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

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

[Muchun Song]

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.

Link: https://lore.kernel.org/linux-mm/7887915D-E598-42B3-9AFE-BFFBACE8DE2D@linux.dev/#t
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 .../platforms/pseries/hotplug-memory.c        | 14 ++-----
 drivers/base/memory.c                         | 38 +++++++------------
 drivers/base/node.c                           |  4 +-
 drivers/s390/char/sclp_mem.c                  | 17 ++++-----
 include/linux/memory.h                        |  7 +++-
 mm/memory_hotplug.c                           |  5 +--
 6 files changed, 35 insertions(+), 50 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c
index 75f85a5da981..94f3b57054b6 100644
--- a/arch/powerpc/platforms/pseries/hotplug-memory.c
+++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
@@ -164,13 +164,7 @@ static int update_lmb_associativity_index(struct drmem_lmb *lmb)
 
 static struct memory_block *lmb_to_memblock(struct drmem_lmb *lmb)
 {
-	unsigned long section_nr;
-	struct memory_block *mem_block;
-
-	section_nr = pfn_to_section_nr(PFN_DOWN(lmb->base_addr));
-
-	mem_block = find_memory_block(section_nr);
-	return mem_block;
+	return memory_block_get(phys_to_block_id(lmb->base_addr));
 }
 
 static int get_lmb_range(u32 drc_index, int n_lmbs,
@@ -220,7 +214,7 @@ static int dlpar_change_lmb_state(struct drmem_lmb *lmb, bool online)
 	else
 		rc = 0;
 
-	put_device(&mem_block->dev);
+	memory_block_put(mem_block);
 
 	return rc;
 }
@@ -319,12 +313,12 @@ static int dlpar_remove_lmb(struct drmem_lmb *lmb)
 
 	rc = dlpar_offline_lmb(lmb);
 	if (rc) {
-		put_device(&mem_block->dev);
+		memory_block_put(mem_block);
 		return rc;
 	}
 
 	__remove_memory(lmb->base_addr, memory_block_size);
-	put_device(&mem_block->dev);
+	memory_block_put(mem_block);
 
 	/* Update memory regions for memory remove */
 	memblock_remove(lmb->base_addr, memory_block_size);
diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index 11d57cfa8d72..5b5d41089e81 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -649,7 +649,7 @@ int __weak arch_get_memory_phys_device(unsigned long start_pfn)
  *
  * Called under device_hotplug_lock.
  */
-struct memory_block *find_memory_block_by_id(unsigned long block_id)
+struct memory_block *memory_block_get(unsigned long block_id)
 {
 	struct memory_block *mem;
 
@@ -659,16 +659,6 @@ struct memory_block *find_memory_block_by_id(unsigned long block_id)
 	return mem;
 }
 
-/*
- * Called under device_hotplug_lock.
- */
-struct memory_block *find_memory_block(unsigned long section_nr)
-{
-	unsigned long block_id = memory_block_id(section_nr);
-
-	return find_memory_block_by_id(block_id);
-}
-
 static struct attribute *memory_memblk_attrs[] = {
 	&dev_attr_phys_index.attr,
 	&dev_attr_state.attr,
@@ -701,7 +691,7 @@ static int __add_memory_block(struct memory_block *memory)
 
 	ret = device_register(&memory->dev);
 	if (ret) {
-		put_device(&memory->dev);
+		memory_block_put(memory);
 		return ret;
 	}
 	ret = xa_err(xa_store(&memory_blocks, memory->dev.id, memory,
@@ -795,9 +785,9 @@ static int add_memory_block(unsigned long block_id, int nid, unsigned long state
 	struct memory_block *mem;
 	int ret = 0;
 
-	mem = find_memory_block_by_id(block_id);
+	mem = memory_block_get(block_id);
 	if (mem) {
-		put_device(&mem->dev);
+		memory_block_put(mem);
 		return -EEXIST;
 	}
 	mem = kzalloc_obj(*mem);
@@ -845,8 +835,8 @@ static void remove_memory_block(struct memory_block *memory)
 		memory->group = NULL;
 	}
 
