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

From: Bart Van Assche
Date: Wed Aug 06 2014 - 13:27:04 EST


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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