netdev - Re: [PATCH] net-tcp: fix panic in tcp_fastopen_cache

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Date:	Thu, 14 Nov 2013 11:38:42 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	Dave Jones <davej@...hat.com>, David Miller <davem@...emloft.net>,
	netdev@...r.kernel.org, Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH] net-tcp: fix panic in tcp_fastopen_cache_set()

On Thu, 2013-11-14 at 11:36 -0800, Eric Dumazet wrote:
> On Thu, 2013-11-14 at 20:13 +0100, Johannes Berg wrote:
> > On Wed, 2013-11-13 at 15:00 -0800, Eric Dumazet wrote:
> > 
> > > --- a/net/ipv4/tcp_metrics.c
> > > +++ b/net/ipv4/tcp_metrics.c
> > > @@ -663,10 +663,13 @@ void tcp_fastopen_cache_get(struct sock *sk, u16 *mss,
> > >  void tcp_fastopen_cache_set(struct sock *sk, u16 mss,
> > >  			    struct tcp_fastopen_cookie *cookie, bool syn_lost)
> > >  {
> > > +	struct dst_entry *dst = __sk_dst_get(sk);
> > >  	struct tcp_metrics_block *tm;
> > >  
> > > +	if (!dst)
> > > +		return;
> > >  	rcu_read_lock();
> > > -	tm = tcp_get_metrics(sk, __sk_dst_get(sk), true);
> > 
> > Doesn't that __sk_dst_get() have to go inside the rcu_read_lock()?
> > 
> > Then again, I guess we hold the socket. Still looks a bit weird to be
> > moving it out.
> 
> Yep, in fact this rcu_read_lock() is not needed. I'll send a v2.

I take it back.

the rcu_read_lock() protects the tcp_get_metrics(), not the
__sk_dst_get(sk)

So the patch is correct, unless you disagree of course ;)


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