On Tue, 10 Nov 2015 19:44:41 +0100 Andrea Arcangeli <aarcange@xxxxxxxxxx> wrote: > The STABLE_NODE_DUP_HEAD must be an unique valid pointer never used > elsewhere in any stable_node->head/node to avoid a clashes with the > stable_node->node.rb_parent_color pointer, and different from > &migrate_nodes. So the second field of &migrate_nodes is picked and > verified as always safe with a BUILD_BUG_ON in case the list_head > implementation changes in the future. > > ... > > + /* > + * We need the second aligned pointer of the migrate_nodes > + * list_head to stay clear from the rb_parent_color union > + * (aligned and different than any node) and also different > + * from &migrate_nodes. This will verify that future list.h changes > + * don't break STABLE_NODE_DUP_HEAD. > + */ > + BUILD_BUG_ON(STABLE_NODE_DUP_HEAD <= &migrate_nodes); > + BUILD_BUG_ON(STABLE_NODE_DUP_HEAD >= &migrate_nodes + 1); mm/ksm.c: In function 'remove_node_from_stable_tree': mm/ksm.c:618: error: call to '__compiletime_assert_618' declared with attribute error: BUILD_BUG_ON failed: STABLE_NODE_DUP_HEAD <= &migrate_nodes mm/ksm.c:619: error: call to '__compiletime_assert_619' declared with attribute error: BUILD_BUG_ON failed: STABLE_NODE_DUP_HEAD >= &migrate_nodes + 1 That's with gcc-4.4.4. I don't have time at present to investigate so I'll switch them to WARN_ON_ONCE for now. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>