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

On May 11, 2026, at 20:22, David Hildenbrand (Arm) [off-list ref] wrote:

On 5/11/26 13:18, Muchun Song wrote:

quoted

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.

[...]

quoted

   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.

quoted

+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