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

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Message-ID: <53E260D9.6030803@acm.org>
Date:	Wed, 06 Aug 2014 19:07:37 +0200
From:	Bart Van Assche <bvanassche@....org>
To:	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	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 07/23/14 01:16, David Rientjes wrote:
> 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?

Probably ... I will post an updated version of this patch.

Bart.
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