[Intel-gfx] [PATCH] dma-buf, drm, ion: Propagate error code from dma_buf_start_cpu_access()

[Tiago Vignatti]

On 03/18/2016 05:02 PM, Chris Wilson wrote:
> Drivers, especially i915.ko, can fail during the initial migration of a
> dma-buf for CPU access. However, the error code from the driver was not
> being propagated back to ioctl and so userspace was blissfully ignorant
> of the failure. Rendering corruption ensues.
>
> Whilst fixing the ioctl to return the error code from
> dma_buf_start_cpu_access(), also do the same for
> dma_buf_end_cpu_access().  For most drivers, dma_buf_end_cpu_access()
> cannot fail. i915.ko however, as most drivers would, wants to avoid being
> uninterruptible (as would be required to guarrantee no failure when
> flushing the buffer to the device). As userspace already has to handle
> errors from the SYNC_IOCTL, take advantage of this to be able to restart
> the syscall across signals.
>
> This fixes a coherency issue for i915.ko as well as reducing the
> uninterruptible hold upon its BKL, the struct_mutex.
>
> Fixes commit c11e391da2a8fe973c3c2398452000bed505851e
> Author: Daniel Vetter <daniel.vetter at ffwll.ch>
> Date:   Thu Feb 11 20:04:51 2016 -0200
>
>      dma-buf: Add ioctls to allow userspace to flush
>
> Testcase: igt/gem_concurrent_blit/*dmabuf*interruptible
> Testcase: igt/prime_mmap_coherency/ioctl-errors
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Tiago Vignatti <tiago.vignatti at intel.com>
> Cc: Stéphane Marchesin <marcheu at chromium.org>
> Cc: David Herrmann <dh.herrmann at gmail.com>
> Cc: Sumit Semwal <sumit.semwal at linaro.org>
> Cc: Daniel Vetter <daniel.vetter at intel.com>
> CC: linux-media at vger.kernel.org
> Cc: dri-devel at lists.freedesktop.org
> Cc: linaro-mm-sig at lists.linaro.org
> Cc: intel-gfx at lists.freedesktop.org
> Cc: devel at driverdev.osuosl.org

Reviewed-by: Tiago Vignatti <tiago.vignatti at intel.com>

Best regards,

Tiago