Messages in this thread | | | Subject | Re: lockdep trace from posix timers | From | Peter Zijlstra <> | Date | Mon, 20 Aug 2012 17:56:51 +0200 |
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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?
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