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From: "Michael S. Tsirkin" <mst@redhat.com>
To: netdev@vger.kernel.org, Herbert Xu <herbert@gondor.hengli.com.au>
Subject: skb_linearize
Date: Sun, 16 Sep 2012 12:17:47 +0300	[thread overview]
Message-ID: <20120916091747.GA23775@redhat.com> (raw)

I notice that dev_hard_start_xmit might invoke
__skb_linearize e.g. if device does not support NETIF_F_SG.

This in turn onvokes __pskb_pull_tail, and
documentation of __pskb_pull_tail says:
  &sk_buff MUST have reference count of 1.

I am guessing 'reference count' means users in this context, right?
IIUC this is because it modifies skb in a way that
isn't safe if anyone else is looking at the skb.


However, I don't see what guarantees that reference
count is 1 when dev_hard_start_xmit invokes
linearize. In particular it calls dev_queue_xmit_nit
which could queue packets on a network tap.

Could someone help me understand please?

Thanks!

-- 
MST

             reply	other threads:[~2012-09-16  9:16 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-09-16  9:17 Michael S. Tsirkin [this message]
2012-09-16 15:07 ` skb_linearize Ben Hutchings
2012-10-31 19:15   ` skb_linearize Michael S. Tsirkin
2012-10-31 21:03     ` skb_linearize Ben Hutchings

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