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Message-ID: <1370486101.31875.10.camel@cr0>
Date: Thu, 06 Jun 2013 10:35:01 +0800
From: Cong Wang <amwang@...hat.com>
To: David Miller <davem@...emloft.net>
Cc: netdev@...r.kernel.org, dingtianhong@...wei.com,
yoshfuji@...ux-ipv6.org
Subject: Re: [Patch net] ipv6,mcast: always hold idev->lock before mca_lock
On Sat, 2013-05-11 at 16:11 -0700, David Miller wrote:
> From: Cong Wang <amwang@...hat.com>
> Date: Wed, 8 May 2013 15:41:54 +0800
>
> > @@ -1369,7 +1370,7 @@ static struct sk_buff *mld_newpack(struct net_device *dev, int size)
> >
> > skb_reserve(skb, hlen);
> >
> > - if (ipv6_get_lladdr(dev, &addr_buf, IFA_F_TENTATIVE)) {
> > + if (__ipv6_get_lladdr(idev, &addr_buf, IFA_F_TENTATIVE)) {
> > /* <draft-ietf-magma-mld-source-05.txt>:
> > * use unspecified address as the source address
> > * when a valid link-local address is not available.
>
> You aren't necessarily going to be holding idev->lock, therefore you can't
> just do a lockless traversal of idev->addr_list here.
>
> Yes, you can elide the rcu_read_lock() because you have a known reference
> to 'idev' in these paths, but you can't get rid of the address list locking
> altogether.
(Apologize for the delay...)
The upper callers of mld_newpack() already take
read_lock_bh(&idev->lock):
mld_newpack() ...-> add_grec() -|-> mld_send_cr() LOCKED
|-> mld_send_report() LOCKED
therefore it is safe to travel idev->addr_list locklessly here.
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