-	/* drop the ref. we got via find_memory_block() */
-	put_device(&memory->dev);
+	/* drop the ref. we got via memory_block_get() */
+	memory_block_put(memory);
 	device_unregister(&memory->dev);
 }
 
@@ -880,7 +870,7 @@ int create_memory_block_devices(unsigned long start, unsigned long size,
 		end_block_id = block_id;
 		for (block_id = start_block_id; block_id != end_block_id;
 		     block_id++) {
-			mem = find_memory_block_by_id(block_id);
+			mem = memory_block_get(block_id);
 			if (WARN_ON_ONCE(!mem))
 				continue;
 			remove_memory_block(mem);
@@ -908,7 +898,7 @@ void remove_memory_block_devices(unsigned long start, unsigned long size)
 		return;
 
 	for (block_id = start_block_id; block_id != end_block_id; block_id++) {
-		mem = find_memory_block_by_id(block_id);
+		mem = memory_block_get(block_id);
 		if (WARN_ON_ONCE(!mem))
 			continue;
 		num_poisoned_pages_sub(-1UL, memblk_nr_poison(mem));
@@ -1015,12 +1005,12 @@ int walk_memory_blocks(unsigned long start, unsigned long size,
 		return 0;
 
 	for (block_id = start_block_id; block_id <= end_block_id; block_id++) {
-		mem = find_memory_block_by_id(block_id);
+		mem = memory_block_get(block_id);
 		if (!mem)
 			continue;
 
 		ret = func(mem, arg);
-		put_device(&mem->dev);
+		memory_block_put(mem);
 		if (ret)
 			break;
 	}
@@ -1228,22 +1218,22 @@ int walk_dynamic_memory_groups(int nid, walk_memory_groups_func_t func,
 void memblk_nr_poison_inc(unsigned long pfn)
 {
 	const unsigned long block_id = pfn_to_block_id(pfn);
-	struct memory_block *mem = find_memory_block_by_id(block_id);
+	struct memory_block *mem = memory_block_get(block_id);
 
 	if (mem) {
 		atomic_long_inc(&mem->nr_hwpoison);
-		put_device(&mem->dev);
+		memory_block_put(mem);
 	}
 }
 
 void memblk_nr_poison_sub(unsigned long pfn, long i)
 {
 	const unsigned long block_id = pfn_to_block_id(pfn);
-	struct memory_block *mem = find_memory_block_by_id(block_id);
+	struct memory_block *mem = memory_block_get(block_id);
 
 	if (mem) {
 		atomic_long_sub(i, &mem->nr_hwpoison);
-		put_device(&mem->dev);
+		memory_block_put(mem);
 	}
 }
 
diff --git a/drivers/base/node.c b/drivers/base/node.c
index 126f66aa2c3e..b3333ca92090 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -847,13 +847,13 @@ static void register_memory_blocks_under_nodes(void)
 		for (block_id = start_block_id; block_id <= end_block_id; block_id++) {
 			struct memory_block *mem;
 
-			mem = find_memory_block_by_id(block_id);
+			mem = memory_block_get(block_id);
 			if (!mem)
 				continue;
 
 			memory_block_add_nid_early(mem, nid);
 			do_register_memory_block_under_node(nid, mem);
-			put_device(&mem->dev);
+			memory_block_put(mem);
 		}
 
