Re: [Xen-devel] Fatal crash on xen4.2 HVM + qemu-xen dm + NFS

[Alex Bligh <alex@xxxxxxxxxxx>]

Stefano,

--On 16 January 2013 17:33:59 +0000 Stefano Stabellini 
<stefano.stabellini@xxxxxxxxxxxxx> wrote:
> Almost. I am saying that the kernel completed the AIO write and notified
> QEMU after it received an ACK from the other end, but before the
> tcp_retransmit was supposed to run.  I admit I am not that familiar with
> the network stack so this is just a supposition.
OK, let's presume you are right here.

The page is still referenced by the networking stack at this point
because it's in some tcp transmit buffer (the original thread
established that), and that will show up in a reference count.

Surely before Xen removes the grant on the page, unmapping it from dom0's
memory, it should check to see if there are any existing references
to the page and if there are, given the kernel its own COW copy, rather
than unmap it totally which is going to lead to problems.

--
Alex Bligh

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