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

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Date:	Mon, 28 Jan 2013 16:18:59 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>
Cc:	"Konrad Rzeszutek Wilk" <konrad@...nel.org>,
	"xen-devel" <xen-devel@...ts.xen.org>,
	<linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH 3/3] xen/blkback: Check for insane
 amounts of request on the ring.

>>> On 28.01.13 at 16:42, Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> wrote:
> On Mon, Jan 28, 2013 at 11:07:46AM +0000, Jan Beulich wrote:
>> >>> On 25.01.13 at 19:43, Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> wrote:
>> > @@ -764,6 +768,9 @@ __do_block_io_op(struct xen_blkif *blkif)
>> >  	rp = blk_rings->common.sring->req_prod;
>> >  	rmb(); /* Ensure we see queued requests up to 'rp'. */
>> >  
>> > +	if (RING_REQUEST_PROD_OVERFLOW(&blk_rings->common, rp, rc))
>> > +		return -EACCES;
>> 
>> Actually I wonder whether we need the new macro at all: It seems
>> to me that using RING_REQUEST_CONS_OVERFLOW(&blk_rings->common, rp)
>> here would achieve the same effect.
> 
> But it would not. The RING_REQUEST_CONS_OVERFLOW only check that the
> non-shared ring entries (rsp_prod and rsp_prod_pvt) are less than
> the size of the ring (32). In other words - they check whether we want
> to process more requests as we still have a back-log of responses to
> deal with.

So did you not notice that here 'rp' (i.e. req_prod) is being passed,
not 'rc'?

Jan

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