Re: [PATCH 02/10] dmaengine: virt-dma: Support for race free transfer termination

[Linus Walleij]

On Tue, Nov 14, 2017 at 3:32 PM, Peter Ujfalusi <peter.ujfalusi@xxxxxx> wrote:

> Even with the introduced vchan_synchronize() we can face race when
> terminating a cyclic transfer.
>
> If the terminate_all is called after the interrupt handler called
> vchan_cyclic_callback(), but before the vchan_complete tasklet is called:
> vc->cyclic is set to the cyclic descriptor, but the descriptor itself was
> freed up in the driver's terminate_all() callback.
> When the vhan_complete() is executed it will try to fetch the vc->cyclic
> vdesc, but the pointer is pointing now to uninitialized memory leading to
> (hard to reproduce) kernel crash.
>
> In order to fix this, drivers should:
> - call vchan_terminate_vdesc() from their terminate_all callback instead
> calling their free_desc function to free up the descriptor.
> - implement device_synchronize callback and call vchan_synchronize().
>
> This way we can make sure that the descriptor is only going to be freed up
> after the vchan_callback was executed in a safe manner.
>
> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@xxxxxx>

Reviewed-by: Linus Walleij <linus.walleij@xxxxxxxxxx>

Yours,
Linus Walleij