linux-kernel - Re: [PATCH] Revert "PCI: Fix reference leak in pci_register_host

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Message-ID: <7d2fe444-7e6a-4633-a489-55bba916a7cc@huawei.com>
Date: Mon, 14 Apr 2025 10:41:12 +0800
From: "liwei (JK)" <liwei728@...wei.com>
To: Su Hui <suhui@...china.com>
CC: <linux-kernel@...r.kernel.org>, <make24@...as.ac.cn>,
	<bhelgaas@...gle.com>, <linux-pci@...r.kernel.org>,
	<bobo.shaobowang@...wei.com>, <wangxiongfeng2@...wei.com>
Subject: Re: [PATCH] Revert "PCI: Fix reference leak in
 pci_register_host_bridge()"



在 2025/4/12 11:18, liwei (JK) 写道:
> 
> 
> 在 2025/4/10 19:19, Su Hui 写道:
>> On 2025/4/10 11:28, Xiangwei Li wrote:
>>> This reverts commit 804443c1f27883926de94c849d91f5b7d7d696e9.
>>>
>>> The newly added logic incorrectly sets bus_registered to true even when
>>> device_register returns an error, this is incorrect.
>>>
>>> When device_register fails, there is no need to release the reference 
>>> count,
>> I think you missed some thing about device_register(). This patch is 
>> wrong.
>>
>> device_register()
>>      -> device_initialize()
>>                -> kobject_init()
>>                      -> kobject_init_internal()
>>                          -> kref_init(&kobj->kref);  //set 
>> kref->refcount to 1
>>                             ^^^^^^^^^^^^^^^^^^^^^
>>
> Sorry, I missed the initialization of refcount in device_initialize,
> but I’m confused about the branch logic for bus_registered. Why isn’t
> free(bus) executed when bus_registered == true? My understanding is
> that the kobject_cleanup operation triggered when refcount reaches zero
> does not clean up the allocated bus. Could you clarify this further?
> 
> Thanks,
> Xiangwei Li
Hi Su,

Thank you very much for your explanation. Based on your response and an
analysis of the corresponding release paths, this confirms that the
issue I previously raised does not exist in your patch.

Release path:
  kobject_cleanup
	->device_release  // device_ktype.device_release
		->release_pcibus_dev  // pcibus_class.release_pcibus_dev
			->kfree(pci_bus)   // free(bus)

Thanks,
Xiangwei Li

>> device_register() only  fails when device_add() fails, and 
>> kerf->refcount can be 1
>> at this time ,  so we need to call put_deivce() to release  memory.
>>> and there are no direct error-handling operations following its 
>>> execution.
>>>
>>> Therefore, this patch is meaningless and should be reverted.
>>>
>>> Fixes: 804443c1f278 ("PCI: Fix reference leak in 
>>> pci_register_host_bridge()")
>>> Signed-off-by: Xiangwei Li <liwei728@...wei.com>
>>> Signed-off-by: Xiongfeng Wang <wangxiongfeng2@...wei.com>
>>
>