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

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

[Heiner Kallweit]

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);
 
 static inline void
 lockdep_init_map_waits(struct lockdep_map *lock, const char *name,
-		       struct lock_class_key *key, int subclass, u8 inner, u8 outer)
+		       const struct lock_class_key *key, int subclass,
+		       u8 inner, u8 outer)
 {
 	lockdep_init_map_type(lock, name, key, subclass, inner, outer, LD_LOCK_NORMAL);
 }
 
 static inline void
 lockdep_init_map_wait(struct lockdep_map *lock, const char *name,
-		      struct lock_class_key *key, int subclass, u8 inner)
+		      const struct lock_class_key *key, int subclass, u8 inner)
 {
 	lockdep_init_map_waits(lock, name, key, subclass, inner, LD_WAIT_INV);
 }
 
 static inline void lockdep_init_map(struct lockdep_map *lock, const char *name,
-			     struct lock_class_key *key, int subclass)
+				    const struct lock_class_key *key, int subclass)
 {
 	lockdep_init_map_wait(lock, name, key, subclass, LD_WAIT_INV);
 }
@@ -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);
 
 #define lock_set_novalidate_class(l, n, i) \
 	lock_set_class(l, n, &__lockdep_no_validate__, 0, i)
diff --git a/include/linux/lockdep_types.h b/include/linux/lockdep_types.h
index eae115a26..0d3df9019 100644
--- a/include/linux/lockdep_types.h
+++ b/include/linux/lockdep_types.h
@@ -184,7 +184,7 @@ void clear_lock_stats(struct lock_class *class);
  * This is embedded into specific lock instances:
  */
 struct lockdep_map {
-	struct lock_class_key		*key;
+	const struct lock_class_key		*key;
 	struct lock_class		*class_cache[NR_LOCKDEP_CACHING_CLASSES];
 	const char			*name;
 	u8				wait_type_outer; /* can be taken in this context */
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index f13883162..fe1415260 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -888,7 +888,7 @@ static int count_matching_names(struct lock_class *new_class)
 static noinstr struct lock_class *
 look_up_lock_class(const struct lockdep_map *lock, unsigned int subclass)
 {
-	struct lockdep_subclass_key *key;
+	const struct lockdep_subclass_key *key;
 	struct hlist_head *hash_head;
 	struct lock_class *class;
 
@@ -1286,7 +1286,7 @@ static bool is_dynamic_key(const struct lock_class_key *key)
 static struct lock_class *
 register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
 {
-	struct lockdep_subclass_key *key;
+	const struct lockdep_subclass_key *key;
 	struct hlist_head *hash_head;
 	struct lock_class *class;
 	int idx;
@@ -4937,8 +4937,8 @@ static inline int check_wait_context(struct task_struct *curr,
  * Initialize a lock instance's lock-class mapping info:
  */
 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)
+			   const struct lock_class_key *key, int subclass,
+			   u8 inner, u8 outer, u8 lock_type)
 {
 	int i;
 
@@ -5408,7 +5408,7 @@ static int reacquire_held_locks(struct task_struct *curr, unsigned int depth,
 
 static int
 __lock_set_class(struct lockdep_map *lock, const char *name,
-		 struct lock_class_key *key, unsigned int subclass,
+		 const struct lock_class_key *key, unsigned int subclass,
 		 unsigned long ip)
 {
 	struct task_struct *curr = current;
@@ -5733,7 +5733,7 @@ static noinstr void check_flags(unsigned long flags)
 }
 
 void lock_set_class(struct lockdep_map *lock, const char *name,
-		    struct lock_class_key *key, unsigned int subclass,
+		    const struct lock_class_key *key, unsigned int subclass,
 		    unsigned long ip)
 {
 	unsigned long flags;
-- 
2.54.0

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

[Waiman Long]

On 4/28/26 5:05 PM, 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.

Other than making clear that the lock_class_key isn't being modified, is 
there other benefit of making this change like helping compiler to 
generate better code?

