branches/zip: Merge revisions 4005:4032 from branches/5.1:

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  r4032 | marko | 2009-01-23 15:43:51 +0200 (Fri, 23 Jan 2009) | 10 lines

  branches/5.1: Merge r4031 from branches/5.0:

  btr_search_drop_page_hash_when_freed(): Check if buf_page_get_gen()
  returns NULL.  The page may have been evicted from the buffer pool
  between buf_page_peek_if_search_hashed() and buf_page_get_gen(),
  because the buffer pool mutex will be released between these two calls.
  (Bug #42279, Issue #160)

  rb://82 approved by Heikki Tuuri
  ------------------------------------------------------------------------

ChangeLog

+2009-01-23	The InnoDB Team
+
+	* btr/btr0sea.c:
+	Fix Bug#42279 Race condition in btr_search_drop_page_hash_when_freed()
+
 2009-01-23	The InnoDB Team
 
 	* include/buf0buf.h, buf/buf0buf.c:

btr/btr0sea.c

@@ -1155,10 +1155,18 @@ btr_search_drop_page_hash_when_freed(
 	block = buf_page_get_gen(space, zip_size, page_no, RW_S_LATCH, NULL,
 				BUF_GET_IF_IN_POOL, __FILE__, __LINE__,
 				&mtr);
+	/* Because the buffer pool mutex was released by
+	buf_page_peek_if_search_hashed(), it is possible that the
+	block was removed from the buffer pool by another thread
+	before buf_page_get_gen() got a chance to acquire the buffer
+	pool mutex again.  Thus, we must check for a NULL return. */
 
-	buf_block_dbg_add_level(block, SYNC_TREE_NODE_FROM_HASH);
+	if (UNIV_LIKELY(block != NULL)) {
 
-	btr_search_drop_page_hash_index(block);
+		buf_block_dbg_add_level(block, SYNC_TREE_NODE_FROM_HASH);
+
+		btr_search_drop_page_hash_index(block);
+	}
 
 	mtr_commit(&mtr);
 }