netdev - Re: [PATCH net-next v10 05/11] ipv6: do not call ndisc_send

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Date:	Wed, 28 Aug 2013 17:34:50 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Cong Wang <amwang@...hat.com>
Cc:	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next v10 05/11] ipv6: do not call ndisc_send_rs() with write lock

On Wed, Aug 28, 2013 at 01:22:53PM +0800, Cong Wang wrote:
> From: Cong Wang <amwang@...hat.com>
> 
> Because vxlan module will call ip6_dst_lookup() in TX path,
> which will hold write lock. So we have to release this write lock
> before calling ndisc_send_rs(), otherwise could deadlock.
> 
> Signed-off-by: Cong Wang <amwang@...hat.com>

Change seems fine:

Reviewed-by: Hannes Frederic Sowa <hannes@...essinduktion.org>

> ---
>  net/ipv6/addrconf.c |   10 +++++++---
>  1 files changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index 8e68466..1bb0861 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -3088,6 +3088,7 @@ static int addrconf_ifdown(struct net_device *dev, int how)
>  static void addrconf_rs_timer(unsigned long data)
>  {
>  	struct inet6_dev *idev = (struct inet6_dev *)data;
> +	struct net_device *dev = idev->dev;
>  	struct in6_addr lladdr;
>  
>  	write_lock(&idev->lock);
> @@ -3102,12 +3103,14 @@ static void addrconf_rs_timer(unsigned long data)
>  		goto out;
>  
>  	if (idev->rs_probes++ < idev->cnf.rtr_solicits) {
> -		if (!__ipv6_get_lladdr(idev, &lladdr, IFA_F_TENTATIVE))
> -			ndisc_send_rs(idev->dev, &lladdr,
> +		write_unlock(&idev->lock);
> +		if (!ipv6_get_lladdr(dev, &lladdr, IFA_F_TENTATIVE))
> +			ndisc_send_rs(dev, &lladdr,
>  				      &in6addr_linklocal_allrouters);
>  		else
> -			goto out;
> +			goto put;
>  
> +		write_lock(&idev->lock);
>  		/* The wait after the last probe can be shorter */
>  		addrconf_mod_rs_timer(idev, (idev->rs_probes ==
>  					     idev->cnf.rtr_solicits) ?
> @@ -3123,6 +3126,7 @@ static void addrconf_rs_timer(unsigned long data)
>  
>  out:
>  	write_unlock(&idev->lock);
> +put:
>  	in6_dev_put(idev);
>  }

Maybe it would be cleaner to just update a boolean in the inner block
and call ndisc_send_rs after the write_unlock.

Greetings,

  Hannes

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