[bug report] ksm: introduce ksm_max_page_sharing per page deduplication limit

[Dan Carpenter <dan.carpenter@oracle.com>]

Hello Andrea Arcangeli,

The patch 1073fbb7013b: "ksm: introduce ksm_max_page_sharing per page
deduplication limit" from May 13, 2017, leads to the following static
checker warning:

	mm/ksm.c:1442 __stable_node_chain()
	warn: 'stable_node' was already freed.

mm/ksm.c
  1433  static struct stable_node *__stable_node_chain(struct stable_node **_stable_node,
  1434                                                 struct page **tree_page,
  1435                                                 struct rb_root *root,
  1436                                                 bool prune_stale_stable_nodes)
  1437  {
  1438          struct stable_node *stable_node = *_stable_node;
  1439          if (!is_stable_node_chain(stable_node)) {
  1440                  if (is_page_sharing_candidate(stable_node)) {
  1441                          *tree_page = get_ksm_page(stable_node, false);
  1442                          return stable_node;

There is a comment about this somewhere down the call tree but if
get_ksm_page() fails then we're returning a freed pointer here which is
gnarly.

  1443                  }
  1444                  return NULL;
  1445          }
  1446          return stable_node_dup(_stable_node, tree_page, root,
  1447                                 prune_stale_stable_nodes);
  1448  }


regards,
dan carpenter

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