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Re: [Xen-devel] can't create any more pv-on-hvm domains after~38under 3.3-testing

On 03/12/2008 17:02, "Steve Ofsthun" <sofsthun@xxxxxxxxxxxxxxx> wrote:

> We have been investigating a similar sounding bug (hung pages with elevated
> reference counts) that occur when blkback requests are issued over an iSCSI
> backend device.  The block requests appear to be running afoul of the lazy
> copy optimization added for netback.  In this path, foreign pages (assumed to
> be netback pages?) are manipulated specially by the dma layer of the dom0
> network stack.  On return to netback, the page refs are cleaned up.
> In our case, the foreign pages actually originate from blkback, are passed to
> iSCSI for processing, and are abused by the ref manipulation in the dom0
> network stack.  On return to blkback, the page refs are off.  What we haven't
> been able to do yet, is identify the exact circumstances that trigger the
> issue.  We have a fairly elaborate reproducer involving running a pool of
> domains and continuously rebooting them.  Eventually, one domain will hang on
> exit with a stuck page with elevated ref counts.

It'll be nice if James has a sure fire repro scenario then.

 -- Keir

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