Subject: Re: Problem with dev_kfree_skb_any() in 2.6.0

From: Jeff Garzik <[email-masked]>
Date: Thu, 1 Jan 2004 21:58:07 -0500

On Thu, Jan 01, 2004 at 12:42:18PM -0800, David S. Miller wrote:
> On Tue, 30 Dec 2003 12:43:21 -0500
> Jeff Garzik <[email-masked]> wrote:
> 
> > Luckily, I feel there is an easy solution, as shown in the attached 
> > patch.  We _already_ queue skbs in dev_kfree_skb_irq().  Therefore, 
> > dev_kfree_skb_any() can simply use precisely that same solution.  The 
> > raise-softirq code will immediately proceed to action if we are not in 
> > hard IRQ context, otherwise it will follow the expected path.
> 
> Ok, this is reasonable and works.
> 
> Though, is there any particular reason you don't like adding a
> "|| irqs_disabled()" check to the if statement instead?
> I prefer that solution better actually.

Yep, in fact when I wrote the above message, I came across a couple when I
was pondering...
* the destructor runs in a more predictable context.
* given the problem that started this thread, the 'if' test is a
  potentially problematic area.  Why not eliminate all possibility that
  this problem will occur again?

The only counter argument to this -- to which I have no data to answer --
is that there may be advantage to calling __kfree_skb immediately
instead of deferring it slightly.  I didn't think that disadvantage
outweighted the above, but who knows...  I can possibly be convinced
otherwise.  (and "otherwise" would be using || irqs_disabled())

For the users who don't know/don't care about their context, it just
seemed to me that they were not a hot path like users of dev_kfree_skb()
and dev_kfree_skb_irq() [unconditional] are...

	Jeff