 	}
diff --git a/drivers/s390/char/sclp_mem.c b/drivers/s390/char/sclp_mem.c
index 78c054e26d17..6df1926d4c62 100644
--- a/drivers/s390/char/sclp_mem.c
+++ b/drivers/s390/char/sclp_mem.c
@@ -204,7 +204,7 @@ static ssize_t sclp_config_mem_store(struct kobject *kobj, struct kobj_attribute
 	addr = sclp_mem->id * block_size;
 	/*
 	 * Hold device_hotplug_lock when adding/removing memory blocks.
-	 * Additionally, also protect calls to find_memory_block() and
+	 * Additionally, also protect calls to memory_block_get() and
 	 * sclp_attach_storage().
 	 */
 	rc = lock_device_hotplug_sysfs();
@@ -231,20 +231,19 @@ static ssize_t sclp_config_mem_store(struct kobject *kobj, struct kobj_attribute
 			sclp_mem_change_state(addr, block_size, 0);
 			goto out_unlock;
 		}
-		mem = find_memory_block(pfn_to_section_nr(PFN_DOWN(addr)));
-		put_device(&mem->dev);
+		mem = memory_block_get(phys_to_block_id(addr));
+		memory_block_put(mem);
 		WRITE_ONCE(sclp_mem->config, 1);
 	} else {
 		if (!sclp_mem->config)
 			goto out_unlock;
-		mem = find_memory_block(pfn_to_section_nr(PFN_DOWN(addr)));
+		mem = memory_block_get(phys_to_block_id(addr));
 		if (mem->state != MEM_OFFLINE) {
-			put_device(&mem->dev);
+			memory_block_put(mem);
 			rc = -EBUSY;
 			goto out_unlock;
 		}
-		/* drop the ref just got via find_memory_block() */
-		put_device(&mem->dev);
+		memory_block_put(mem);
 		sclp_mem_change_state(addr, block_size, 0);
 		__remove_memory(addr, block_size);
 #ifdef CONFIG_KASAN
@@ -294,11 +293,11 @@ static ssize_t sclp_memmap_on_memory_store(struct kobject *kobj, struct kobj_att
 		return rc;
 	block_size = memory_block_size_bytes();
 	sclp_mem = container_of(kobj, struct sclp_mem, kobj);
-	mem = find_memory_block(pfn_to_section_nr(PFN_DOWN(sclp_mem->id * block_size)));
+	mem = memory_block_get(phys_to_block_id(sclp_mem->id * block_size));
 	if (!mem) {
 		WRITE_ONCE(sclp_mem->memmap_on_memory, value);
 	} else {
-		put_device(&mem->dev);
+		memory_block_put(mem);
 		rc = -EBUSY;
 	}
 	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);
+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);
 
 		remove_memory_block_devices(cur_start, memblock_size);
 

base-commit: e98d21c170b01ddef366f023bbfcf6b31509fa83
-- 
2.54.0

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

[Michal Hocko]

On Mon 11-05-26 19:18:00, 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.
> 
> Link: https://lore.kernel.org/linux-mm/7887915D-E598-42B3-9AFE-BFFBACE8DE2D@linux.dev/#t
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>

Acked-by: Michal Hocko <mhocko@suse.com>
Thanks!

