From: Stephen Hemminger <shemminger@vyatta.com>
To: Eric Dumazet <erdnetdev@gmail.com>
Cc: Yan Burman <yanb@mellanox.com>, netdev@vger.kernel.org
Subject: Re: Lockdep warning in vxlan
Date: Thu, 20 Dec 2012 10:22:12 -0800 [thread overview]
Message-ID: <20121220102212.03dd1a3d@nehalam.linuxnetplumber.net> (raw)
In-Reply-To: <1356027360.21834.2973.camel@edumazet-glaptop>
On Thu, 20 Dec 2012 10:16:00 -0800
Eric Dumazet <erdnetdev@gmail.com> wrote:
> On Thu, 2012-12-20 at 08:34 -0800, Stephen Hemminger wrote:
> > On Thu, 20 Dec 2012 16:00:32 +0200
> > Yan Burman <yanb@mellanox.com> wrote:
> >
> > > Hi.
> > >
> > > When working with vxlan from current net-next, I got a lockdep warning
> > > (below).
> > > It seems to happen when I have host B pinging host A and while the pings
> > > continue,
> > > I do "ip link del" on the vxlan interface on host A. The lockdep warning
> > > is on host A.
> > > Tell me if you need some more info.
> > >
> >
> > Looks like the case of nested ARP requests, the initial request is coming
> > from neigh_timer (ARP retransmit), but inside neigh_probe the lock
> > is dropped?
>
> Bug is from arp_solicit(), releasing the lock after arp_send()
>
> Its used to protect neigh->ha
>
> We could instead copy neigh->ha, without taking n->lock but ha_lock
> seqlock, using neigh_ha_snapshot() helper
>
> Yan, could you test the following patch ?
>
> Thanks
> diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
> index ce6fbdf..1169ed4 100644
> --- a/net/ipv4/arp.c
> +++ b/net/ipv4/arp.c
> @@ -321,7 +321,7 @@ static void arp_error_report(struct neighbour *neigh, struct sk_buff *skb)
> static void arp_solicit(struct neighbour *neigh, struct sk_buff *skb)
> {
> __be32 saddr = 0;
> - u8 *dst_ha = NULL;
> + u8 dst_ha[MAX_ADDR_LEN];
> struct net_device *dev = neigh->dev;
> __be32 target = *(__be32 *)neigh->primary_key;
> int probes = atomic_read(&neigh->probes);
> @@ -363,9 +363,9 @@ static void arp_solicit(struct neighbour *neigh, struct sk_buff *skb)
> if (probes < 0) {
> if (!(neigh->nud_state & NUD_VALID))
> pr_debug("trying to ucast probe in NUD_INVALID\n");
> - dst_ha = neigh->ha;
> - read_lock_bh(&neigh->lock);
> + neigh_ha_snapshot(dst_ha, neigh, dev);
> } else {
> + memset(dst_ha, 0, dev->addr_len);
> probes -= neigh->parms->app_probes;
> if (probes < 0) {
> #ifdef CONFIG_ARPD
> @@ -377,8 +377,6 @@ static void arp_solicit(struct neighbour *neigh, struct sk_buff *skb)
>
> arp_send(ARPOP_REQUEST, ETH_P_ARP, target, dev, saddr,
> dst_ha, dev->dev_addr, NULL);
> - if (dst_ha)
> - read_unlock_bh(&neigh->lock);
> }
>
> static int arp_ignore(struct in_device *in_dev, __be32 sip, __be32 tip)
I like this. Getting rid of yet another read lock
next prev parent reply other threads:[~2012-12-20 18:23 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-20 14:00 Lockdep warning in vxlan Yan Burman
2012-12-20 16:34 ` Stephen Hemminger
2012-12-20 18:16 ` Eric Dumazet
2012-12-20 18:22 ` Stephen Hemminger [this message]
2012-12-23 9:41 ` Yan Burman
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