dma-buf, drm, ion: Propagate error code from dma_buf_start_cpu_access()

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
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1458331359-2634-1-git-send-email-chris@chris-wilson.co.uk

1 files changed, 3 insertions, 3 deletions

diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index 532108e..3fe90d4 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -94,7 +94,7 @@ struct dma_buf_ops {
 	void (*release)(struct dma_buf *);
 
 	int (*begin_cpu_access)(struct dma_buf *, enum dma_data_direction);
-	void (*end_cpu_access)(struct dma_buf *, enum dma_data_direction);
+	int (*end_cpu_access)(struct dma_buf *, enum dma_data_direction);
 	void *(*kmap_atomic)(struct dma_buf *, unsigned long);
 	void (*kunmap_atomic)(struct dma_buf *, unsigned long, void *);
 	void *(*kmap)(struct dma_buf *, unsigned long);
@@ -224,8 +224,8 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *, struct sg_table *,
 				enum dma_data_direction);
 int dma_buf_begin_cpu_access(struct dma_buf *dma_buf,
 			     enum dma_data_direction dir);
-void dma_buf_end_cpu_access(struct dma_buf *dma_buf,
-			    enum dma_data_direction dir);
+int dma_buf_end_cpu_access(struct dma_buf *dma_buf,
+			   enum dma_data_direction dir);
 void *dma_buf_kmap_atomic(struct dma_buf *, unsigned long);
 void dma_buf_kunmap_atomic(struct dma_buf *, unsigned long, void *);
 void *dma_buf_kmap(struct dma_buf *, unsigned long);