Re: [PATCH 08/51] drm/i915: Use drmm_add_final_kfree

[Jani Nikula <jani.nikula@linux.intel.com>]

On Mon, 23 Mar 2020, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> With this we can drop the final kfree from the release function.
>
> The mock device in the selftests needed it's pci_device split
> up from the drm_device. In the future we could simplify this again
> by allocating the pci_device as a managed allocation too.
>
> v2: I overlooked that i915_driver_destroy is also called in the
> unwind code of the error path. There we need a drm_dev_put.
> Similar for the mock object.
>
> Now the problem with that is that the drm_driver->release callbacks
> for both the real driver and the mock one assume everything has been
> set up. Hence going through that path for a partially set up driver
> will result in issues. Quickest fix is to disable the ->release() hook
> until the driver is fully initialized, and keep the onion unwinding.
> Long term would be cleanest to move everything over to drmm_ release
> actions, but that's a lot of work for a big driver like i915. Plus
> more core work needed first anyway.
>
> v3: Fix i915_drm pointer wrangling in mock_gem_device. Also switch
> over to start using drm_dev_put() to clean up even on the error path.
> Aside I think the current error path is leaking the allocation.
>
> v4: more fixes for intel-gfx-ci, some if it damage from v3 :-/
>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Matthew Auld <matthew.auld@intel.com>
> Cc: Andi Shyti <andi.shyti@intel.com>
> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Abdiel Janulgue <abdiel.janulgue@linux.intel.com>
> Cc: intel-gfx@lists.freedesktop.org

Okay, I didn't find any holes in this, and while I wish I had more
confidence I checked all the corner cases, this is

Reviewed-by: Jani Nikula <jani.nikula@intel.com>

A couple of notes below, don't have to do anything about them. (Maybe
better *not* to do anything about them, to move this forward. ;)

> ---
>  drivers/gpu/drm/i915/i915_drv.c               | 10 ++++++-
>  drivers/gpu/drm/i915/i915_drv.h               |  3 ++
>  .../gpu/drm/i915/selftests/mock_gem_device.c  | 30 ++++++++++++++-----
>  3 files changed, 35 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> index 4792051e9e2e..481313536b5a 100644
> --- a/drivers/gpu/drm/i915/i915_drv.c
> +++ b/drivers/gpu/drm/i915/i915_drv.c
> @@ -43,6 +43,7 @@
>  #include <drm/drm_atomic_helper.h>
>  #include <drm/drm_ioctl.h>
>  #include <drm/drm_irq.h>
> +#include <drm/drm_managed.h>
>  #include <drm/drm_probe_helper.h>
>  
>  #include "display/intel_acpi.h"
> @@ -890,6 +891,8 @@ i915_driver_create(struct pci_dev *pdev, const struct pci_device_id *ent)
>  		return ERR_PTR(err);
>  	}
>  
> +	drmm_add_final_kfree(&i915->drm, i915);
> +
>  	i915->drm.pdev = pdev;
>  	pci_set_drvdata(pdev, i915);
>  
> @@ -908,7 +911,6 @@ static void i915_driver_destroy(struct drm_i915_private *i915)
>  	struct pci_dev *pdev = i915->drm.pdev;
>  
>  	drm_dev_fini(&i915->drm);
> -	kfree(i915);
>  }
>  
>  /**
> @@ -992,6 +994,8 @@ int i915_driver_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
>  
>  	i915_welcome_messages(i915);
>  
> +	i915->do_release = true;
> +

This whole ->do_release thing is obviously a bummer. I did wonder if we
could set driver->release to NULL initially, and set it to the proper
thing here. It would make drm_dev_put() handle drm_dev_fini() internally
too.

Less obvious? I don't know.

>  	return 0;
>  
>  out_cleanup_irq:
> @@ -1012,6 +1016,7 @@ int i915_driver_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
>  out_fini:
>  	i915_probe_error(i915, "Device initialization failed (%d)\n", ret);
>  	i915_driver_destroy(i915);
> +	drm_dev_put(&i915->drm);

Also wondered about throwing i915_driver_destroy away, and inlining the
drm_dev_fini()...

>  	return ret;
>  }
>  
> @@ -1051,6 +1056,9 @@ static void i915_driver_release(struct drm_device *dev)
>  	struct drm_i915_private *dev_priv = to_i915(dev);
>  	struct intel_runtime_pm *rpm = &dev_priv->runtime_pm;
>  
> +	if (!dev_priv->do_release)

...or, calling drm_dev_fini() in this branch, avoiding the need to call
it elsewhere.

*shrug*

All of it can be done afterwards, if deemed useful.