> ---
>  .../platforms/pseries/hotplug-memory.c        | 14 ++-----
>  drivers/base/memory.c                         | 38 +++++++------------
>  drivers/base/node.c                           |  4 +-
>  drivers/s390/char/sclp_mem.c                  | 17 ++++-----
>  include/linux/memory.h                        |  7 +++-
>  mm/memory_hotplug.c                           |  5 +--
>  6 files changed, 35 insertions(+), 50 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c
> index 75f85a5da981..94f3b57054b6 100644
> --- a/arch/powerpc/platforms/pseries/hotplug-memory.c
> +++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
> @@ -164,13 +164,7 @@ static int update_lmb_associativity_index(struct drmem_lmb *lmb)
>  
>  static struct memory_block *lmb_to_memblock(struct drmem_lmb *lmb)
>  {
> -	unsigned long section_nr;
> -	struct memory_block *mem_block;
> -
> -	section_nr = pfn_to_section_nr(PFN_DOWN(lmb->base_addr));
> -
> -	mem_block = find_memory_block(section_nr);
> -	return mem_block;
> +	return memory_block_get(phys_to_block_id(lmb->base_addr));
>  }
>  
>  static int get_lmb_range(u32 drc_index, int n_lmbs,
> @@ -220,7 +214,7 @@ static int dlpar_change_lmb_state(struct drmem_lmb *lmb, bool online)
>  	else
>  		rc = 0;
>  
> -	put_device(&mem_block->dev);
> +	memory_block_put(mem_block);
>  
>  	return rc;
>  }
> @@ -319,12 +313,12 @@ static int dlpar_remove_lmb(struct drmem_lmb *lmb)
>  
>  	rc = dlpar_offline_lmb(lmb);
>  	if (rc) {
> -		put_device(&mem_block->dev);
> +		memory_block_put(mem_block);
>  		return rc;
>  	}
>  
>  	__remove_memory(lmb->base_addr, memory_block_size);
> -	put_device(&mem_block->dev);
> +	memory_block_put(mem_block);
>  
>  	/* Update memory regions for memory remove */
>  	memblock_remove(lmb->base_addr, memory_block_size);
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 11d57cfa8d72..5b5d41089e81 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -649,7 +649,7 @@ int __weak arch_get_memory_phys_device(unsigned long start_pfn)
>   *
>   * Called under device_hotplug_lock.
>   */
> -struct memory_block *find_memory_block_by_id(unsigned long block_id)
> +struct memory_block *memory_block_get(unsigned long block_id)
>  {
>  	struct memory_block *mem;
>  
> @@ -659,16 +659,6 @@ struct memory_block *find_memory_block_by_id(unsigned long block_id)
>  	return mem;
>  }
>  
> -/*
> - * Called under device_hotplug_lock.
> - */
> -struct memory_block *find_memory_block(unsigned long section_nr)
> -{
> -	unsigned long block_id = memory_block_id(section_nr);
> -
> -	return find_memory_block_by_id(block_id);
> -}
> -
>  static struct attribute *memory_memblk_attrs[] = {
>  	&dev_attr_phys_index.attr,
>  	&dev_attr_state.attr,
> @@ -701,7 +691,7 @@ static int __add_memory_block(struct memory_block *memory)
>  
>  	ret = device_register(&memory->dev);
>  	if (ret) {
> -		put_device(&memory->dev);
> +		memory_block_put(memory);
>  		return ret;
>  	}
>  	ret = xa_err(xa_store(&memory_blocks, memory->dev.id, memory,
> @@ -795,9 +785,9 @@ static int add_memory_block(unsigned long block_id, int nid, unsigned long state
>  	struct memory_block *mem;
>  	int ret = 0;
>  
> -	mem = find_memory_block_by_id(block_id);
> +	mem = memory_block_get(block_id);
>  	if (mem) {
> -		put_device(&mem->dev);
> +		memory_block_put(mem);
>  		return -EEXIST;
>  	}
>  	mem = kzalloc_obj(*mem);
> @@ -845,8 +835,8 @@ static void remove_memory_block(struct memory_block *memory)
>  		memory->group = NULL;
>  	}
>  
> -	/* drop the ref. we got via find_memory_block() */
> -	put_device(&memory->dev);
> +	/* drop the ref. we got via memory_block_get() */
> +	memory_block_put(memory);
>  	device_unregister(&memory->dev);
>  }
>  
> @@ -880,7 +870,7 @@ int create_memory_block_devices(unsigned long start, unsigned long size,
>  		end_block_id = block_id;
>  		for (block_id = start_block_id; block_id != end_block_id;
>  		     block_id++) {
> -			mem = find_memory_block_by_id(block_id);
> +			mem = memory_block_get(block_id);
>  			if (WARN_ON_ONCE(!mem))
>  				continue;
>  			remove_memory_block(mem);
> @@ -908,7 +898,7 @@ void remove_memory_block_devices(unsigned long start, unsigned long size)
>  		return;
>  
>  	for (block_id = start_block_id; block_id != end_block_id; block_id++) {
> -		mem = find_memory_block_by_id(block_id);
> +		mem = memory_block_get(block_id);
