From 1ba3aab3033b464f352659720824d7124c21dbf9 Mon Sep 17 00:00:00 2001 From: Jesper Dangaard Brouer Date: Thu, 31 Oct 2013 22:10:55 +0100 Subject: [PATCH] net: codel: Avoid undefined behavior from signed overflow As described in commit 5a581b367 (jiffies: Avoid undefined behavior from signed overflow), according to the C standard 3.4.3p3, overflow of a signed integer results in undefined behavior. To fix this, do as the above commit, and do an unsigned subtraction, and interpreting the result as a signed two's-complement number. This is based on the theory from RFC 1982 and is nicely described in wikipedia here: https://en.wikipedia.org/wiki/Serial_number_arithmetic#General_Solution A side-note, I have seen practical issues with the previous logic when dealing with 16-bit, on a 64-bit machine (gcc version 4.4.5). This were 32-bit, which I have not observed issues with. Cc: Paul E. McKenney Signed-off-by: Jesper Dangaard Brouer Acked-by: Paul E. McKenney Signed-off-by: David S. Miller --- Reading git-format-patch failed