Re: [Xen-devel] xenstore ring overflow when too many watches are fired

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 08/10/2009 12:01, "James Harper" <james.harper@xxxxxxxxxxxxxxxx> wrote:

> A bug has been discovered in GPLPV that causes duplicate watches to be
> added when Windows resumes from a hibernate. I'm not completely sure at
> this point, but it appears that the firing of that many watches causes
> dom0 to overwrite data on the ring.
> 
> Are there any protections in xenstored (which does the writing I think)
> against xenstore ring overflow caused by a large number (>23 I think) of
> watches firing in unison? I can't see any...
> 
> Obviously I'll fix the GPLPV bug too, but it would be nice to know that
> too many watches wouldn't break xenstore.

Messages (whether replies or watch notifications) get stored on a
per-connection linked list and trickled onto the shared ring as space
becomes available. It shouldn't be possible for the ring to overflow and eat
its own tail.

 -- Keir



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