lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Thu, 05 Dec 2013 07:05:52 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] net: introduce dev_consume_skb_any()

On Thu, 2013-12-05 at 06:45 -0800, Eric Dumazet wrote:
> On Thu, 2013-12-05 at 15:13 +0100, Hannes Frederic Sowa wrote:
> > On Thu, Dec 05, 2013 at 04:45:08AM -0800, Eric Dumazet wrote:
> > > -		local_irq_save(flags);
> > > -		sd = &__get_cpu_var(softnet_data);
> > > -		skb->next = sd->completion_queue;
> > > -		sd->completion_queue = skb;
> > > -		raise_softirq_irqoff(NET_TX_SOFTIRQ);
> > > -		local_irq_restore(flags);
> > > +	if (likely(atomic_read(&skb->users) == 1)) {
> > > +		smp_rmb();
> > 
> > Could you give me a hint why this barrier is needed? IMHO the volatile
> > access in atomic_read should get rid of the control dependency so I
> > don't see a need for this barrier. Without the volatile access a
> > compiler-barrier would still suffice, I guess?
> 
> Please take a look at kfree_skb() implementation.
> 
> If you think a comment is needed there, please feel free to add it.
> 

My understanding of this (old) barrier here is an implicit wmb in
skb_get()

This probably needs something like :

static inline struct sk_buff *skb_get(struct sk_buff *skb)
{
	smp_mb__before_atomic_inc(); /* check {consume|kfree}_skb() */
	atomic_inc(&skb->users);
}



--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Powered by blists - more mailing lists