Re: [PATCH v4 2/6] dma-buf/heaps: Don't assert held reservation lock for dma-buf mmapping

T.J. Mercier
2023-06-21T19:24:30Z

On Wed, Jun 21, 2023 at 11:16 AM Dmitry Osipenko
<dmitry.osipenko@collabora.com> wrote:
>
> Hi,
>
> On 6/21/23 20:21, T.J. Mercier wrote:
> > On Mon, May 29, 2023 at 3:46 PM Dmitry Osipenko
> > <dmitry.osipenko@collabora.com> wrote:
> >>
> >> Don't assert held dma-buf reservation lock on memory mapping of exported
> >> buffer.
> >>
> >> We're going to change dma-buf mmap() locking policy such that exporters
> >> will have to handle the lock. The previous locking policy caused deadlock
> >> problem for DRM drivers in a case of self-imported dma-bufs once these
> >> drivers are moved to use reservation lock universally. The problem
> >> solved by moving the lock down to exporters. This patch prepares dma-buf
> >> heaps for the locking policy update.
> >>
> > Hi Dmitry,
> >
> > I see that in patch 6 of this series calls to
> > dma_resv_lock/dma_resv_unlock have been added to the
> > drm_gem_shmem_helper functions and some exporters. But I'm curious why
> > no dma_resv_lock/dma_resv_unlock calls were added to these two dma-buf
> > heap exporters for mmap?
>
> DMA-buf heaps are exporters, drm_gem_shmem_helper is importer. Locking
> rules are different for importers and exporters.
>
> DMA-heaps use own locking, they can be moved to resv lock in the future.
>
> DMA-heaps don't protect internal data in theirs mmap() implementations,
> nothing to protect there.
>
Thanks.