Re: [PATCH net-next v2 1/9] xen-netback: Introduce TX grant map definitions

[Zoltan Kiss]

On 16/12/13 17:50, Wei Liu wrote:
> On Mon, Dec 16, 2013 at 03:21:40PM +0000, Zoltan Kiss wrote:
> [...]
> > > > > > > Should this be BUG_ON? AIUI this kthread should be the only one doing
> > > > > > > unmap, right?
> > > > > The NAPI instance can do it as well if it is a small packet fits
> > > > > into PKT_PROT_LEN. But still this scenario shouldn't really happen,
> > > > > I was just not sure we have to crash immediately. Maybe handle it as
> > > > > a fatal error and destroy the vif?
> > > It depends. If this is within the trust boundary, i.e. everything at the
> > > stage should have been sanitized then we should BUG_ON because there's
> > > clearly a bug somewhere in the sanitization process, or in the
> > > interaction of various backend routines.
> >
> > My understanding is that crashing should be avoided if we can bail
> > out somehow. At this point there is clearly a bug in netback
> > somewhere, something unmapped that page before it should have
> > happened, or at least that array get corrupted somehow. However
> > there is a chance that xenvif_fatal_tx_err() can contain the issue,
> > and the rest of the system can go unaffected.
>
> That would make debugging much harder if a crash is caused by a previous
> corrupted array and we pretend we can carry on serving IMHO. Now netback
> is having three routines (NAPI, two kthreads) to serve a single vif, the
> interation among them makes bug hard to reproduce.

OK, I'll make this a BUG() in the next series.

Zoli

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