On Mon, 2012-08-20 at 17:41 +0200, Oleg Nesterov wrote: > I won't insist. The patch I sent uses PF_EXITING and the fake > "struct callback_head* TWORK_EXITED", but this looks almost the same.
Right, I used a fake callback_head because it avoided a few special cases since its a dereferencable pointer. > > > Note also your patch breaks fifo, but this is fixable. > > > > Why do you care about the order? > > IMHO, this is just more natural. Depends on what you're used to I guess ;-) Both RCU and irq_work are filo, this seems to be the natural way for single linked lists. > For example. keyctl_session_to_parent() does _cancel only to protect > from exploits doing keyctl(KEYCTL_SESSION_TO_PARENT) in an endless > loop. It could simply do task_work_add(), but in this case we need > fifo for correctness. I'm not entirely sure I see, not doing the cancel would delay the free until the executing of key_change_session_keyring()? doing that keyctl() in an indefinite loop involves going back to userspace, so where's the resource issue? Also, I'm not seeing where the FIFO requirement comes from. > > Iterating a single linked queue in fifo > > seems more expensive than useful. > > Currently the list is fifo (we add to the last element), this is O(1). depends on what way you look at the list I guess, with a single linked list there's only one end you can add to in O(1), so we're calling that the tail? > But the list should be short, we can reverse it in _run() if we change > task_work_add() to add to the head. Reversing a (single linked) list is O(n^2).. which is indeed doable for short lists, but why assume its short? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/