[email protected] writes:
> From: wenxu <[email protected]>
>
> In case almost or all available ports are taken, clash resolution can
> take a very long time, resulting in soft lockup.
>
> This can happen when many to-be-natted hosts connect to same
> destination:port (e.g. a proxy) and all connections pass the same SNAT.
>
> Pick a random offset in the acceptable range, then try ever smaller
> number of adjacent port numbers, until either the limit is reached or a
> useable port was found. This results in at most 248 attempts
> (128 + 64 + 32 + 16 + 8, i.e. 4 restarts with new search offset)
> instead of 64000+.
>
> Signed-off-by: wenxu <[email protected]>
> ---
> lib/conntrack.c | 29 +++++++++++++++++++++++++----
> 1 file changed, 25 insertions(+), 4 deletions(-)
>
> diff --git a/lib/conntrack.c b/lib/conntrack.c
> index ac95d0f..a776e57 100644
> --- a/lib/conntrack.c
> +++ b/lib/conntrack.c
> @@ -2359,16 +2359,37 @@ nat_get_unique_l4(struct conntrack *ct, struct conn
> *nat_conn,
> ovs_be16 *port, uint16_t curr, uint16_t min,
> uint16_t max)
> {
> + static const unsigned int max_attempts = 128;
> + uint16_t range = max - min + 1;
> + unsigned int attempts;
> uint16_t orig = curr;
> + unsigned int i = 0;
>
> + attempts = range;
> + if (attempts > max_attempts) {
> + attempts = max_attempts;
> + }
> +
> +another_round:
> + i = 0;
> FOR_EACH_PORT_IN_RANGE (curr, min, max) {
> - *port = htons(curr);
> - if (!conn_lookup(ct, &nat_conn->rev_key,
> - time_msec(), NULL, NULL)) {
> - return true;
can't we rewrite this as:
if (i++ >= attempts) {
break;
}
...
I find it a bit more readable in this case.
> + if (i++ < attempts) {
> + *port = htons(curr);
> + if (!conn_lookup(ct, &nat_conn->rev_key,
> + time_msec(), NULL, NULL)) {
> + return true;
> + }
> + } else {
> + break;
> }
> }
>
> + if (attempts < range && attempts >= 16) {
> + attempts /= 2;
> + curr = min + (random_uint32() % range);
> + goto another_round;
> + }
> +
> *port = htons(orig);
>
> return false;
> --
> 1.8.3.1
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