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Subject: Re: [PATCH] dma-buf,drm,ion: Propagate error code from
 dma_buf_start_cpu_access()
To: Chris Wilson <chris@chris-wilson.co.uk>,
	intel-gfx@lists.freedesktop.org
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From: Tiago Vignatti <tiago.vignatti@intel.com>
Message-ID: <56EFF366.3080908@intel.com>
Date: Mon, 21 Mar 2016 10:13:10 -0300
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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@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@chris-wilson.co.uk>
> Cc: Tiago Vignatti <tiago.vignatti@intel.com>
> Cc: Stéphane Marchesin <marcheu@chromium.org>
> Cc: David Herrmann <dh.herrmann@gmail.com>
> Cc: Sumit Semwal <sumit.semwal@linaro.org>
> Cc: Daniel Vetter <daniel.vetter@intel.com>
> CC: linux-media@vger.kernel.org
> Cc: dri-devel@lists.freedesktop.org
> Cc: linaro-mm-sig@lists.linaro.org
> Cc: intel-gfx@lists.freedesktop.org
> Cc: devel@driverdev.osuosl.org

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

Best regards,

Tiago