Re: [PATCH v3 6/9] dma-buf: Move dma-buf attachment to dynamic locking specification

Dmitry Osipenko
2022-08-24T15:04:00Z

On 8/24/22 17:08, Christian König wrote:
> Am 24.08.22 um 12:22 schrieb Dmitry Osipenko:
>> Move dma-buf attachment API functions to the dynamic locking
>> specification.
>> The strict locking convention prevents deadlock situations for dma-buf
>> importers and exporters.
>>
>> Previously, the "unlocked" versions of the attachment API functions
>> weren't taking the reservation lock and this patch makes them to take
>> the lock.
>
> Didn't we concluded that we need to keep the attach and detach callbacks
> without the lock and only move the map/unmap callbacks over?
>
> Otherwise it won't be possible for drivers to lock multiple buffers if
> they have to shuffle things around for a specific attachment.

We did conclude that. The attach/detach dma-buf ops are unlocked, but
the map_dma_buf/unmap_dma_buf must be invoked under lock and
dma_buf_dynamic_attach_unlocked() maps dma-buf if either importer or
exporter can't handle the dynamic mapping [1].

[1]
https://elixir.bootlin.com/linux/v6.0-rc2/source/drivers/dma-buf/dma-buf.c#L869

Hence I re-arranged the dma_resv_lock() in
dma_buf_dynamic_attach_unlocked() to move both pinning and mapping under
the held lock.

--
Best regards,
Dmitry