Cheers,
Longman

>
> 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);
>   
>   static inline void
>   lockdep_init_map_waits(struct lockdep_map *lock, const char *name,
> -		       struct lock_class_key *key, int subclass, u8 inner, u8 outer)
> +		       const struct lock_class_key *key, int subclass,
> +		       u8 inner, u8 outer)
>   {
>   	lockdep_init_map_type(lock, name, key, subclass, inner, outer, LD_LOCK_NORMAL);
>   }
>   
>   static inline void
>   lockdep_init_map_wait(struct lockdep_map *lock, const char *name,
> -		      struct lock_class_key *key, int subclass, u8 inner)
> +		      const struct lock_class_key *key, int subclass, u8 inner)
>   {
>   	lockdep_init_map_waits(lock, name, key, subclass, inner, LD_WAIT_INV);
>   }
>   
>   static inline void lockdep_init_map(struct lockdep_map *lock, const char *name,
> -			     struct lock_class_key *key, int subclass)
> +				    const struct lock_class_key *key, int subclass)
>   {
>   	lockdep_init_map_wait(lock, name, key, subclass, LD_WAIT_INV);
>   }
> @@ -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);
>   
>   #define lock_set_novalidate_class(l, n, i) \
>   	lock_set_class(l, n, &__lockdep_no_validate__, 0, i)
> diff --git a/include/linux/lockdep_types.h b/include/linux/lockdep_types.h
> index eae115a26..0d3df9019 100644
> --- a/include/linux/lockdep_types.h
> +++ b/include/linux/lockdep_types.h
> @@ -184,7 +184,7 @@ void clear_lock_stats(struct lock_class *class);
>    * This is embedded into specific lock instances:
>    */
>   struct lockdep_map {
> -	struct lock_class_key		*key;
> +	const struct lock_class_key		*key;
>   	struct lock_class		*class_cache[NR_LOCKDEP_CACHING_CLASSES];
>   	const char			*name;
>   	u8				wait_type_outer; /* can be taken in this context */
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index f13883162..fe1415260 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -888,7 +888,7 @@ static int count_matching_names(struct lock_class *new_class)
>   static noinstr struct lock_class *
>   look_up_lock_class(const struct lockdep_map *lock, unsigned int subclass)
>   {
> -	struct lockdep_subclass_key *key;
> +	const struct lockdep_subclass_key *key;
>   	struct hlist_head *hash_head;
>   	struct lock_class *class;
>   
> @@ -1286,7 +1286,7 @@ static bool is_dynamic_key(const struct lock_class_key *key)
>   static struct lock_class *
>   register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
>   {
> -	struct lockdep_subclass_key *key;
> +	const struct lockdep_subclass_key *key;
>   	struct hlist_head *hash_head;
>   	struct lock_class *class;
>   	int idx;
> @@ -4937,8 +4937,8 @@ static inline int check_wait_context(struct task_struct *curr,
>    * Initialize a lock instance's lock-class mapping info:
>    */
>   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)
> +			   const struct lock_class_key *key, int subclass,
> +			   u8 inner, u8 outer, u8 lock_type)
>   {
>   	int i;
>   
> @@ -5408,7 +5408,7 @@ static int reacquire_held_locks(struct task_struct *curr, unsigned int depth,
>   
>   static int
>   __lock_set_class(struct lockdep_map *lock, const char *name,
> -		 struct lock_class_key *key, unsigned int subclass,
> +		 const struct lock_class_key *key, unsigned int subclass,
>   		 unsigned long ip)
>   {
>   	struct task_struct *curr = current;
> @@ -5733,7 +5733,7 @@ static noinstr void check_flags(unsigned long flags)
>   }
>   
>   void lock_set_class(struct lockdep_map *lock, const char *name,
> -		    struct lock_class_key *key, unsigned int subclass,
> +		    const struct lock_class_key *key, unsigned int subclass,
>   		    unsigned long ip)
>   {
>   	unsigned long flags;

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

[Heiner Kallweit]

On 29.04.2026 19:04, Waiman Long wrote:
> On 4/28/26 5:05 PM, 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.
> 
> Other than making clear that the lock_class_key isn't being modified, is there other benefit of making this change like helping compiler to generate better code?
> 
Doing an objdump -o kernel/locking/lockdep.o I see no difference in section
sizes. Hence at least with gcc it doesn't seem to affect code generation.
I didn't check whether it affects callers of e.g. lockdep_init_map_wait().

