Re: [Xen-devel] [PATCHv5 12/14] xen-blkback: safely unmap grants in case they are still in use

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 09/03/15 09:09, Bob Liu wrote:
> Hi David,
> 
> Recently I met an issue which is likely related with this patch. It
> happened when running block benchmark on domU, the backend was an iSCSI
> disk connected to dom0. I got below panic at put_page_testzero() on
> dom0, at that time the ixgbe network card was freeing skb pages in
> __skb_frag_unref() but the page->_count was already 0.
> Do you think is it possiable that page was already freed by blkback?

It's possible, but in this case I think the blkback device must have
been destroyed for this to have happened,  because blkback doesn't free
the pages until it is destroyed.

But in general networked block storage isn't safe without this patch.

David

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