netdev - Re: linux-next: zillions of lockdep whinges in include/net/sock.h:1408

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Date:	Sun, 24 Apr 2016 14:28:08 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Valdis.Kletnieks@...edu
Cc:	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: linux-next: zillions of lockdep whinges in
 include/net/sock.h:1408

On Sun, 2016-04-24 at 14:25 -0700, Eric Dumazet wrote:
> On Sun, 2016-04-24 at 17:13 -0400, Valdis.Kletnieks@...edu wrote:
> > On Sun, 24 Apr 2016 14:00:17 -0700, Eric Dumazet said:
> > > On Sun, 2016-04-24 at 15:56 -0400, Valdis.Kletnieks@...edu wrote:
> > > > On Sun, 24 Apr 2016 12:46:42 -0700, Eric Dumazet said:
> > > >
> > > > > >>> +	return !debug_locks ||
> > > > > >>> +	       lockdep_is_held(&sk->sk_lock) ||
> > > >
> > > > > Issue here is that once lockdep detected a problem (not necessarily in
> > > > > net/ tree btw), your helper always 'detect' a problem, since lockdep
> > > > > automatically disables itself.
> > > >
> > > > "D'Oh!" -- H. Simpson
> > > >
> > > > I thought this patch looked suspect, but couldn't put my finger on it. The
> > > > reason why I got like 41,000 of them is because I built a kernel that has
> > > > lockdep enabled, but I have an out-of-tree module that doesn't init something,
> > > > so I get this:
> > > >
> > > > [   48.898156] INFO: trying to register non-static key.
> > > > [   48.898157] the code is fine but needs lockdep annotation.
> > > > [   48.898157] turning off the locking correctness validator.
> > > >
> > > > After which point, even with this patch, every time through it's still going to
> > > > explode.
> > >
> > > Which patch are you talking about ?
> > 
> > The one that adds the !debug_locks check - once my out-of-kernel module
> > hits something that turns off lockdep, it's *still* going to complain on
> > pretty much all the same packets it complained about earlier.  I thought
> > it looked suspicious, but you clarified why...
> 
> It does not make sense to me. If lockdep is disabled, then debug_locks
> is 0.
> 
> So no complain should happen from networking.
> 
> I was about to send following patch, please check it solves the issue. ?
> 
> (It certainly did for me, once I forced a lockdep splat loading a buggy
> module)
> 
> Thanks
> 
> From: Eric Dumazet <edumazet@...gle.com>
> 
> Valdis reported tons of stack dumps caused by WARN_ON() in sock_owned_by_user()
> 
> This test needs to be relaxed if/when lockdep disables itself.
> 
> Note that other lockdep_sock_is_held() callers are all from
> rcu_dereference_protected() sections which already are disabled
> if/when lockdep has been disabled.
> 
> Fixes: fafc4e1ea1a4 ("sock: tigthen lockdep checks for sock_owned_by_user")
> Reported-by: Valdis Kletnieks <Valdis.Kletnieks@...edu>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> ---
>  include/net/sock.h |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/net/sock.h b/include/net/sock.h
> index 52448baf19d7..f492d01512ed 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -1409,7 +1409,7 @@ static inline void unlock_sock_fast(struct sock *sk, bool slow)
>  static inline bool sock_owned_by_user(const struct sock *sk)
>  {
>  #ifdef CONFIG_LOCKDEP
> -	WARN_ON(!lockdep_sock_is_held(sk));
> +	WARN_ON_ONCE(!lockdep_sock_is_held(sk) && !debug_locks);


Silly me, I tested the opposite test of course :

WARN_ON_ONCE(!lockdep_sock_is_held(sk) && debug_locks);

>  #endif
>  	return sk->sk_lock.owned;
>  }
>