netdev - Re: [net-next PATCH] net: codel: Avoid undefined behavior from signed overflow

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Date:	Thu, 31 Oct 2013 08:10:41 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jesper Dangaard Brouer <jbrouer@...hat.com>
Cc:	Jesper Dangaard Brouer <brouer@...hat.com>, netdev@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Dave Taht <dave.taht@...il.com>
Subject: Re: [net-next PATCH] net: codel: Avoid undefined behavior from
 signed overflow

On Thu, 2013-10-31 at 15:15 +0100, Jesper Dangaard Brouer wrote:

> Okay, I'll cook up another patch, after work.
> 
> Adding all the typecheck() stuff, just bloats the code.
> 
> Would it be better/okay just to do?:
>  (s32)((u32)(a) - (u32)(b)) > 0)
> 
> 

What about using the existing codel types ?

diff --git a/include/net/codel.h b/include/net/codel.h
index 389cf62..89a7781 100644
--- a/include/net/codel.h
+++ b/include/net/codel.h
@@ -72,7 +72,12 @@ static inline codel_time_t codel_get_time(void)
 	return ns >> CODEL_SHIFT;
 }
 
-#define codel_time_after(a, b)		((s32)(a) - (s32)(b) > 0)
+static inline bool codel_time_after(codel_time_t a, codel_time_t b)
+{
+	codel_tdiff_t delta = a - b;
+
+	return delta >= 0;
+}
 #define codel_time_after_eq(a, b)	((s32)(a) - (s32)(b) >= 0)
 #define codel_time_before(a, b)		((s32)(a) - (s32)(b) < 0)
 #define codel_time_before_eq(a, b)	((s32)(a) - (s32)(b) <= 0)


You need of course something similar for all variants.


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