Re: [PATCH] drivers/base/memory: make memory block get/put explicit

[Muchun Song <muchun.song@linux.dev>]

> On May 11, 2026, at 20:22, David Hildenbrand (Arm) <david@kernel.org> wrote:
> 
> On 5/11/26 13:18, Muchun Song wrote:
>> Rename the memory block lookup helper to make the acquired reference
>> explicit, add memory_block_put() to wrap put_device(), and collapse the
>> redundant section-number wrapper into a single block-id based lookup
>> interface.
>> 
>> This makes it clearer to callers that a successful lookup holds a
>> reference that must be dropped, reducing the chance of forgetting the
>> matching put and leaking the memory block device reference.
> 
> Better mention some of the other changes here, like removing find_memory_block().

Will do.

> 
> [...]
> 
>>    unlock_device_hotplug();
>> diff --git a/include/linux/memory.h b/include/linux/memory.h
>> index 5bb5599c6b2b..29edef1f975c 100644
>> --- a/include/linux/memory.h
>> +++ b/include/linux/memory.h
>> @@ -158,7 +158,11 @@ int create_memory_block_devices(unsigned long start, unsigned long size,
>> void remove_memory_block_devices(unsigned long start, unsigned long size);
>> extern void memory_dev_init(void);
>> extern int memory_notify(enum memory_block_state state, void *v);
>> -extern struct memory_block *find_memory_block(unsigned long section_nr);
>> +extern struct memory_block *memory_block_get(unsigned long block_id);
> 
> While at it, please drop the "extern".

OK.

> 
>> +static inline void memory_block_put(struct memory_block *mem)
>> +{
>> +    put_device(&mem->dev);
>> +}
>> typedef int (*walk_memory_blocks_func_t)(struct memory_block *, void *);
>> extern int walk_memory_blocks(unsigned long start, unsigned long size,
>>                  void *arg, walk_memory_blocks_func_t func);
>> @@ -171,7 +175,6 @@ struct memory_group *memory_group_find_by_id(int mgid);
>> typedef int (*walk_memory_groups_func_t)(struct memory_group *, void *);
>> int walk_dynamic_memory_groups(int nid, walk_memory_groups_func_t func,
>>                   struct memory_group *excluded, void *arg);
>> -struct memory_block *find_memory_block_by_id(unsigned long block_id);
>> #define hotplug_memory_notifier(fn, pri) ({        \
>>    static __meminitdata struct notifier_block fn##_mem_nb =\
>>        { .notifier_call = fn, .priority = pri };\
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index 462d8dcd636d..890c6453e887 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -1417,14 +1417,13 @@ static void remove_memory_blocks_and_altmaps(u64 start, u64 size)
>>        struct vmem_altmap *altmap = NULL;
>>        struct memory_block *mem;
>> 
>> -        mem = find_memory_block(pfn_to_section_nr(PFN_DOWN(cur_start)));
>> +        mem = memory_block_get(phys_to_block_id(cur_start));
>>        if (WARN_ON_ONCE(!mem))
>>            continue;
>> 
>>        altmap = mem->altmap;
>>        mem->altmap = NULL;
>> -        /* drop the ref. we got via find_memory_block() */
>> -        put_device(&mem->dev);
>> +        memory_block_put(mem);
> 
> Would guards come in handy here?

You mean to introduce something like:

scoped_guard(memory_block, id) {
}

Right? If yes, I will give it a try.

> 
> In general
> 
> Acked-by: David Hildenbrand (Arm) <david@kernel.org>

Thanks.

Muchun

> 
> --
> Cheers,
> 
> David