Le jeudi 26 mai 2011 à 21:11 -0700, Ben Greear a écrit :

On 05/26/2011 08:42 PM, Eric Dumazet wrote:

quoted

Le jeudi 26 mai 2011 à 16:55 -0700, greearb@candelatech.com a écrit :

quoted

quoted

  out_free:
  	kfree_skb(skb);
  out_unlock:
-	if (dev)
+	if (dev&&  need_rls_dev)
  		dev_put(dev);
  out:
  	return err;

Hmmm, I wonder why you want this Ben.

IMHO this is buggy, because we can sleep in this function.

We must take a ref on device (its really cheap these days, now we have a
percpu device refcnt)

Why must you take the reference?  And if we must, why isn't the
current code that assigns the prot_hook.dev without taking a
reference OK?

If we sleep, device can disappear under us.

The only way to not take a reference is to hold rcu_read_lock(), but
you're not allowed to sleep under rcu_read_lock().

It seems a waste to do the lookup and free if we don't have to,
and with thousands of devices, the lookup might take a reasonable
amount of effort?

I understand you want to avoid the lookup, this part is fine for me, but
you need to take a reference on the device before eventual sleep.

Nowadays its a single "inc" instruction on x86, without even a lock
prefix (this on a percpu integer)