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

[Tomi Valkeinen]

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) {
>   ÂÂÂ 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

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