Re: [PATCH] lockdep: constify usage of struct lock_class_key where possible

[Heiner Kallweit <hkallweit1@gmail.com>]

On 04.05.2026 09:28, Peter Zijlstra wrote:
> On Tue, Apr 28, 2026 at 11:05:25PM +0200, Heiner Kallweit wrote:
>> Constify usage of struct lock_class_key where possible. This requires
>> to constify also usage of struct lockdep_subclass_key in two places.
>>
>> Especially relevant is constification of lockdep_map.key, as it makes
>> clear that the key isn't changed during lifetime of struct lockdep_map.
>>
>> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
>> ---
>>  include/linux/lockdep.h       | 18 ++++++++++--------
>>  include/linux/lockdep_types.h |  2 +-
>>  kernel/locking/lockdep.c      | 12 ++++++------
>>  3 files changed, 17 insertions(+), 15 deletions(-)
>>
>> diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
>> index 621566345..3fa2b62f2 100644
>> --- a/include/linux/lockdep.h
>> +++ b/include/linux/lockdep.h
>> @@ -125,25 +125,27 @@ extern void lockdep_unregister_key(struct lock_class_key *key);
>>   * to lockdep:
>>   */
>>  
>> -extern void lockdep_init_map_type(struct lockdep_map *lock, const char *name,
>> -	struct lock_class_key *key, int subclass, u8 inner, u8 outer, u8 lock_type);
>> +void lockdep_init_map_type(struct lockdep_map *lock, const char *name,
>> +			   const struct lock_class_key *key, int subclass,
>> +			   u8 inner, u8 outer, u8 lock_type);
> 
>> @@ -252,9 +254,9 @@ static inline int lock_is_held(const struct lockdep_map *lock)
>>  #define lockdep_is_held(lock)		lock_is_held(&(lock)->dep_map)
>>  #define lockdep_is_held_type(lock, r)	lock_is_held_type(&(lock)->dep_map, (r))
>>  
>> -extern void lock_set_class(struct lockdep_map *lock, const char *name,
>> -			   struct lock_class_key *key, unsigned int subclass,
>> -			   unsigned long ip);
>> +void lock_set_class(struct lockdep_map *lock, const char *name,
>> +		    const struct lock_class_key *key, unsigned int subclass,
>> +		    unsigned long ip);
>>  
> 
> It is also silently removing extern, why?

When touching this function prototype anyway, make it compliant with coding standard.
See https://www.kernel.org/doc/html/v7.0/process/coding-style.html, section 6.1.
"Do not use the extern keyword with function declarations as this makes lines longer
and isn’t strictly necessary."