Paul E. McKenney a écrit :

On Thu, Oct 30, 2008 at 12:30:20PM +0100, Eric Dumazet wrote:

quoted

-		while (udp_lib_lport_inuse(net, snum, udptable, sk,
-					   saddr_comp)) {
+		for (;;) {
+			hslot = &udptable->hash[udp_hashfn(net, snum)];
+			spin_lock_bh(&hslot->lock);
+			if (!udp_lib_lport_inuse(net, snum, hslot, sk, saddr_comp))
+				break;
+			spin_unlock_bh(&hslot->lock);
 			do {
 				snum = snum + rand;
 			} while (snum < low || snum > high);

The above -really- confuses me, but not part of this patch.  If we are
out of range, keep going?  Well, I guess that since it is a short, we
cannot go very far...

quoted

 			if (snum == first)
 				goto fail;

And I don't understand how we are guaranteed to have scanned all the
possible ports upon failure, but happy to leave that to you guys.

Well, we have 65536(=2^16) possible port values, and while 'rand' is random,
it has the interesting property/bias of being odd.

We know (thanks modular arithmetic / congruence relation) we will hit
all 65356 values exactly once, after exactly 65536 iterations.