linux-kernel - [32/84] xen/io/ring.h: new macro to detect whether there are too many requests on the ring

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Message-ID: <lsq.1375276989.587143021@decadent.org.uk>
Date:	Wed, 31 Jul 2013 15:23:09 +0200
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>,
	"Jan Beulich" <jbeulich@...e.com>
Subject: [32/84] xen/io/ring.h: new macro to detect whether there are too
 many requests on the ring

3.2.50-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jan Beulich <jbeulich@...e.com>

commit 8d9256906a97c24e97e016482b9be06ea2532b05 upstream.

Backends may need to protect themselves against an insane number of
produced requests stored by a frontend, in case they iterate over
requests until reaching the req_prod value. There can't be more
requests on the ring than the difference between produced requests
and produced (but possibly not yet published) responses.

This is a more strict alternative to a patch previously posted by
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>.

Signed-off-by: Jan Beulich <jbeulich@...e.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 include/xen/interface/io/ring.h | 5 +++++
 1 file changed, 5 insertions(+)

--- a/include/xen/interface/io/ring.h
+++ b/include/xen/interface/io/ring.h
@@ -188,6 +188,11 @@ struct __name##_back_ring {						\
 #define RING_REQUEST_CONS_OVERFLOW(_r, _cons)				\
     (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r))
 
+/* Ill-behaved frontend determination: Can there be this many requests? */
+#define RING_REQUEST_PROD_OVERFLOW(_r, _prod)               \
+    (((_prod) - (_r)->rsp_prod_pvt) > RING_SIZE(_r))
+
+
 #define RING_PUSH_REQUESTS(_r) do {					\
     wmb(); /* back sees requests /before/ updated producer index */	\
     (_r)->sring->req_prod = (_r)->req_prod_pvt;				\

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