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SubjectRe: [PATCH] mm: memory_hotplug: use put_device() if device_register fail
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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.cs@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

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