>  		if (WARN_ON_ONCE(!mem))
>  			continue;
>  		num_poisoned_pages_sub(-1UL, memblk_nr_poison(mem));
> @@ -1015,12 +1005,12 @@ int walk_memory_blocks(unsigned long start, unsigned long size,
>  		return 0;
>  
>  	for (block_id = start_block_id; block_id <= end_block_id; block_id++) {
> -		mem = find_memory_block_by_id(block_id);
> +		mem = memory_block_get(block_id);
>  		if (!mem)
>  			continue;
>  
>  		ret = func(mem, arg);
> -		put_device(&mem->dev);
> +		memory_block_put(mem);
>  		if (ret)
>  			break;
>  	}
> @@ -1228,22 +1218,22 @@ int walk_dynamic_memory_groups(int nid, walk_memory_groups_func_t func,
>  void memblk_nr_poison_inc(unsigned long pfn)
>  {
>  	const unsigned long block_id = pfn_to_block_id(pfn);
> -	struct memory_block *mem = find_memory_block_by_id(block_id);
> +	struct memory_block *mem = memory_block_get(block_id);
>  
>  	if (mem) {
>  		atomic_long_inc(&mem->nr_hwpoison);
> -		put_device(&mem->dev);
> +		memory_block_put(mem);
>  	}
>  }
>  
>  void memblk_nr_poison_sub(unsigned long pfn, long i)
>  {
>  	const unsigned long block_id = pfn_to_block_id(pfn);
> -	struct memory_block *mem = find_memory_block_by_id(block_id);
> +	struct memory_block *mem = memory_block_get(block_id);
>  
>  	if (mem) {
>  		atomic_long_sub(i, &mem->nr_hwpoison);
> -		put_device(&mem->dev);
> +		memory_block_put(mem);
>  	}
>  }
>  
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 126f66aa2c3e..b3333ca92090 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -847,13 +847,13 @@ static void register_memory_blocks_under_nodes(void)
>  		for (block_id = start_block_id; block_id <= end_block_id; block_id++) {
>  			struct memory_block *mem;
>  
> -			mem = find_memory_block_by_id(block_id);
> +			mem = memory_block_get(block_id);
>  			if (!mem)
>  				continue;
>  
>  			memory_block_add_nid_early(mem, nid);
>  			do_register_memory_block_under_node(nid, mem);
> -			put_device(&mem->dev);
> +			memory_block_put(mem);
>  		}
>  
>  	}
> diff --git a/drivers/s390/char/sclp_mem.c b/drivers/s390/char/sclp_mem.c
> index 78c054e26d17..6df1926d4c62 100644
> --- a/drivers/s390/char/sclp_mem.c
> +++ b/drivers/s390/char/sclp_mem.c
> @@ -204,7 +204,7 @@ static ssize_t sclp_config_mem_store(struct kobject *kobj, struct kobj_attribute
>  	addr = sclp_mem->id * block_size;
>  	/*
>  	 * Hold device_hotplug_lock when adding/removing memory blocks.
> -	 * Additionally, also protect calls to find_memory_block() and
> +	 * Additionally, also protect calls to memory_block_get() and
>  	 * sclp_attach_storage().
>  	 */
>  	rc = lock_device_hotplug_sysfs();
> @@ -231,20 +231,19 @@ static ssize_t sclp_config_mem_store(struct kobject *kobj, struct kobj_attribute
>  			sclp_mem_change_state(addr, block_size, 0);
>  			goto out_unlock;
>  		}
> -		mem = find_memory_block(pfn_to_section_nr(PFN_DOWN(addr)));
> -		put_device(&mem->dev);
> +		mem = memory_block_get(phys_to_block_id(addr));
> +		memory_block_put(mem);
>  		WRITE_ONCE(sclp_mem->config, 1);
>  	} else {
>  		if (!sclp_mem->config)
>  			goto out_unlock;
> -		mem = find_memory_block(pfn_to_section_nr(PFN_DOWN(addr)));
> +		mem = memory_block_get(phys_to_block_id(addr));
>  		if (mem->state != MEM_OFFLINE) {
> -			put_device(&mem->dev);
> +			memory_block_put(mem);
>  			rc = -EBUSY;
>  			goto out_unlock;
>  		}
> -		/* drop the ref just got via find_memory_block() */
> -		put_device(&mem->dev);
> +		memory_block_put(mem);
>  		sclp_mem_change_state(addr, block_size, 0);
>  		__remove_memory(addr, block_size);
>  #ifdef CONFIG_KASAN
> @@ -294,11 +293,11 @@ static ssize_t sclp_memmap_on_memory_store(struct kobject *kobj, struct kobj_att
>  		return rc;
>  	block_size = memory_block_size_bytes();
>  	sclp_mem = container_of(kobj, struct sclp_mem, kobj);
> -	mem = find_memory_block(pfn_to_section_nr(PFN_DOWN(sclp_mem->id * block_size)));
> +	mem = memory_block_get(phys_to_block_id(sclp_mem->id * block_size));
>  	if (!mem) {
>  		WRITE_ONCE(sclp_mem->memmap_on_memory, value);
>  	} else {
> -		put_device(&mem->dev);
> +		memory_block_put(mem);
>  		rc = -EBUSY;
>  	}
>  	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);
> +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);
>  
>  		remove_memory_block_devices(cur_start, memblock_size);
>  
> 
> base-commit: e98d21c170b01ddef366f023bbfcf6b31509fa83
> -- 
> 2.54.0

