linux-kernel - [PATCH] drm/virtio: exbuf->fence_fd unmodified on interrupted wait

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Date:   Thu, 26 Jan 2023 14:58:15 -0800
From:   Ryan Neph <ryanneph@...omium.org>
To:     David Airlie <airlied@...hat.com>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Gurchetan Singh <gurchetansingh@...omium.org>,
        Chia-I Wu <olvaffe@...il.com>, dri-devel@...ts.freedesktop.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Cc:     Yiwei Zhang <zzyiwei@...omium.org>,
        Rob Clark <robdclark@...omium.org>,
        Ryan Neph <ryanneph@...omium.org>,
        Emil Velikov <emil.velikov@...labora.com>,
        Gustavo Padovan <gustavo.padovan@...labora.com>,
        Robert Foss <robert.foss@...labora.com>
Subject: [PATCH] drm/virtio: exbuf->fence_fd unmodified on interrupted wait

An interrupted dma_fence_wait() becomes an -ERESTARTSYS returned
to userspace ioctl(DRM_IOCTL_VIRTGPU_EXECBUFFER) calls, prompting to
retry the ioctl(), but the passed exbuf->fence_fd has been reset to -1,
making the retry attempt fail at sync_file_get_fence().

The uapi for DRM_IOCTL_VIRTGPU_EXECBUFFER is changed to retain the
passed value for exbuf->fence_fd when returning ERESTARTSYS or EINTR.

Fixes: 2cd7b6f08bc4 ("drm/virtio: add in/out fence support for explicit synchronization")
Signed-off-by: Ryan Neph <ryanneph@...omium.org>
---

 drivers/gpu/drm/virtio/virtgpu_ioctl.c | 9 ++++++---
 include/uapi/drm/virtgpu_drm.h         | 3 +++
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/virtio/virtgpu_ioctl.c b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
index 9f4a90493aea..ffce4e2a409a 100644
--- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c
+++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
@@ -132,6 +132,8 @@ static int virtio_gpu_execbuffer_ioctl(struct drm_device *dev, void *data,
 	uint64_t fence_ctx;
 	uint32_t ring_idx;
 
+	exbuf->fence_fd = -1;
+
 	fence_ctx = vgdev->fence_drv.context;
 	ring_idx = 0;
 
@@ -152,8 +154,6 @@ static int virtio_gpu_execbuffer_ioctl(struct drm_device *dev, void *data,
 		ring_idx = exbuf->ring_idx;
 	}
 
-	exbuf->fence_fd = -1;
-
 	virtio_gpu_create_context(dev, file);
 	if (exbuf->flags & VIRTGPU_EXECBUF_FENCE_FD_IN) {
 		struct dma_fence *in_fence;
@@ -173,7 +173,7 @@ static int virtio_gpu_execbuffer_ioctl(struct drm_device *dev, void *data,
 
 		dma_fence_put(in_fence);
 		if (ret)
-			return ret;
+			goto out_err;
 	}
 
 	if (exbuf->flags & VIRTGPU_EXECBUF_FENCE_FD_OUT) {
@@ -259,6 +259,9 @@ static int virtio_gpu_execbuffer_ioctl(struct drm_device *dev, void *data,
 
 	if (out_fence_fd >= 0)
 		put_unused_fd(out_fence_fd);
+out_err:
+	if (ret == -EINTR || ret == -ERESTARTSYS)
+		exbuf->fence_fd = in_fence_fd;
 
 	return ret;
 }
diff --git a/include/uapi/drm/virtgpu_drm.h b/include/uapi/drm/virtgpu_drm.h
index 0512fde5e697..ac8d1eed12ab 100644
--- a/include/uapi/drm/virtgpu_drm.h
+++ b/include/uapi/drm/virtgpu_drm.h
@@ -64,6 +64,9 @@ struct drm_virtgpu_map {
 	__u32 pad;
 };
 
+/* For ioctl() returning ERESTARTSYS or EINTR, fence_fd is unmodified.
+ * For all other errors it is set to -1.
+ */
 struct drm_virtgpu_execbuffer {
 	__u32 flags;
 	__u32 size;
-- 
2.39.1.456.gfc5497dd1b-goog