linux-kernel - Re: [PATCH RESEND] spin_lock_*(): Always evaluate second argument

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Message-ID: <alpine.DEB.2.02.1407221612330.10592@chino.kir.corp.google.com>
Date:	Tue, 22 Jul 2014 16:16:15 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Bart Van Assche <bvanassche@....org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"David S. Miller" <davem@...emloft.net>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RESEND] spin_lock_*(): Always evaluate second argument

On Tue, 22 Jul 2014, Andrew Morton wrote:

> > Evaluating a macro argument only if certain configuration options
> > have been selected is confusing and error-prone. Hence always
> > evaluate the second argument of spin_lock_nested() and
> > spin_lock_nest_lock().
> > 
> > An intentional side effect of this patch is that it avoids that
> > the following warning is reported for netif_addr_lock_nested()
> > when building with CONFIG_DEBUG_LOCK_ALLOC=n and with W=1:
> > 
> > ...
> >
> > --- a/include/linux/spinlock.h
> > +++ b/include/linux/spinlock.h
> > @@ -197,8 +197,10 @@ static inline void do_raw_spin_unlock(raw_spinlock_t *lock) __releases(lock)
> >  		 _raw_spin_lock_nest_lock(lock, &(nest_lock)->dep_map);	\
> >  	 } while (0)
> >  #else
> > -# define raw_spin_lock_nested(lock, subclass)		_raw_spin_lock(lock)
> > -# define raw_spin_lock_nest_lock(lock, nest_lock)	_raw_spin_lock(lock)
> > +# define raw_spin_lock_nested(lock, subclass)		\
> > +	((void)(subclass), _raw_spin_lock(lock))
> > +# define raw_spin_lock_nest_lock(lock, nest_lock)	\
> > +	((void)(nest_lock), _raw_spin_lock(lock))
> >  #endif
> >  
> 
> Did you try converting these to static inline functions?  That should
> squish the warning and makes the code nicer instead of nastier...
> 

Not sure how that would be done since _raw_spin_lock isn't declared in 
this scope.

Taking a second look, however, I think the patch doesn't need to modify 
raw_spin_lock_nest_lock() for the problem being reported and evaluating 
the parameter of type struct lockdep_map * probably is meaningless.

Bart, is it possible to just get away with the raw_spin_lock_nested() 
change?
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