linux-kernel - Re: [PATCH] inet: further fixes of possible seqlock deadlocks

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Message-ID: <1385672502.5352.38.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 28 Nov 2013 13:01:42 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	jongman.heo@...sung.com, David Miller <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] inet: further fixes of possible seqlock deadlocks

On Thu, 2013-11-28 at 20:22 +0100, Hannes Frederic Sowa wrote:
> This fixes more incorrect uses of *_STATS_BH in process context.
> 
> Cc: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Hannes Frederic Sowa <hannes@...essinduktion.org>
> ---
>  net/ipv4/udp.c        | 8 ++++----
>  net/ipv6/ip6_output.c | 8 ++++----
>  net/ipv6/ping.c       | 4 ++--
>  3 files changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> index 44e3884..f5cc018 100644
> --- a/net/ipv4/udp.c
> +++ b/net/ipv4/udp.c
> @@ -1160,10 +1160,10 @@ static unsigned int first_packet_length(struct sock *sk)
>  	spin_lock_bh(&rcvq->lock);

Here we block BH, because of spin_lock_bh()

>  	while ((skb = skb_peek(rcvq)) != NULL &&
>  		udp_lib_checksum_complete(skb)) {
> -		UDP_INC_STATS_BH(sock_net(sk), UDP_MIB_CSUMERRORS,
> -				 IS_UDPLITE(sk));
> -		UDP_INC_STATS_BH(sock_net(sk), UDP_MIB_INERRORS,
> -				 IS_UDPLITE(sk));

So this is the right thing, this change is not needed.

> +		UDP_INC_STATS_USER(sock_net(sk), UDP_MIB_CSUMERRORS,
> +				   IS_UDPLITE(sk));
> +		UDP_INC_STATS_USER(sock_net(sk), UDP_MIB_INERRORS,
> +				   IS_UDPLITE(sk));
>  		atomic_inc(&sk->sk_drops);
>  		__skb_unlink(skb, rcvq);
>  		__skb_queue_tail(&list_kill, skb);
> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> index 59df872..e05cf0a 100644
> --- a/net/ipv6/ip6_output.c
> +++ b/j
> @@ -116,8 +116,8 @@ static int ip6_finish_output2(struct sk_buff *skb)
>  	}
>  	rcu_read_unlock_bh();
>  
> -	IP6_INC_STATS_BH(dev_net(dst->dev),
> -			 ip6_dst_idev(dst), IPSTATS_MIB_OUTNOROUTES);
> +	IP6_INC_STATS(dev_net(dst->dev),
> +		      ip6_dst_idev(dst), IPSTATS_MIB_OUTNOROUTES);

This is ipv6, not inet changes ;)

>  	kfree_skb(skb);
>  	return -EINVAL;
>  }
> @@ -1524,8 +1524,8 @@ int ip6_push_pending_frames(struct sock *sk)
>  	if (proto == IPPROTO_ICMPV6) {
>  		struct inet6_dev *idev = ip6_dst_idev(skb_dst(skb));
>  
> -		ICMP6MSGOUT_INC_STATS_BH(net, idev, icmp6_hdr(skb)->icmp6_type);
> -		ICMP6_INC_STATS_BH(net, idev, ICMP6_MIB_OUTMSGS);
> +		ICMP6MSGOUT_INC_STATS(net, idev, icmp6_hdr(skb)->icmp6_type);
> +		ICMP6_INC_STATS(net, idev, ICMP6_MIB_OUTMSGS);

I am not sure we use a seqlock for ICMP stats.

seqlocks were used for 64bit IP stats



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