1ba3aab303
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 <paulmck@linux.vnet.ibm.com>
Signed-off-by: Jesper Dangaard Brouer <netoptimizer@brouer.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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11 KiB