[PATCH v2 1/3] mm/memory_hotplug: fix memory block reference leak on remove

[Muchun Song <songmuchun@bytedance.com>]

remove_memory_blocks_and_altmaps() looks up each memory block with
find_memory_block(), which acquires a reference to the memory block
device.

That reference is never dropped on this path, resulting in a leaked
device reference when removing memory blocks and their altmaps. Drop
the reference after retrieving mem->altmap and clearing mem->altmap,
before removing the memory block device.

Fixes: 6b8f0798b85a ("mm/memory_hotplug: split memmap_on_memory requests across memblocks")
Cc: stable@vger.kernel.org
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Oscar Salvador <osalvador@suse.de>
---
v1->v2:
- Add Acked-by from Oscar.
- I didn't add memory_block_get_by_id/memory_block_put because this
  is a pure bugfix series. I will send that separate cleanup after
  the bugfixes have been merged.
---
 mm/memory_hotplug.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 2a943ec57c85..40c7915dabe0 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1422,6 +1422,8 @@ static void remove_memory_blocks_and_altmaps(u64 start, u64 size)
 
 		altmap = mem->altmap;
 		mem->altmap = NULL;
+		/* drop the ref. we got via find_memory_block() */
+		put_device(&mem->dev);
 
 		remove_memory_block_devices(cur_start, memblock_size);
 
-- 
2.20.1