Re: [PATCH] drm/radeon: add an exclusive lock for GPU reset

[Christian König <deathsimple@xxxxxxxxxxx>]

On 02.07.2012 17:39, j.glisse@xxxxxxxxx wrote:
> From: Jerome Glisse <jglisse@xxxxxxxxxx>
>
> GPU reset need to be exclusive, one happening at a time. For this
> add a rw semaphore so that any path that trigger GPU activities
> have to take the semaphore as a reader thus allowing concurency.
>
> The GPU reset path take the semaphore as a writer ensuring that
> no concurrent reset take place.
>
> Signed-off-by: Jerome Glisse <jglisse@xxxxxxxxxx>
NAK, that isn't as bad as the cs mutex was but still to complicated. 
It's just too far up in the call stack, e.g. it tries to catch ioctl 
operations, instead of catching the underlying hardware operation which 
is caused by the ioctl/ttm/etc...

Why not just take the ring look as I suggested?

Christian.
> ---
>   drivers/gpu/drm/radeon/radeon.h        |    1 +
>   drivers/gpu/drm/radeon/radeon_cs.c     |    5 +++++
>   drivers/gpu/drm/radeon/radeon_device.c |    2 ++
>   drivers/gpu/drm/radeon/radeon_gem.c    |    7 +++++++
>   4 files changed, 15 insertions(+)
>
> diff --git a/drivers/gpu/drm/radeon/radeon.h b/drivers/gpu/drm/radeon/radeon.h
> index 77b4519b..29d6986 100644
> --- a/drivers/gpu/drm/radeon/radeon.h
> +++ b/drivers/gpu/drm/radeon/radeon.h
> @@ -1446,6 +1446,7 @@ struct radeon_device {
>   	struct device			*dev;
>   	struct drm_device		*ddev;
>   	struct pci_dev			*pdev;
> +	struct rw_semaphore		exclusive_lock;
>   	/* ASIC */
>   	union radeon_asic_config	config;
>   	enum radeon_family		family;
> diff --git a/drivers/gpu/drm/radeon/radeon_cs.c b/drivers/gpu/drm/radeon/radeon_cs.c
> index f1b7527..7ee6491 100644
> --- a/drivers/gpu/drm/radeon/radeon_cs.c
> +++ b/drivers/gpu/drm/radeon/radeon_cs.c
> @@ -499,7 +499,9 @@ int radeon_cs_ioctl(struct drm_device *dev, void *data, struct drm_file *filp)
>   	struct radeon_cs_parser parser;
>   	int r;
>   
> +	down_read(&rdev->exclusive_lock);
>   	if (!rdev->accel_working) {
> +		up_read(&rdev->exclusive_lock);
>   		return -EBUSY;
>   	}
>   	/* initialize parser */
> @@ -512,6 +514,7 @@ int radeon_cs_ioctl(struct drm_device *dev, void *data, struct drm_file *filp)
>   	if (r) {
>   		DRM_ERROR("Failed to initialize parser !\n");
>   		radeon_cs_parser_fini(&parser, r);
> +		up_read(&rdev->exclusive_lock);
>   		r = radeon_cs_handle_lockup(rdev, r);
>   		return r;
>   	}
> @@ -520,6 +523,7 @@ int radeon_cs_ioctl(struct drm_device *dev, void *data, struct drm_file *filp)
>   		if (r != -ERESTARTSYS)
>   			DRM_ERROR("Failed to parse relocation %d!\n", r);
>   		radeon_cs_parser_fini(&parser, r);
> +		up_read(&rdev->exclusive_lock);
>   		r = radeon_cs_handle_lockup(rdev, r);
>   		return r;
>   	}
> @@ -533,6 +537,7 @@ int radeon_cs_ioctl(struct drm_device *dev, void *data, struct drm_file *filp)
>   	}
>   out:
>   	radeon_cs_parser_fini(&parser, r);
> +	up_read(&rdev->exclusive_lock);
>   	r = radeon_cs_handle_lockup(rdev, r);
>   	return r;
>   }
> diff --git a/drivers/gpu/drm/radeon/radeon_device.c b/drivers/gpu/drm/radeon/radeon_device.c
> index f654ba8..c8fdb40 100644
> --- a/drivers/gpu/drm/radeon/radeon_device.c
> +++ b/drivers/gpu/drm/radeon/radeon_device.c
> @@ -988,6 +988,7 @@ int radeon_gpu_reset(struct radeon_device *rdev)
>   	int r;
>   	int resched;
>   
> +	down_write(&rdev->exclusive_lock);
>   	radeon_save_bios_scratch_regs(rdev);
>   	/* block TTM */
>   	resched = ttm_bo_lock_delayed_workqueue(&rdev->mman.bdev);
> @@ -1007,6 +1008,7 @@ int radeon_gpu_reset(struct radeon_device *rdev)
>   		dev_info(rdev->dev, "GPU reset failed\n");
>   	}
>   
> +	up_write(&rdev->exclusive_lock);
>   	return r;
>   }
>   
> diff --git a/drivers/gpu/drm/radeon/radeon_gem.c b/drivers/gpu/drm/radeon/radeon_gem.c
> index d9b0809..f99db63 100644
> --- a/drivers/gpu/drm/radeon/radeon_gem.c
> +++ b/drivers/gpu/drm/radeon/radeon_gem.c
> @@ -215,12 +215,14 @@ int radeon_gem_create_ioctl(struct drm_device *dev, void *data,
>   	uint32_t handle;
>   	int r;
>   
> +	down_read(&rdev->exclusive_lock);
>   	/* create a gem object to contain this object in */
>   	args->size = roundup(args->size, PAGE_SIZE);
>   	r = radeon_gem_object_create(rdev, args->size, args->alignment,
>   					args->initial_domain, false,
>   					false, &gobj);
>   	if (r) {
> +		up_read(&rdev->exclusive_lock);
>   		r = radeon_gem_handle_lockup(rdev, r);
>   		return r;
>   	}
> @@ -228,10 +230,12 @@ int radeon_gem_create_ioctl(struct drm_device *dev, void *data,
>   	/* drop reference from allocate - handle holds it now */
>   	drm_gem_object_unreference_unlocked(gobj);
>   	if (r) {
> +		up_read(&rdev->exclusive_lock);
>   		r = radeon_gem_handle_lockup(rdev, r);
>   		return r;
>   	}
>   	args->handle = handle;
> +	up_read(&rdev->exclusive_lock);
>   	return 0;
>   }
>   
> @@ -240,6 +244,7 @@ int radeon_gem_set_domain_ioctl(struct drm_device *dev, void *data,
>   {
>   	/* transition the BO to a domain -
>   	 * just validate the BO into a certain domain */
> +	struct radeon_device *rdev = dev->dev_private;
>   	struct drm_radeon_gem_set_domain *args = data;
>   	struct drm_gem_object *gobj;
>   	struct radeon_bo *robj;
> @@ -255,9 +260,11 @@ int radeon_gem_set_domain_ioctl(struct drm_device *dev, void *data,
>   	}
>   	robj = gem_to_radeon_bo(gobj);
>   
> +	down_read(&rdev->exclusive_lock);
>   	r = radeon_gem_set_domain(gobj, args->read_domains, args->write_domain);
>   
>   	drm_gem_object_unreference_unlocked(gobj);
> +	up_read(&rdev->exclusive_lock);
>   	r = radeon_gem_handle_lockup(robj->rdev, r);
>   	return r;
>   }


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