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Re: [Xen-devel] [PATCH] x86: fix domain cleanup

  • To: Jan Beulich <jbeulich@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
  • Date: Tue, 28 Oct 2008 09:36:36 +0000
  • Cc:
  • Delivery-date: Tue, 28 Oct 2008 02:37:08 -0700
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: Ack44Kug6nDi2KTTEd2LtwAWy6hiGQ==
  • Thread-topic: [Xen-devel] [PATCH] x86: fix domain cleanup

On 28/10/08 09:26, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

> But how would one distinguish the two (or three at present, due to

I'm not sure. Do they need to be distinguished?

> Also, where is the
> matching put_page() for the type refcount decrement in free_page_type()
> in the circular case (in  free_page_type(A) -> put_page_and_type(B) ->
> free_page_type(B) -> put_page_and_type(A) we'll have the type refcount
> decremented twice, but the page refcount just once)? Or is this decrement
> invalid in that case (I don't think it is, as get_lN_linear_pagetable()
> increments it along with keeping the page reference it obtained in the
> success case, but if it is, it again poses the question of how to recognize
> that case)?

Ah, looks like it's been broken since the preemptible page_type patch went
in. Perhaps the tail of free_page_type() should go into __put_page_type(),
as it's not needed by the call site in relinquish_memory(): the caller
doesn't really hold a type reference to be dropped; and the logic for being
preempted doesn't apply since relinquish_memory() requests no preemption.

 -- Keir

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