lock_rec_block_validate(
 BUF_GET_POSSIBLY_FREED,
 __FILE__, __LINE__, &mtr, &err);
 
-if (err != DB_SUCCESS) {
-ib::error() << "Lock rec block validate failed for tablespace "
- << space->name
- << " space_id " << space_id
- << " page_no " << page_no << " err " << err;
-}
-
 if (block) {
 buf_block_dbg_add_level(block, SYNC_NO_ORDER_CHECK);