Re: [Xen-devel] netback Oops then xenwatch stuck in D state

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, 2013-02-14 at 12:20 +0000, David Vrabel wrote:
> On 14/02/13 11:48, Jan Beulich wrote:
> >>>> On 14.02.13 at 12:20, Wei Liu <wei.liu2@xxxxxxxxxx> wrote:
> > 
> >> If this is a bug, and, if my previous patch fixes Christopher's OOPS, he
> >> will hit this bug soon when shutting down DomU.
> > 
> > I don't think this patch will fix his problems, which - as described
> > yesterday - I'm relatively certain result from the harsh action
> > netbk_fatal_tx_err() does.
> 
> I can't see anything broken in netbk_fatal_tx_err().
> 
> However, a call to netbk_fatal_tx_err() may result in the vif's ref
> count going to 1 which means a simutaneous attempt to shutdown the vif
> will free the net device.

> Netback thread              Xenwatch thread
> 
> netbk_fatal_tx_err()        netback_remove()
>                               xenvif_disconnect()
>                                 ...
>                                 free_netdev()
> netbk_tx_err() Oops!
> 

This is not a problem. Reading comments and code of the commit,
netbk_fatal_tx_err shuts down the vif entirely (at the moment the timer
is not handled though) which should make sure it will never get
scheduled again, so in practice it will never hit netbk_tx_err.


Wei.

> David



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