-- 
Michal Hocko
SUSE Labs

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

[Oscar Salvador]

On Mon, May 11, 2026 at 07:18:00PM +0800, 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.
> 
> Link: https://lore.kernel.org/linux-mm/7887915D-E598-42B3-9AFE-BFFBACE8DE2D@linux.dev/#t
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>

Acked-by: Oscar Salvador <osalvador@suse.de>

Thanks, it looks more solid to me!
 

-- 
Oscar Salvador
SUSE Labs

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

[David Hildenbrand (Arm)]

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().

[...]

>  	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".

> +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?

In general

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

-- 
Cheers,

David

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

[Muchun Song]

> 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

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

[Lorenzo Stoakes]

On Mon, May 11, 2026 at 07:18:00PM +0800, 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.

As David said, let's reference more of what you've done in the various
refactorings.

>
> Link: https://lore.kernel.org/linux-mm/7887915D-E598-42B3-9AFE-BFFBACE8DE2D@linux.dev/#t
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>

LGTM overall, so:

Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>

> ---
>  .../platforms/pseries/hotplug-memory.c        | 14 ++-----
>  drivers/base/memory.c                         | 38 +++++++------------
>  drivers/base/node.c                           |  4 +-
>  drivers/s390/char/sclp_mem.c                  | 17 ++++-----
>  include/linux/memory.h                        |  7 +++-
>  mm/memory_hotplug.c                           |  5 +--
>  6 files changed, 35 insertions(+), 50 deletions(-)
>
> diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c
> index 75f85a5da981..94f3b57054b6 100644
> --- a/arch/powerpc/platforms/pseries/hotplug-memory.c
> +++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
> @@ -164,13 +164,7 @@ static int update_lmb_associativity_index(struct drmem_lmb *lmb)
>
>  static struct memory_block *lmb_to_memblock(struct drmem_lmb *lmb)
>  {
> -	unsigned long section_nr;
> -	struct memory_block *mem_block;
> -
> -	section_nr = pfn_to_section_nr(PFN_DOWN(lmb->base_addr));
> -
> -	mem_block = find_memory_block(section_nr);
> -	return mem_block;
> +	return memory_block_get(phys_to_block_id(lmb->base_addr));

Ah nice I see this does the equivalent via phys_to_block_id() and
pfn_to_block_id() so that's a nice cleanup.

