MDEV-17441: Pointer indirection for buf_block_t::debug_latch

This is a follow-up to commit 9581c4a8
which added a memcpy() call to rtr_copy_buf(), to copy
rw_lock_t debug_latch. This could emit a warning.

A cleaner approach is to make buf_block_t::debug_latch a pointer,
so that we can avoid copying it. An even cleaner approach would be to
redesign the InnoDB SPATIAL INDEX code so that the function
rtr_copy_buf() is not needed at all.

storage/innobase/buf/buf0buf.cc

@@ -1396,7 +1396,7 @@ pfs_register_buffer_block(
 			: NULL;
 
 #   ifdef UNIV_DEBUG
-		rwlock = &block->debug_latch;
+		rwlock = block->debug_latch;
 		ut_a(!rwlock->pfs_psi);
 		rwlock->pfs_psi = (PSI_server)
 			? PSI_server->init_rwlock(buf_block_debug_latch_key,
@@ -1458,6 +1458,7 @@ buf_block_init(
 	page_zip_des_init(&block->page.zip);
 
 	mutex_create(LATCH_ID_BUF_BLOCK_MUTEX, &block->mutex);
+	ut_d(block->debug_latch = UT_NEW_NOKEY(rw_lock_t()));
 
 #if defined PFS_SKIP_BUFFER_MUTEX_RWLOCK || defined PFS_GROUP_BUFFER_SYNC
 	/* If PFS_SKIP_BUFFER_MUTEX_RWLOCK is defined, skip registration
@@ -1469,7 +1470,7 @@ buf_block_init(
 
 	rw_lock_create(PFS_NOT_INSTRUMENTED, &block->lock, SYNC_LEVEL_VARYING);
 
-	ut_d(rw_lock_create(PFS_NOT_INSTRUMENTED, &block->debug_latch,
+	ut_d(rw_lock_create(PFS_NOT_INSTRUMENTED, block->debug_latch,
 			    SYNC_LEVEL_VARYING));
 
 #else /* PFS_SKIP_BUFFER_MUTEX_RWLOCK || PFS_GROUP_BUFFER_SYNC */
@@ -1477,7 +1478,7 @@ buf_block_init(
 	rw_lock_create(buf_block_lock_key, &block->lock, SYNC_LEVEL_VARYING);
 
 	ut_d(rw_lock_create(buf_block_debug_latch_key,
-			    &block->debug_latch, SYNC_LEVEL_VARYING));
+			    block->debug_latch, SYNC_LEVEL_VARYING));
 
 #endif /* PFS_SKIP_BUFFER_MUTEX_RWLOCK || PFS_GROUP_BUFFER_SYNC */
 
@@ -1736,6 +1737,18 @@ buf_pool_set_sizes(void)
 	buf_pool_mutex_exit_all();
 }
 
+/** Free the synchronization objects of a buffer pool block descriptor
+@param[in,out]	block	buffer pool block descriptor */
+static void buf_block_free_mutexes(buf_block_t* block)
+{
+	mutex_free(&block->mutex);
+	rw_lock_free(&block->lock);
+	ut_d(rw_lock_free(block->debug_latch));
+	ut_ad(!block->debug_latch->magic_n);
+	ut_d(block->debug_latch->magic_n = RW_LOCK_MAGIC_N);
+	ut_d(UT_DELETE(block->debug_latch));
+}
+
 /********************************************************************//**
 Initialize a buffer pool instance.
 @return DB_SUCCESS if all goes well. */
@@ -1799,11 +1812,7 @@ buf_pool_init_instance(
 					buf_block_t*	block = chunk->blocks;
 
 					for (i = chunk->size; i--; block++) {
-						mutex_free(&block->mutex);
-						rw_lock_free(&block->lock);
-
-						ut_d(rw_lock_free(
-							&block->debug_latch));
+						buf_block_free_mutexes(block);
 					}
 
