On Tue 05-11-13 02:05:44, Cody P Schafer wrote: > On 11/04/2013 05:40 PM, Cody P Schafer wrote: > > Provide a new helper called rb_next_postorder_entry() to perform NULL > > checks and container_of() coversions and use it in > > rbtree_for_each_entry_safe() to fix oopses that occur when rb_node is > > not the first element in the entry. > > On second thought, it appears I was a bit to hasty with this, and this patch actually breaks things. > > On 11/04/2013 04:45 PM, Jan Kara wrote:> On Mon 04-11-13 15:26:38, Jan Kara wrote: > >> On Fri 01-11-13 15:38:50, Cody P Schafer wrote: > >>> Use rbtree_postorder_for_each_entry_safe() to destroy the rbtree instead > >>> of opencoding an alternate postorder iteration that modifies the tree > >> Thanks. I've merged the patch into my tree. > > Hum, except that the kernel oopses with this patch. And I think the > > problem is in rbtree_postorder_for_each_entry_safe(). How are those tests > > for NULL supposed to work? For example if the tree is empty, 'pos' will be > > NULL and you'll call rb_next_postorder(&NULL->field) which is pretty much > > guaranteed to oops if 'field' doesn't have offset 0 in the structure... > > No, it shouldn't oops because pos won't be NULL, &pos->field will be. > > pos is only assigned via an rb_entry(rb_first_postorder()) or > rb_entry(rb_next_postorder()). rb_next_postorder() and > rb_first_postorder() can return NULL. That NULL then is munged by > rb_entry to be (NULL - offset_of_field). Causing (&pos->field == NULL == > (pos + offset_of_field)). OK, so I had a second look. And the compiler thinks differently than you :) The thing is that my gcc (4.3.4) apparently assumes pointer underflow is undefined and thus optimizes your test &pos->field to 1. I've asked our gcc guys for a definitive answer but clearly your code will need some way to avoid pointer underflows... Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
