[v1,5/7] Revert "drm: Assert held reservation lock for dma-buf mmapping"

Message ID 20230402164826.752842-6-dmitry.osipenko@collabora.com
State New
Headers
Series Move dma-buf mmap() reservation locking down to exporters |

Commit Message

Dmitry Osipenko April 2, 2023, 4:48 p.m. UTC
  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, it's solved
by moving the lock down to exporters.

Fixes: 39ce25291871 ("drm: Assert held reservation lock for dma-buf mmapping")
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
---
 drivers/gpu/drm/drm_prime.c                | 2 --
 drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 2 --
 drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c  | 2 --
 drivers/gpu/drm/tegra/gem.c                | 2 --
 4 files changed, 8 deletions(-)
  

Comments

Christian König April 3, 2023, 3:17 p.m. UTC | #1
Am 02.04.23 um 18:48 schrieb Dmitry Osipenko:
> 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, it's solved
> by moving the lock down to exporters.

I only checked the TTM code path and think that at least that one should 
work fine.

> Fixes: 39ce25291871 ("drm: Assert held reservation lock for dma-buf mmapping")

This here is not really a "fix" for the previous patch. We just found 
that we didn't like the behavior and so reverted the original patch.

A "Reverts..." comment in the commit message would be more appropriate I 
think.

> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>

Acked-by: Christian König <christian.koenig@amd.com>

Regards,
Christian.

> ---
>   drivers/gpu/drm/drm_prime.c                | 2 --
>   drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 2 --
>   drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c  | 2 --
>   drivers/gpu/drm/tegra/gem.c                | 2 --
>   4 files changed, 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> index 149cd4ff6a3b..cea85e84666f 100644
> --- a/drivers/gpu/drm/drm_prime.c
> +++ b/drivers/gpu/drm/drm_prime.c
> @@ -781,8 +781,6 @@ int drm_gem_dmabuf_mmap(struct dma_buf *dma_buf, struct vm_area_struct *vma)
>   	struct drm_gem_object *obj = dma_buf->priv;
>   	struct drm_device *dev = obj->dev;
>   
> -	dma_resv_assert_held(dma_buf->resv);
> -
>   	if (!dev->driver->gem_prime_mmap)
>   		return -ENOSYS;
>   
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> index fd556a076d05..1df74f7aa3dc 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> @@ -97,8 +97,6 @@ static int i915_gem_dmabuf_mmap(struct dma_buf *dma_buf, struct vm_area_struct *
>   	struct drm_i915_private *i915 = to_i915(obj->base.dev);
>   	int ret;
>   
> -	dma_resv_assert_held(dma_buf->resv);
> -
>   	if (obj->base.size < vma->vm_end - vma->vm_start)
>   		return -EINVAL;
>   
> diff --git a/drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c b/drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c
> index 3abc47521b2c..8e194dbc9506 100644
> --- a/drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c
> +++ b/drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c
> @@ -66,8 +66,6 @@ static int omap_gem_dmabuf_mmap(struct dma_buf *buffer,
>   	struct drm_gem_object *obj = buffer->priv;
>   	int ret = 0;
>   
> -	dma_resv_assert_held(buffer->resv);
> -
>   	ret = drm_gem_mmap_obj(obj, omap_gem_mmap_size(obj), vma);
>   	if (ret < 0)
>   		return ret;
> diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
> index bce991a2ccc0..871ef5d26523 100644
> --- a/drivers/gpu/drm/tegra/gem.c
> +++ b/drivers/gpu/drm/tegra/gem.c
> @@ -693,8 +693,6 @@ static int tegra_gem_prime_mmap(struct dma_buf *buf, struct vm_area_struct *vma)
>   	struct drm_gem_object *gem = buf->priv;
>   	int err;
>   
> -	dma_resv_assert_held(buf->resv);
> -
>   	err = drm_gem_mmap_obj(gem, gem->size, vma);
>   	if (err < 0)
>   		return err;
  
Dmitry Osipenko April 5, 2023, 12:33 a.m. UTC | #2
On 4/3/23 18:17, Christian König wrote:
> Am 02.04.23 um 18:48 schrieb Dmitry Osipenko:
>> 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, it's solved
>> by moving the lock down to exporters.
> 
> I only checked the TTM code path and think that at least that one should
> work fine.
> 
>> Fixes: 39ce25291871 ("drm: Assert held reservation lock for dma-buf
>> mmapping")
> 
> This here is not really a "fix" for the previous patch. We just found
> that we didn't like the behavior and so reverted the original patch.
> 
> A "Reverts..." comment in the commit message would be more appropriate I
> think.

Ack, will drop the fixes tag in v2. Thank you and Emil for the review.
  

Patch

diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 149cd4ff6a3b..cea85e84666f 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -781,8 +781,6 @@  int drm_gem_dmabuf_mmap(struct dma_buf *dma_buf, struct vm_area_struct *vma)
 	struct drm_gem_object *obj = dma_buf->priv;
 	struct drm_device *dev = obj->dev;
 
-	dma_resv_assert_held(dma_buf->resv);
-
 	if (!dev->driver->gem_prime_mmap)
 		return -ENOSYS;
 
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
index fd556a076d05..1df74f7aa3dc 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
@@ -97,8 +97,6 @@  static int i915_gem_dmabuf_mmap(struct dma_buf *dma_buf, struct vm_area_struct *
 	struct drm_i915_private *i915 = to_i915(obj->base.dev);
 	int ret;
 
-	dma_resv_assert_held(dma_buf->resv);
-
 	if (obj->base.size < vma->vm_end - vma->vm_start)
 		return -EINVAL;
 
diff --git a/drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c b/drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c
index 3abc47521b2c..8e194dbc9506 100644
--- a/drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c
+++ b/drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c
@@ -66,8 +66,6 @@  static int omap_gem_dmabuf_mmap(struct dma_buf *buffer,
 	struct drm_gem_object *obj = buffer->priv;
 	int ret = 0;
 
-	dma_resv_assert_held(buffer->resv);
-
 	ret = drm_gem_mmap_obj(obj, omap_gem_mmap_size(obj), vma);
 	if (ret < 0)
 		return ret;
diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
index bce991a2ccc0..871ef5d26523 100644
--- a/drivers/gpu/drm/tegra/gem.c
+++ b/drivers/gpu/drm/tegra/gem.c
@@ -693,8 +693,6 @@  static int tegra_gem_prime_mmap(struct dma_buf *buf, struct vm_area_struct *vma)
 	struct drm_gem_object *gem = buf->priv;
 	int err;
 
-	dma_resv_assert_held(buf->resv);
-
 	err = drm_gem_mmap_obj(gem, gem->size, vma);
 	if (err < 0)
 		return err;