MDEV-15053 fixup: MSAN use-of-uninitialized-value

buf_page_init_for_read(): Initialize the output parameter of
buf_buddy_alloc().

storage/innobase/buf/buf0buddy.cc

@@ -431,9 +431,9 @@ buf_buddy_alloc_from(void* buf, ulint i, ulint j)
 	return(buf);
 }
 
-/** Allocate a block.
-@param[in]	i	index of buf_pool.zip_free[] or BUF_BUDDY_SIZES
-@param[out]	lru	whether buf_pool.mutex was temporarily released
+/** Allocate a ROW_FORMAT=COMPRESSED block.
+@param i      index of buf_pool.zip_free[] or BUF_BUDDY_SIZES
+@param lru    assigned to true if buf_pool.mutex was temporarily released
 @return allocated block, never NULL */
 byte *buf_buddy_alloc_low(ulint i, bool *lru)
 {

storage/innobase/buf/buf0rea.cc

@@ -86,7 +86,6 @@ static buf_page_t* buf_page_init_for_read(ulint mode, const page_id_t page_id,
                                           ulint zip_size, bool unzip)
 {
   mtr_t mtr;
-  bool lru= false;
 
   if (mode == BUF_READ_IBUF_PAGES_ONLY)
   {
@@ -169,7 +168,7 @@ static buf_page_t* buf_page_init_for_read(ulint mode, const page_id_t page_id,
       block descriptor has been added to buf_pool.LRU and
       buf_pool.page_hash. */
       block->page.zip.data= static_cast<page_zip_t*>
-        (buf_buddy_alloc(zip_size, &lru));
+        (buf_buddy_alloc(zip_size));
 
       /* To maintain the invariant
       block->in_unzip_LRU_list == block->page.belongs_to_unzip_LRU()
@@ -187,7 +186,7 @@ static buf_page_t* buf_page_init_for_read(ulint mode, const page_id_t page_id,
     control block (bpage), in order to avoid the
     invocation of buf_buddy_relocate_block() on
     uninitialized data. */
-    bool lru;
+    bool lru= false;
     void *data= buf_buddy_alloc(zip_size, &lru);
 
     rw_lock_x_lock(hash_lock);

storage/innobase/include/buf0buddy.h

@@ -50,15 +50,14 @@ buf_buddy_get_slot(ulint size)
 }
 
 /** Allocate a ROW_FORMAT=COMPRESSED block.
-@param[in]	i	index of buf_pool.zip_free[] or BUF_BUDDY_SIZES
-@param[out]	lru	whether buf_pool.mutex was temporarily released
+@param i      index of buf_pool.zip_free[] or BUF_BUDDY_SIZES
+@param lru    assigned to true if buf_pool.mutex was temporarily released
 @return allocated block, never NULL */
 byte *buf_buddy_alloc_low(ulint i, bool *lru) MY_ATTRIBUTE((malloc));
 
 /** Allocate a ROW_FORMAT=COMPRESSED block.
-The caller must not hold buf_pool.mutex.
-@param[in]	size	compressed page size
-@param[out]	lru	whether buf_pool.mutex was temporarily released
+@param size   compressed page size in bytes
+@param lru    assigned to true if buf_pool.mutex was temporarily released
 @return allocated block, never NULL */
 inline byte *buf_buddy_alloc(ulint size, bool *lru= nullptr)
 {