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From: David Miller <davem@davemloft.net>
To: eric.dumazet@gmail.com
Cc: therbert@google.com, alexander.h.duyck@intel.com, netdev@vger.kernel.org
Subject: Re: [PATCH v2 net-next] tcp: remove dst refcount false sharing for prequeue mode
Date: Mon, 08 Sep 2014 14:21:43 -0700 (PDT)	[thread overview]
Message-ID: <20140908.142143.807176983873922125.davem@davemloft.net> (raw)
In-Reply-To: <1410188767.11872.110.camel@edumazet-glaptop2.roam.corp.google.com>

From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Mon, 08 Sep 2014 08:06:07 -0700

> @@ -1559,7 +1559,17 @@ bool tcp_prequeue(struct sock *sk, struct sk_buff *skb)
>  	    skb_queue_len(&tp->ucopy.prequeue) == 0)
>  		return false;
>  
> -	skb_dst_force(skb);
> +	/* Before escaping RCU protected region, we need to take care of skb
> +	 * dst. Prequeue is only enabled for established sockets.
> +	 * For such sockets, we might need the skb dst only to set sk->sk_rx_dst
> +	 * Instead of doing full sk_rx_dst validity here, let's perform
> +	 * an optimistic check.
> +	 */
> +	if (likely(sk->sk_rx_dst))
> +		skb_dst_drop(skb);
> +	else
> +		skb_dst_force(skb);
> +

This might not be a strong enough test.

We have to also make all of the checks that would cause the input
path to invalidate sk->sk_rx_dst too.

Otherwise, if it does, we'll crash when we try to do a dst_hold()
on skb_dst(skb) in sk->sk_rx_dst_set().

  reply	other threads:[~2014-09-08 21:21 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-08-14 18:19 Performance regression on kernels 3.10 and newer Alexander Duyck
2014-08-14 18:46 ` Eric Dumazet
2014-08-14 19:50   ` Eric Dumazet
2014-08-14 19:59   ` Rick Jones
2014-08-14 20:31     ` Alexander Duyck
2014-08-14 20:51       ` Eric Dumazet
2014-08-14 20:46     ` Eric Dumazet
2014-08-14 23:16   ` Alexander Duyck
2014-08-14 23:20     ` David Miller
2014-08-14 23:25       ` Tom Herbert
2014-08-21 23:24         ` David Miller
2014-09-06 14:45           ` Eric Dumazet
2014-09-06 15:27             ` Eric Dumazet
2014-09-06 15:46               ` Eric Dumazet
2014-09-06 16:38                 ` Eric Dumazet
2014-09-06 18:21                   ` Eric Dumazet
2014-09-07 19:05                     ` [PATCH net] ipv6: refresh rt6i_genid in ip6_pol_route() Eric Dumazet
2014-09-07 22:54                       ` David Miller
2014-09-08  4:18                         ` Eric Dumazet
2014-09-08  4:27                           ` David Miller
2014-09-08  4:43                             ` Eric Dumazet
2014-09-08  4:59                               ` David Miller
2014-09-08  5:07                                 ` Eric Dumazet
2014-09-08  8:11                                   ` Nicolas Dichtel
2014-09-08 10:28                                     ` Eric Dumazet
2014-09-08 12:16                                       ` Nicolas Dichtel
2014-09-08 18:48                                   ` Vlad Yasevich
2014-09-09 12:58                                   ` Hannes Frederic Sowa
2014-09-10  9:31                                     ` [PATCH net-next] ipv6: implement rt_genid_bump_ipv6 with fn_sernum and remove rt6i_genid Hannes Frederic Sowa
2014-09-10 13:26                                       ` Vlad Yasevich
2014-09-10 13:42                                         ` Hannes Frederic Sowa
2014-09-10 20:09                                       ` David Miller
2014-09-11  8:30                                         ` Hannes Frederic Sowa
2014-09-11 12:22                                           ` Vlad Yasevich
2014-09-11 12:40                                             ` Hannes Frederic Sowa
2014-09-11 12:05                                         ` Hannes Frederic Sowa
2014-09-11 14:19                                           ` Vlad Yasevich
2014-09-11 14:32                                             ` Hannes Frederic Sowa
2014-09-11 14:44                                               ` Vlad Yasevich
2014-09-11 14:47                                                 ` Hannes Frederic Sowa
2014-09-08 15:06               ` [PATCH v2 net-next] tcp: remove dst refcount false sharing for prequeue mode Eric Dumazet
2014-09-08 21:21                 ` David Miller [this message]
2014-09-08 21:30                   ` Eric Dumazet
2014-09-08 22:41                     ` David Miller
2014-09-09 23:56                     ` David Miller
2014-08-15 17:15       ` Performance regression on kernels 3.10 and newer Alexander Duyck
2014-08-15 17:59         ` Eric Dumazet
2014-08-15 18:49         ` Tom Herbert
2014-08-15 19:10           ` Alexander Duyck
2014-08-15 22:16             ` Tom Herbert
2014-08-15 23:23               ` Alexander Duyck
2014-08-18  9:03                 ` David Laight
2014-08-18 15:22                   ` Alexander Duyck
2014-08-18 15:29                     ` Rick Jones
2014-08-21 23:51         ` David Miller
2014-08-14 23:48     ` Eric Dumazet
2014-08-15  0:33       ` Rick Jones

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