netdev - Re: [PATCH net 4/4] tcp: various missing rcu_read_lock around __sk_dst

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Date:	Fri, 01 Apr 2016 05:31:25 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	sasha.levin@...cle.com, daniel@...earbox.net,
	alexei.starovoitov@...il.com, mkubecek@...e.cz
Subject: Re: [PATCH net 4/4] tcp: various missing rcu_read_lock around
 __sk_dst_get



On Fri, Apr 1, 2016, at 05:13, Eric Dumazet wrote:
> On Fri, 2016-04-01 at 04:01 +0200, Hannes Frederic Sowa wrote:
> 
> > I thought so first, as well. But given the double check for the 
> > spin_lock and the "mutex" we end up with the same result for the 
> > lockdep_sock_is_held check.
> > 
> > Do you see other consequences?
> 
> Well, we release the spinlock in __release_sock()
> 
> So another thread could come and acquire the socket, then call
> mutex_acquire() while the first thread did not call yet mutex_release()
> 
> So maybe lockdep will complain (but I do not know lockdep enough to
> tell)
> 
> So maybe the following would be better :
> 
> (Absolutely untested, really I need to take a break)

I quickly tested the patch and my scripts didn't show any splats so far.
This patch seems more consistent albeit I don't think it is relevant for
lockdep_sock_is_held as we only flip owned while holding slock. But this
definitely needs more review.

Thanks a lot!