>  }
>
>  static int get_lmb_range(u32 drc_index, int n_lmbs,
> @@ -220,7 +214,7 @@ static int dlpar_change_lmb_state(struct drmem_lmb *lmb, bool online)
>  	else
>  		rc = 0;
>
> -	put_device(&mem_block->dev);
> +	memory_block_put(mem_block);
>
>  	return rc;
>  }
> @@ -319,12 +313,12 @@ static int dlpar_remove_lmb(struct drmem_lmb *lmb)
>
>  	rc = dlpar_offline_lmb(lmb);
>  	if (rc) {
> -		put_device(&mem_block->dev);
> +		memory_block_put(mem_block);
>  		return rc;
>  	}
>
>  	__remove_memory(lmb->base_addr, memory_block_size);
> -	put_device(&mem_block->dev);
> +	memory_block_put(mem_block);
>
>  	/* Update memory regions for memory remove */
>  	memblock_remove(lmb->base_addr, memory_block_size);
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 11d57cfa8d72..5b5d41089e81 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -649,7 +649,7 @@ int __weak arch_get_memory_phys_device(unsigned long start_pfn)
>   *
>   * Called under device_hotplug_lock.
>   */
> -struct memory_block *find_memory_block_by_id(unsigned long block_id)
> +struct memory_block *memory_block_get(unsigned long block_id)
>  {
>  	struct memory_block *mem;
>
> @@ -659,16 +659,6 @@ struct memory_block *find_memory_block_by_id(unsigned long block_id)
>  	return mem;
>  }
>
> -/*
> - * Called under device_hotplug_lock.
> - */
> -struct memory_block *find_memory_block(unsigned long section_nr)
> -{
> -	unsigned long block_id = memory_block_id(section_nr);
> -
> -	return find_memory_block_by_id(block_id);
> -}
> -
>  static struct attribute *memory_memblk_attrs[] = {
>  	&dev_attr_phys_index.attr,
>  	&dev_attr_state.attr,
> @@ -701,7 +691,7 @@ static int __add_memory_block(struct memory_block *memory)
>
>  	ret = device_register(&memory->dev);
>  	if (ret) {
> -		put_device(&memory->dev);
> +		memory_block_put(memory);
>  		return ret;
>  	}
>  	ret = xa_err(xa_store(&memory_blocks, memory->dev.id, memory,
> @@ -795,9 +785,9 @@ static int add_memory_block(unsigned long block_id, int nid, unsigned long state
>  	struct memory_block *mem;
>  	int ret = 0;
>
> -	mem = find_memory_block_by_id(block_id);
> +	mem = memory_block_get(block_id);
>  	if (mem) {
> -		put_device(&mem->dev);
> +		memory_block_put(mem);
>  		return -EEXIST;
>  	}
>  	mem = kzalloc_obj(*mem);
> @@ -845,8 +835,8 @@ static void remove_memory_block(struct memory_block *memory)
>  		memory->group = NULL;
>  	}
>
> -	/* drop the ref. we got via find_memory_block() */
> -	put_device(&memory->dev);
> +	/* drop the ref. we got via memory_block_get() */
> +	memory_block_put(memory);
>  	device_unregister(&memory->dev);
>  }
>
> @@ -880,7 +870,7 @@ int create_memory_block_devices(unsigned long start, unsigned long size,
>  		end_block_id = block_id;
>  		for (block_id = start_block_id; block_id != end_block_id;
>  		     block_id++) {
> -			mem = find_memory_block_by_id(block_id);
> +			mem = memory_block_get(block_id);
>  			if (WARN_ON_ONCE(!mem))
>  				continue;
>  			remove_memory_block(mem);
> @@ -908,7 +898,7 @@ void remove_memory_block_devices(unsigned long start, unsigned long size)
>  		return;
>
>  	for (block_id = start_block_id; block_id != end_block_id; block_id++) {
> -		mem = find_memory_block_by_id(block_id);
> +		mem = memory_block_get(block_id);
>  		if (WARN_ON_ONCE(!mem))
>  			continue;
>  		num_poisoned_pages_sub(-1UL, memblk_nr_poison(mem));
> @@ -1015,12 +1005,12 @@ int walk_memory_blocks(unsigned long start, unsigned long size,
>  		return 0;
>
>  	for (block_id = start_block_id; block_id <= end_block_id; block_id++) {
> -		mem = find_memory_block_by_id(block_id);
> +		mem = memory_block_get(block_id);
>  		if (!mem)
>  			continue;
>
>  		ret = func(mem, arg);
> -		put_device(&mem->dev);
> +		memory_block_put(mem);
>  		if (ret)
>  			break;
>  	}
> @@ -1228,22 +1218,22 @@ int walk_dynamic_memory_groups(int nid, walk_memory_groups_func_t func,