> Cheers,
> Longman
> 
>>
>> 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);
>>     static inline void
>>   lockdep_init_map_waits(struct lockdep_map *lock, const char *name,
>> -               struct lock_class_key *key, int subclass, u8 inner, u8 outer)
>> +               const struct lock_class_key *key, int subclass,
>> +               u8 inner, u8 outer)
>>   {
>>       lockdep_init_map_type(lock, name, key, subclass, inner, outer, LD_LOCK_NORMAL);
>>   }
>>     static inline void
>>   lockdep_init_map_wait(struct lockdep_map *lock, const char *name,
>> -              struct lock_class_key *key, int subclass, u8 inner)
>> +              const struct lock_class_key *key, int subclass, u8 inner)
>>   {
>>       lockdep_init_map_waits(lock, name, key, subclass, inner, LD_WAIT_INV);
>>   }
>>     static inline void lockdep_init_map(struct lockdep_map *lock, const char *name,
>> -                 struct lock_class_key *key, int subclass)
>> +                    const struct lock_class_key *key, int subclass)
>>   {
>>       lockdep_init_map_wait(lock, name, key, subclass, LD_WAIT_INV);
>>   }
>> @@ -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);
>>     #define lock_set_novalidate_class(l, n, i) \
>>       lock_set_class(l, n, &__lockdep_no_validate__, 0, i)
>> diff --git a/include/linux/lockdep_types.h b/include/linux/lockdep_types.h
>> index eae115a26..0d3df9019 100644
>> --- a/include/linux/lockdep_types.h
>> +++ b/include/linux/lockdep_types.h
>> @@ -184,7 +184,7 @@ void clear_lock_stats(struct lock_class *class);
>>    * This is embedded into specific lock instances:
>>    */
>>   struct lockdep_map {
>> -    struct lock_class_key        *key;
>> +    const struct lock_class_key        *key;
>>       struct lock_class        *class_cache[NR_LOCKDEP_CACHING_CLASSES];
>>       const char            *name;
>>       u8                wait_type_outer; /* can be taken in this context */
>> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
>> index f13883162..fe1415260 100644
>> --- a/kernel/locking/lockdep.c
>> +++ b/kernel/locking/lockdep.c
>> @@ -888,7 +888,7 @@ static int count_matching_names(struct lock_class *new_class)
>>   static noinstr struct lock_class *
>>   look_up_lock_class(const struct lockdep_map *lock, unsigned int subclass)
>>   {
>> -    struct lockdep_subclass_key *key;
>> +    const struct lockdep_subclass_key *key;
>>       struct hlist_head *hash_head;
>>       struct lock_class *class;
>>   @@ -1286,7 +1286,7 @@ static bool is_dynamic_key(const struct lock_class_key *key)
>>   static struct lock_class *
>>   register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
>>   {
>> -    struct lockdep_subclass_key *key;
>> +    const struct lockdep_subclass_key *key;
>>       struct hlist_head *hash_head;
>>       struct lock_class *class;
>>       int idx;
>> @@ -4937,8 +4937,8 @@ static inline int check_wait_context(struct task_struct *curr,
>>    * Initialize a lock instance's lock-class mapping info:
>>    */
>>   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)
>> +               const struct lock_class_key *key, int subclass,
>> +               u8 inner, u8 outer, u8 lock_type)
>>   {
>>       int i;
>>   @@ -5408,7 +5408,7 @@ static int reacquire_held_locks(struct task_struct *curr, unsigned int depth,
>>     static int
>>   __lock_set_class(struct lockdep_map *lock, const char *name,
>> -         struct lock_class_key *key, unsigned int subclass,
>> +         const struct lock_class_key *key, unsigned int subclass,
>>            unsigned long ip)
>>   {
>>       struct task_struct *curr = current;
>> @@ -5733,7 +5733,7 @@ static noinstr void check_flags(unsigned long flags)
>>   }
>>     void lock_set_class(struct lockdep_map *lock, const char *name,
>> -            struct lock_class_key *key, unsigned int subclass,
>> +            const struct lock_class_key *key, unsigned int subclass,
>>               unsigned long ip)
>>   {
>>       unsigned long flags;
> 

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

[Waiman Long]

On 4/29/26 3:40 PM, Heiner Kallweit wrote:
> On 29.04.2026 19:04, Waiman Long wrote:
>> On 4/28/26 5:05 PM, 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.
>> Other than making clear that the lock_class_key isn't being modified, is there other benefit of making this change like helping compiler to generate better code?
>>
> Doing an objdump -o kernel/locking/lockdep.o I see no difference in section
> sizes. Hence at least with gcc it doesn't seem to affect code generation.
> I didn't check whether it affects callers of e.g. lockdep_init_map_wait().

I asked because just stating the nature of the lock_class_key doesn't 
contribute much to the lockdep code. I am not against this change, but 
it is up others to decide if they will take the patch.

