Re: [PATCH] mm: memory_hotplug: use put_device() if device_register fail

[arvindY]

On Friday 27 April 2018 08:26 PM, Michal Hocko wrote:
On Thu 26-04-18 21:12:09, Arvind Yadav wrote:
if device_register() returned an error. Always use put_device()
to give up the initialized reference and release allocated memory.
Is this patch correct? The docummentation says
  * NOTE: _Never_ directly free @dev after calling this function, even
  * if it returned an error! Always use put_device() to give up your
  * reference instead.

but we do not have _our_ reference in this path AFAICS. Maybe this is
just a documentation issue? How have you tested this change btw.?
The document is correct. Here device_register() will initialize object by
making reference count as 1 and also increment reference count for device.

device_register() {
   device_initialize()->kobject_init()->kref_init() - initialize 
object( reference count = 1).
   device_add()->get_device() - increment reference count for device.
}

If device_register() will fail then we have to release the object by making
reference count 0. So we need to call put_object() which will release the
object and other resources like memory etc. so long as the reference
count is nonzero, the object continue to exist in memory.

I have not tested this peace of code. But I have tested other code which
is using Kboject.

~arvind

Signed-off-by: Arvind Yadav <arvind.yadav...@gmail.com>
---
  drivers/base/memory.c | 8 +++++++-
  1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index bffe861..f5e5601 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -649,13 +649,19 @@ static const struct attribute_group 
*memory_memblk_attr_groups[] = {
  static
  int register_memory(struct memory_block *memory)
  {
+       int ret;
+
        memory->dev.bus = &memory_subsys;
        memory->dev.id = memory->start_section_nr / sections_per_block;
        memory->dev.release = memory_block_release;
        memory->dev.groups = memory_memblk_attr_groups;
        memory->dev.offline = memory->state == MEM_OFFLINE;
  
-	return device_register(&memory->dev);
+       ret = device_register(&memory->dev);
+       if (ret)
+               put_device(&memory->dev);
+
+       return ret;
  }
  
  static int init_memory_block(struct memory_block **memory,
--
2.7.4