>  void memblk_nr_poison_inc(unsigned long pfn)
>  {
>  	const unsigned long block_id = pfn_to_block_id(pfn);
> -	struct memory_block *mem = find_memory_block_by_id(block_id);
> +	struct memory_block *mem = memory_block_get(block_id);
>
>  	if (mem) {
>  		atomic_long_inc(&mem->nr_hwpoison);
> -		put_device(&mem->dev);
> +		memory_block_put(mem);
>  	}
>  }
>
>  void memblk_nr_poison_sub(unsigned long pfn, long i)
>  {
>  	const unsigned long block_id = pfn_to_block_id(pfn);
> -	struct memory_block *mem = find_memory_block_by_id(block_id);
> +	struct memory_block *mem = memory_block_get(block_id);
>
>  	if (mem) {
>  		atomic_long_sub(i, &mem->nr_hwpoison);
> -		put_device(&mem->dev);
> +		memory_block_put(mem);
>  	}
>  }
>
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 126f66aa2c3e..b3333ca92090 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -847,13 +847,13 @@ static void register_memory_blocks_under_nodes(void)
>  		for (block_id = start_block_id; block_id <= end_block_id; block_id++) {
>  			struct memory_block *mem;
>
> -			mem = find_memory_block_by_id(block_id);
> +			mem = memory_block_get(block_id);
>  			if (!mem)
>  				continue;
>
>  			memory_block_add_nid_early(mem, nid);
>  			do_register_memory_block_under_node(nid, mem);
> -			put_device(&mem->dev);
> +			memory_block_put(mem);
>  		}
>
>  	}
> diff --git a/drivers/s390/char/sclp_mem.c b/drivers/s390/char/sclp_mem.c
> index 78c054e26d17..6df1926d4c62 100644
> --- a/drivers/s390/char/sclp_mem.c
> +++ b/drivers/s390/char/sclp_mem.c
> @@ -204,7 +204,7 @@ static ssize_t sclp_config_mem_store(struct kobject *kobj, struct kobj_attribute
>  	addr = sclp_mem->id * block_size;
>  	/*
>  	 * Hold device_hotplug_lock when adding/removing memory blocks.
> -	 * Additionally, also protect calls to find_memory_block() and
> +	 * Additionally, also protect calls to memory_block_get() and
>  	 * sclp_attach_storage().
>  	 */
>  	rc = lock_device_hotplug_sysfs();
> @@ -231,20 +231,19 @@ static ssize_t sclp_config_mem_store(struct kobject *kobj, struct kobj_attribute
>  			sclp_mem_change_state(addr, block_size, 0);
>  			goto out_unlock;
>  		}
> -		mem = find_memory_block(pfn_to_section_nr(PFN_DOWN(addr)));
> -		put_device(&mem->dev);
> +		mem = memory_block_get(phys_to_block_id(addr));
> +		memory_block_put(mem);
>  		WRITE_ONCE(sclp_mem->config, 1);
>  	} else {
>  		if (!sclp_mem->config)
>  			goto out_unlock;
> -		mem = find_memory_block(pfn_to_section_nr(PFN_DOWN(addr)));
> +		mem = memory_block_get(phys_to_block_id(addr));
>  		if (mem->state != MEM_OFFLINE) {
> -			put_device(&mem->dev);
> +			memory_block_put(mem);
>  			rc = -EBUSY;
>  			goto out_unlock;
>  		}
> -		/* drop the ref just got via find_memory_block() */
> -		put_device(&mem->dev);
> +		memory_block_put(mem);
>  		sclp_mem_change_state(addr, block_size, 0);
>  		__remove_memory(addr, block_size);
>  #ifdef CONFIG_KASAN
> @@ -294,11 +293,11 @@ static ssize_t sclp_memmap_on_memory_store(struct kobject *kobj, struct kobj_att
>  		return rc;
>  	block_size = memory_block_size_bytes();
>  	sclp_mem = container_of(kobj, struct sclp_mem, kobj);
> -	mem = find_memory_block(pfn_to_section_nr(PFN_DOWN(sclp_mem->id * block_size)));
> +	mem = memory_block_get(phys_to_block_id(sclp_mem->id * block_size));
>  	if (!mem) {
>  		WRITE_ONCE(sclp_mem->memmap_on_memory, value);
>  	} else {
> -		put_device(&mem->dev);
> +		memory_block_put(mem);
>  		rc = -EBUSY;
>  	}
>  	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);
> +static inline void memory_block_put(struct memory_block *mem)

Yeah as David says, we remove extern's now as and when we touch that code :)

> +{
> +	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);
>
>  		remove_memory_block_devices(cur_start, memblock_size);
>
>
> base-commit: e98d21c170b01ddef366f023bbfcf6b31509fa83
> --
> 2.54.0
>