Re: Bad kfree of dma_parms in v5.7-rc5

[Tomi Valkeinen <tomi.valkeinen@ti.com>]

Hi Marek,

On 20/05/2020 12:13, Marek Szyprowski wrote:
> Hi Tomi,
> 
> On 20.05.2020 11:00, Tomi Valkeinen wrote:
>> Commit 9495b7e92f716ab2bd6814fab5e97ab4a39adfdd ("driver core:
>> platform: Initialize dma_parms for platform devices") v5.7-rc5 causes
>> at least some v4l2 platform drivers to break when freeing resources.
>>
>> E.g. drivers/media/platform/ti-vpe/cal.c uses
>> vb2_dma_contig_set_max_seg_size() and
>> vb2_dma_contig_clear_max_seg_size() to manage the dma_params, and
>> similar pattern is seen in other drivers too.
>>
>> After 9495b7e92f716ab2, vb2_dma_contig_set_max_seg_size() will not
>> allocate anything, but vb2_dma_contig_clear_max_seg_size() will still
>> kfree the dma_params.
>>
>> I'm not sure what's the proper fix here. A flag somewhere to indicate
>> that vb2_dma_contig_set_max_seg_size() did allocate, and thus
>> vb2_dma_contig_clear_max_seg_size() must free?
>>
>> Or drop the kzalloc and kfree totally, if dma_params is now supposed
>> to always be there?
> 
> Thanks for reporting this issue!
> 
> Once the mentioned commit has been merged, the code should assume that
> the platform devices does have a struct dma_params allocated, so the
> proper fix is to alloc dma_params only if the bus is not a platform bus:
> 
> if (!dev_is_platform(dev) && !dev->dma_parms) {
>       dev->dma_parms = kzalloc(sizeof(*dev->dma_parms), GFP_KERNEL);
> 
> same check for the free path.

There is also "amba: Initialize dma_parms for amba devices". And the commit message says PCI devices 
do this too.

Guessing this based on the device type doesn't sound like a good idea to me.

  Tomi

-- 
Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki