MDEV-28457 Crash in page_dir_find_owner_slot()

A prominent remaining source of crashes on corrupted index pages
is page directory corruption.

A frequent caller of page_dir_find_owner_slot() is page_rec_get_prev().
Some of those calls can be replaced with simpler logic that is less
prone to fail.

page_dir_find_owner_slot(),
page_rec_get_prev(), page_rec_get_prev_const(),
btr_pcur_move_to_prev(), btr_pcur_move_to_prev_on_page(),
btr_cur_upd_rec_sys(),
page_delete_rec_list_end(),
rtr_page_copy_rec_list_end_no_locks(),
rtr_page_copy_rec_list_start_no_locks(): Return an error code on failure.

fil_space_t::io(), buf_page_get_low(): Use DB_CORRUPTION for
out-of-bounds page reads.

PageBulk::getSplitRec(), PageBulk::copyOut(): Simplify the code.

btr_validate_level(): Prevent some more CHECK TABLE crashes on
corrupted pages.

btr_block_get(), btr_pcur_move_to_next_page(): Implement some checks that
were previously only part of IndexPurge::next().

IndexPurge::next(): Use btr_pcur_move_to_next_page().

1 files changed, 3 insertions, 4 deletions

diff --git a/storage/innobase/include/btr0pcur.inl b/storage/innobase/include/btr0pcur.inl
index fd4eeb9392a..b21de209760 100644
--- a/storage/innobase/include/btr0pcur.inl
+++ b/storage/innobase/include/btr0pcur.inl
@@ -171,17 +171,16 @@ btr_pcur_move_to_next_on_page(
 /*********************************************************//**
 Moves the persistent cursor to the previous record on the same page. */
 UNIV_INLINE
-void
+rec_t*
 btr_pcur_move_to_prev_on_page(
 /*==========================*/
 	btr_pcur_t*	cursor)	/*!< in/out: persistent cursor */
 {
 	ut_ad(cursor->pos_state == BTR_PCUR_IS_POSITIONED);
 	ut_ad(cursor->latch_mode != BTR_NO_LATCHES);
-
-	page_cur_move_to_prev(btr_pcur_get_page_cur(cursor));
-
 	cursor->old_stored = false;
+
+	return page_cur_move_to_prev(btr_pcur_get_page_cur(cursor));
 }
 
 /*********************************************************//**