[Xen-devel] Re: mem_sharing: summarized problems when domain is dying

[Jui-Hao Chiang <juihaochiang@xxxxxxxxx>]

Hi

On Fri, Jan 21, 2011 at 11:19 AM, Jui-Hao Chiang <juihaochiang@xxxxxxxxx> wrote:
> Hi, Tim:
>
> From tinnycloud's result, here I summarize the current problem and
> findings of mem_sharing due to domain dying.
> (1) When domain is dying, alloc_domheap_page() and
> set_shared_p2m_entry() would just fail. So the shr_lock is not enough
> to ensure that the domain won't die in the middle of mem_sharing code.
> As tinnycloud's code shows, is that better to use
> rcu_lock_domain_by_id before calling the above two functions?
>

There seems no good locking to protect a domain from changing the
is_dying state. So the unshare function could fail in the middle in
several points, e.g., alloc_domheap_page and set_shared_p2m_entry.
If that's the case, we need to add some checking, and probably revert
the things we have done when is_dying is changed in the middle.

Any comments?

Jui-Hao

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