Cheers,
Longman

>
>> Cheers,
>> Longman
>>
>>> 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);
>>>      static inline void
>>>    lockdep_init_map_waits(struct lockdep_map *lock, const char *name,
>>> -               struct lock_class_key *key, int subclass, u8 inner, u8 outer)
>>> +               const struct lock_class_key *key, int subclass,
>>> +               u8 inner, u8 outer)
>>>    {
>>>        lockdep_init_map_type(lock, name, key, subclass, inner, outer, LD_LOCK_NORMAL);
>>>    }
>>>      static inline void
>>>    lockdep_init_map_wait(struct lockdep_map *lock, const char *name,
>>> -              struct lock_class_key *key, int subclass, u8 inner)
>>> +              const struct lock_class_key *key, int subclass, u8 inner)
>>>    {
>>>        lockdep_init_map_waits(lock, name, key, subclass, inner, LD_WAIT_INV);
>>>    }
>>>      static inline void lockdep_init_map(struct lockdep_map *lock, const char *name,
>>> -                 struct lock_class_key *key, int subclass)
>>> +                    const struct lock_class_key *key, int subclass)
>>>    {
>>>        lockdep_init_map_wait(lock, name, key, subclass, LD_WAIT_INV);
>>>    }
>>> @@ -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);
>>>      #define lock_set_novalidate_class(l, n, i) \
>>>        lock_set_class(l, n, &__lockdep_no_validate__, 0, i)
>>> diff --git a/include/linux/lockdep_types.h b/include/linux/lockdep_types.h
>>> index eae115a26..0d3df9019 100644
>>> --- a/include/linux/lockdep_types.h
>>> +++ b/include/linux/lockdep_types.h
>>> @@ -184,7 +184,7 @@ void clear_lock_stats(struct lock_class *class);
>>>     * This is embedded into specific lock instances:
>>>     */
>>>    struct lockdep_map {
>>> -    struct lock_class_key        *key;
>>> +    const struct lock_class_key        *key;
>>>        struct lock_class        *class_cache[NR_LOCKDEP_CACHING_CLASSES];
>>>        const char            *name;
>>>        u8                wait_type_outer; /* can be taken in this context */
>>> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
>>> index f13883162..fe1415260 100644
>>> --- a/kernel/locking/lockdep.c
>>> +++ b/kernel/locking/lockdep.c
>>> @@ -888,7 +888,7 @@ static int count_matching_names(struct lock_class *new_class)
>>>    static noinstr struct lock_class *
>>>    look_up_lock_class(const struct lockdep_map *lock, unsigned int subclass)
>>>    {
>>> -    struct lockdep_subclass_key *key;
>>> +    const struct lockdep_subclass_key *key;
>>>        struct hlist_head *hash_head;
>>>        struct lock_class *class;
>>>    @@ -1286,7 +1286,7 @@ static bool is_dynamic_key(const struct lock_class_key *key)
>>>    static struct lock_class *
>>>    register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
>>>    {
>>> -    struct lockdep_subclass_key *key;
>>> +    const struct lockdep_subclass_key *key;
>>>        struct hlist_head *hash_head;
>>>        struct lock_class *class;
>>>        int idx;
>>> @@ -4937,8 +4937,8 @@ static inline int check_wait_context(struct task_struct *curr,
>>>     * Initialize a lock instance's lock-class mapping info:
>>>     */
>>>    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)
>>> +               const struct lock_class_key *key, int subclass,
>>> +               u8 inner, u8 outer, u8 lock_type)
>>>    {
>>>        int i;
>>>    @@ -5408,7 +5408,7 @@ static int reacquire_held_locks(struct task_struct *curr, unsigned int depth,
>>>      static int
>>>    __lock_set_class(struct lockdep_map *lock, const char *name,
>>> -         struct lock_class_key *key, unsigned int subclass,
>>> +         const struct lock_class_key *key, unsigned int subclass,
>>>             unsigned long ip)
>>>    {
>>>        struct task_struct *curr = current;
>>> @@ -5733,7 +5733,7 @@ static noinstr void check_flags(unsigned long flags)
>>>    }
>>>      void lock_set_class(struct lockdep_map *lock, const char *name,
>>> -            struct lock_class_key *key, unsigned int subclass,
>>> +            const struct lock_class_key *key, unsigned int subclass,
>>>                unsigned long ip)
>>>    {
>>>        unsigned long flags;

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

[Peter Zijlstra]

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?

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

[Heiner Kallweit]

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."