 					buf_pool->allocator.deallocate_large(
@@ -1949,10 +1958,7 @@ buf_pool_free_instance(
 		buf_block_t*	block = chunk->blocks;
 
 		for (ulint i = chunk->size; i--; block++) {
-			mutex_free(&block->mutex);
-			rw_lock_free(&block->lock);
-
-			ut_d(rw_lock_free(&block->debug_latch));
+			buf_block_free_mutexes(block);
 		}
 
 		buf_pool->allocator.deallocate_large(
@@ -2826,11 +2832,7 @@ buf_pool_resize()
 
 				for (ulint j = chunk->size;
 				     j--; block++) {
-					mutex_free(&block->mutex);
-					rw_lock_free(&block->lock);
-
-					ut_d(rw_lock_free(
-						&block->debug_latch));
+					buf_block_free_mutexes(block);
 				}
 
 				buf_pool->allocator.deallocate_large(
@@ -4750,7 +4752,7 @@ buf_page_get_gen(
 	if (!fsp_is_system_temporary(page_id.space())) {
 		ibool   ret;
 		ret = rw_lock_s_lock_nowait(
-			&fix_block->debug_latch, file, line);
+			fix_block->debug_latch, file, line);
 		ut_a(ret);
 	}
 #endif /* UNIV_DEBUG */

storage/innobase/gis/gis0sea.cc

@@ -1567,8 +1567,7 @@ rtr_copy_buf(
 	matches->block.curr_left_side = block->curr_left_side;
 	matches->block.index = block->index;
 #endif /* BTR_CUR_HASH_ADAPT */
-	ut_d(memcpy(&matches->block.debug_latch, &block->debug_latch,
-		    sizeof(rw_lock_t)));
+	ut_d(matches->block.debug_latch = NULL);
 }
 
 /****************************************************************//**

storage/innobase/include/buf0buf.h

@@ -1797,7 +1797,7 @@ struct buf_block_t{
 # ifdef UNIV_DEBUG
 	/** @name Debug fields */
 	/* @{ */
-	rw_lock_t	debug_latch;	/*!< in the debug version, each thread
+	rw_lock_t*	debug_latch;	/*!< in the debug version, each thread
 					which bufferfixes the block acquires
 					an s-latch here; so we can use the
 					debug utilities in sync0rw */

storage/innobase/include/buf0buf.ic

@@ -985,7 +985,7 @@ buf_block_buf_fix_inc_func(
 	threaded. */
 	if (!fsp_is_system_temporary(block->page.id.space())) {
 		ibool   ret;
-		ret = rw_lock_s_lock_nowait(&block->debug_latch, file, line);
+		ret = rw_lock_s_lock_nowait(block->debug_latch, file, line);
 		ut_a(ret);
 	}
 #endif /* UNIV_DEBUG */
@@ -1033,7 +1033,7 @@ buf_block_buf_fix_dec(
 	Debug latch is not of much help if access to block is single
 	threaded. */
 	if (!fsp_is_system_temporary(block->page.id.space())) {
-		rw_lock_s_unlock(&block->debug_latch);
+		rw_lock_s_unlock(block->debug_latch);
 	}
 #endif /* UNIV_DEBUG */
 }
@@ -1276,7 +1276,7 @@ buf_page_release_zip(
 		is single threaded. */
 		buf_block_t*	block = reinterpret_cast<buf_block_t*>(bpage);
 		if (!fsp_is_system_temporary(block->page.id.space())) {
-			rw_lock_s_unlock(&block->debug_latch);
+			rw_lock_s_unlock(block->debug_latch);
 		}
 	}
 #endif /* UNIV_DEBUG */
@@ -1312,7 +1312,7 @@ buf_page_release_latch(
 	temporary. Debug latch is not of much help if access to block
 	is single threaded. */
 	if (!fsp_is_system_temporary(block->page.id.space())) {
-		rw_lock_s_unlock(&block->debug_latch);
+		rw_lock_s_unlock(block->debug_latch);
 	}
 #endif /* UNIV_DEBUG */