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From: David Miller <davem@davemloft.net>
Subject: Re: [RFC,PATCH] loopback: calls netif_receive_skb() instead of
 netif_rx()
Date: Fri, 28 Mar 2008 18:36:52 -0700 (PDT)
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From: Eric Dumazet <dada1@cosmosbay.com>
Date: Sun, 23 Mar 2008 19:48:29 +0100

> [PATCH] loopback: calls netif_receive_skb() instead of netif_rx()

Hmmm...

+static int enough_stack_space(void)
+{
+#ifdef CONFIG_STACK_GROWSUP
+	return 0;
+#else
+	unsigned long free = (unsigned long)&free -
+			     (unsigned long)end_of_stack(current);
+	return free >= THREAD_SIZE/3 ;
+#endif
+}
+

This will always fail when we are on an interrupt stack,
I think you'd want it to succeed in such a case.

Can you agree that, at least to a point, this is getting a bit
convoluted and perhaps adding more complexity than this optimization
deserves? :-)