> +		return;
> +
>  	disable_rpm_wakeref_asserts(rpm);
>  
>  	i915_gem_driver_release(dev_priv);
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index a7ea1d855359..7ae652723ed7 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -821,6 +821,9 @@ struct i915_selftest_stash {
>  struct drm_i915_private {
>  	struct drm_device drm;
>  
> +	/* FIXME: Device release actions should all be moved to drmm_ */
> +	bool do_release;
> +
>  	const struct intel_device_info __info; /* Use INTEL_INFO() to access. */
>  	struct intel_runtime_info __runtime; /* Use RUNTIME_INFO() to access. */
>  	struct intel_driver_caps caps;
> diff --git a/drivers/gpu/drm/i915/selftests/mock_gem_device.c b/drivers/gpu/drm/i915/selftests/mock_gem_device.c
> index 754d0eb6beaa..acf889e4b993 100644
> --- a/drivers/gpu/drm/i915/selftests/mock_gem_device.c
> +++ b/drivers/gpu/drm/i915/selftests/mock_gem_device.c
> @@ -25,6 +25,8 @@
>  #include <linux/pm_domain.h>
>  #include <linux/pm_runtime.h>
>  
> +#include <drm/drm_managed.h>
> +
>  #include "gt/intel_gt.h"
>  #include "gt/intel_gt_requests.h"
>  #include "gt/mock_engine.h"
> @@ -55,6 +57,9 @@ static void mock_device_release(struct drm_device *dev)
>  {
>  	struct drm_i915_private *i915 = to_i915(dev);
>  
> +	if (!i915->do_release)
> +		goto out;
> +
>  	mock_device_flush(i915);
>  	intel_gt_driver_remove(&i915->gt);
>  
> @@ -72,7 +77,9 @@ static void mock_device_release(struct drm_device *dev)
>  	drm_mode_config_cleanup(&i915->drm);
>  
>  	drm_dev_fini(&i915->drm);
> +out:
>  	put_device(&i915->drm.pdev->dev);
> +	i915->drm.pdev = NULL;
>  }
>  
>  static struct drm_driver mock_driver = {
> @@ -114,9 +121,14 @@ struct drm_i915_private *mock_gem_device(void)
>  	struct pci_dev *pdev;
>  	int err;
>  
> -	pdev = kzalloc(sizeof(*pdev) + sizeof(*i915), GFP_KERNEL);
> +	pdev = kzalloc(sizeof(*pdev), GFP_KERNEL);
>  	if (!pdev)
> -		goto err;
> +		return NULL;
> +	i915 = kzalloc(sizeof(*i915), GFP_KERNEL);
> +	if (!i915) {
> +		kfree(pdev);
> +		return NULL;
> +	}
>  
>  	device_initialize(&pdev->dev);
>  	pdev->class = PCI_BASE_CLASS_DISPLAY << 16;
> @@ -129,7 +141,6 @@ struct drm_i915_private *mock_gem_device(void)
>  	pdev->dev.archdata.iommu = (void *)-1;
>  #endif
>  
> -	i915 = (struct drm_i915_private *)(pdev + 1);
>  	pci_set_drvdata(pdev, i915);
>  
>  	dev_pm_domain_set(&pdev->dev, &pm_domain);
> @@ -141,9 +152,13 @@ struct drm_i915_private *mock_gem_device(void)
>  	err = drm_dev_init(&i915->drm, &mock_driver, &pdev->dev);
>  	if (err) {
>  		pr_err("Failed to initialise mock GEM device: err=%d\n", err);
> -		goto put_device;
> +		put_device(&pdev->dev);
> +		kfree(i915);
> +
> +		return NULL;
>  	}
>  	i915->drm.pdev = pdev;
> +	drmm_add_final_kfree(&i915->drm, i915);
>  
>  	intel_runtime_pm_init_early(&i915->runtime_pm);
>  
> @@ -188,6 +203,8 @@ struct drm_i915_private *mock_gem_device(void)
>  	__clear_bit(I915_WEDGED, &i915->gt.reset.flags);
>  	intel_engines_driver_register(i915);
>  
> +	i915->do_release = true;
> +
>  	return i915;
>  
>  err_context:
> @@ -199,8 +216,7 @@ struct drm_i915_private *mock_gem_device(void)
>  	intel_memory_regions_driver_release(i915);
>  	drm_mode_config_cleanup(&i915->drm);
>  	drm_dev_fini(&i915->drm);
> -put_device:
> -	put_device(&pdev->dev);
> -err:
> +	drm_dev_put(&i915->drm);
> +
>  	return NULL;
>  }

-- 
Jani Nikula, Intel Open Source Graphics Center
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