Re: Xen 4.7 crash

[Aaron Cornelius <aaron.cornelius@dornerworks.com>]

On 6/9/2016 7:14 AM, Ian Jackson wrote:
> Aaron Cornelius writes ("Re: [Xen-devel] Xen 4.7 crash"):
>> I am not that familiar with the xenstored code, but as far as I can tell
>> the grant mapping will be held by the xenstore until the xs_release()
>> function is called (which is not called by libxl, and I do not
>> explicitly call it in my software, although I might now just to be
>> safe), or until the last reference to a domain is released and the
>> registered destructor (destroy_domain), set by talloc_set_destructor(),
>> is called.
>
> I'm not sure I follow.  Or maybe I disagree.  ISTM that:
>
> The grant mapping is released by destroy_domain, which is called via
> the talloc destructor as a result of talloc_free(domain->conn) in
> domain_cleanup.  I don't see other references to domain->conn.
>
> domain_cleanup calls talloc_free on domain->conn when it sees the
> domain marked as dying in domain_cleanup.
>
> So I still think that your acl reference ought not to keep the grant
> mapping alive.

It took a while to complete the testing, but we've finished trying to 
reproduce the error using oxenstored instead of the C xenstored.  When 
the condition occurs that caused the error with the C xenstored (on 
4.7.0-rc4/8478c9409a2c6726208e8dbc9f3e455b76725a33), oxenstored does not 
cause the crash.

So for whatever reason, it would appear that the C xenstored does keep 
the grant allocations open, but oxenstored does not.

- Aaron Cornelius


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