linux-kernel - Re: [Xen-devel] [PATCH 3/3] xen/blkback: Check for insane amounts of request on the ring.

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Message-ID: <20130128154450.GG4838@konrad-lan.dumpdata.com>
Date:	Mon, 28 Jan 2013 10:44:50 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	David Vrabel <david.vrabel@...rix.com>
Cc:	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
	Konrad Rzeszutek Wilk <konrad@...nel.org>,
	stable@...r.kernel.org
Subject: Re: [Xen-devel] [PATCH 3/3] xen/blkback: Check for insane amounts of
 request on the ring.

On Mon, Jan 28, 2013 at 11:38:50AM +0000, David Vrabel wrote:
> On 25/01/13 18:43, Konrad Rzeszutek Wilk wrote:
> > 
> > Check that the ring does not have an insane amount of requests
> > (more than there could fit on the ring).
> [...]
> > --- a/drivers/block/xen-blkback/blkback.c
> > +++ b/drivers/block/xen-blkback/blkback.c
> [...]
> > @@ -415,8 +415,12 @@ int xen_blkif_schedule(void *arg)
> >  		blkif->waiting_reqs = 0;
> >  		smp_mb(); /* clear flag *before* checking for work */
> >  
> > -		if (do_block_io_op(blkif))
> > +		rc = do_block_io_op(blkif);
> > +		if (rc > 0)
> >  			blkif->waiting_reqs = 1;
> > +		if (rc == -EACCES)
> > +			wait_event_interruptible(blkif->shutdown_wq,
> > +						 kthread_should_stop());
> 
> So if this happens then the backend silently stops processing any
> further requests?  I think it should print an error and disconnect from
> the front end.

I was not sure what it should print?

"Frontend provided bogus ring requests. Halting ring processing"?

It does eventually disconnect from the front-end as the XenBus enters
the Disconnect phase. It seemed the strike the balance - so that if
the frontend negotiates again the ring can start again and penalize
the frontend for giving bogus data.

> 
> David
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