branches/zip: buf_LRU_free_block(): Clarify the function comment.

buf/buf0lru.c

@@ -1287,9 +1287,15 @@ buf_LRU_make_block_old(
 
 /**********************************************************************
 Try to free a block.  If bpage is a descriptor of a compressed-only
-page, the descriptor object will be freed as well.  If this function
-returns BUF_LRU_FREED, it will not temporarily release
-buf_pool_mutex. */
+page, the descriptor object will be freed as well.
+
+NOTE: If this function returns BUF_LRU_FREED, it will not temporarily
+release buf_pool_mutex.  Furthermore, the page frame will no longer be
+accessible via bpage.
+
+The caller must hold buf_pool_mutex and buf_page_get_mutex(bpage) and
+release these two mutexes after the call.  No other
+buf_page_get_mutex() may be held when calling this function. */
 UNIV_INTERN
 enum buf_lru_free_block_status
 buf_LRU_free_block(

include/buf0lru.h

@@ -87,9 +87,15 @@ buf_LRU_insert_zip_clean(
 
 /**********************************************************************
 Try to free a block.  If bpage is a descriptor of a compressed-only
-page, the descriptor object will be freed as well.  If this function
-returns BUF_LRU_FREED, it will not temporarily release
-buf_pool_mutex. */
+page, the descriptor object will be freed as well.
+
+NOTE: If this function returns BUF_LRU_FREED, it will not temporarily
+release buf_pool_mutex.  Furthermore, the page frame will no longer be
+accessible via bpage.
+
+The caller must hold buf_pool_mutex and buf_page_get_mutex(bpage) and
+release these two mutexes after the call.  No other
+buf_page_get_mutex() may be held when calling this function. */
 UNIV_INTERN
 enum buf_lru_free_block_status
 buf_LRU_free_block(