Re: [PATCH] PCI: endpoint: pci-epf-test: NULL check dma channels before release

[Damien Le Moal <dlemoal@kernel.org>]

On 9/12/25 18:59, Shinichiro Kawasaki wrote:
> On Sep 12, 2025 / 16:31, Damien Le Moal wrote:
>> On 9/12/25 16:11, Shin'ichiro Kawasaki wrote:
>>> When endpoint controller driver is immature, the fields dma_chan_tx and
>>> dma_chan_rx of the struct pci_epf_test could be NULL even after epf
>>> initialization. However, pci_epf_test_clean_dma_chan() assumes that they
>>> are always non-NULL valid values, and causes kernel panic when the
>>> fields are NULL. To avoid the kernel panic, NULL check the fields before
>>> release.
>>>
>>> Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
>>> ---
>>>  drivers/pci/endpoint/functions/pci-epf-test.c | 17 +++++++++++------
>>>  1 file changed, 11 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/drivers/pci/endpoint/functions/pci-epf-test.c b/drivers/pci/endpoint/functions/pci-epf-test.c
>>> index e091193bd8a8..1c29d5dd4382 100644
>>> --- a/drivers/pci/endpoint/functions/pci-epf-test.c
>>> +++ b/drivers/pci/endpoint/functions/pci-epf-test.c
>>> @@ -301,15 +301,20 @@ static void pci_epf_test_clean_dma_chan(struct pci_epf_test *epf_test)
>>>  	if (!epf_test->dma_supported)
>>>  		return;
>>>  
>>> -	dma_release_channel(epf_test->dma_chan_tx);
>>> -	if (epf_test->dma_chan_tx == epf_test->dma_chan_rx) {
>>> +	if (epf_test->dma_chan_tx) {
>>> +		dma_release_channel(epf_test->dma_chan_tx);
>>> +		if (epf_test->dma_chan_tx == epf_test->dma_chan_rx) {
>>> +			epf_test->dma_chan_tx = NULL;
>>> +			epf_test->dma_chan_rx = NULL;
>>> +			return;
>>> +		}
>>>  		epf_test->dma_chan_tx = NULL;
>>> -		epf_test->dma_chan_rx = NULL;
>>> -		return;
>>>  	}
>>
>> Can we simplify here ?
> 
> I'm afraid, no,
> 
>>
>> 	if (epf_test->dma_chan_tx) {
>> 		dma_release_channel(epf_test->dma_chan_tx);
>> 		epf_test->dma_chan_tx = NULL;
> 
> because the line above affects the comparison below.

Arg... Of course ! Sorry about the noise.

> 
>> 		if (epf_test->dma_chan_tx == epf_test->dma_chan_rx) {
>> 			epf_test->dma_chan_rx = NULL;
>> 			return;
>> 		}
>> 	}
>>
>>>  
>>> -	dma_release_channel(epf_test->dma_chan_rx);
>>> -	epf_test->dma_chan_rx = NULL;
>>> +	if (epf_test->dma_chan_rx) {
>>> +		dma_release_channel(epf_test->dma_chan_rx);
>>> +		epf_test->dma_chan_rx = NULL;
>>> +	}
>>>  }
>>>  
>>>  static void pci_epf_test_print_rate(struct pci_epf_test *epf_test,
>>
>>
>> -- 
>> Damien Le Moal
>> Western Digital Research


-- 
Damien Le Moal
Western Digital Research