Re: [Xen-devel] netback BUG_ON when using copy_skb=1

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 17.10.13 at 09:41, jerry <jerry.lilijun@xxxxxxxxxx> wrote:
> But there may be still concurrency problems in my test.
> If the page replacing in copy_pending_req() was done after 
> netif_get_page_ext() in netbk_gop_frag(), copy_gop->flags is wrongly marked 
> with GNTCOPY_source_gref.
> Here the memory of that page in skb has been replaced with Dom0 local 
> memory, so the later HYPERVISOR_multicall() with GNTTABOP_copy in 
> netbk_rx_actions() will get errors.
> The messages is shown as:
> 
> (XEN) grant_table.c:305:d0 Bad flags (0) or dom (0). (expected dom 0)
> 
> Would you like to share some opinions?

At a first glance that seems possible, but the question is - does it
cause any problems other than the quoted message to be issued
(and the problematic packet getting re-transmitted)? I'm asking
mainly because fixing this would appear to imply adding locking to
these paths - with the risk of adversely affecting performance.

Jan


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