Re: [PATCH] drm/fb-helper: Remove drm_fb_helper_unprepare() from drm_fb_helper_fini()

Hi

Am 16.02.23 um 21:11 schrieb Daniel Vetter:

On Thu, Feb 16, 2023 at 03:06:20PM +0100, Thomas Zimmermann wrote:

quoted

Move drm_fb_helper_unprepare() from drm_fb_helper_fini() into the
calling fbdev implementation. Avoids a possible stale mutex with
generic fbdev code.

As indicated by its name, drm_fb_helper_prepare() prepares struct
drm_fb_helper before setting up the fbdev support with a call to
drm_fb_helper_init(). In legacy fbdev emulation, this happens next
to each other. If successful, drm_fb_helper_fini() later tear down
the fbdev device and also unprepare via drm_fb_helper_unprepare().

Generic fbdev emulation prepares struct drm_fb_helper immediately
after allocating the instance. It only calls drm_fb_helper_init()
as part of processing a hotplug event. If the hotplug-handling fails,
it runs drm_fb_helper_fini(). This unprepares the fb-helper instance
and the next hotplug event runs on stale data.

Solve this by moving drm_fb_helper_unprepare() from drm_fb_helper_fini()
into the fbdev implementations. Call it right before freeing the
fb-helper instance.

Fixes: 4825797c36da ("drm/fb-helper: Introduce drm_fb_helper_unprepare()")
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Javier Martinez Canillas <javierm@redhat.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: David Airlie <airlied@gmail.com>
Cc: Daniel Vetter <redacted>
Cc: dri-devel@lists.freedesktop.org

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>

This reminds me of an old patch I just recently stumbled over again:

https://lore.kernel.org/dri-devel/Y3St2VHJ7jEmcNFw@phenom.ffwll.local/ (local)

Should I resurrect that one maybe and send it out? I think that also ties
a bit into your story here.

I don't think it will be necessary. I began to convert the existing 
fbdev emulation to make use of drm_client, which should resove a number 
of problems. I expect to post this after the various trees have merged 
the recent changes to fbdev helpers.

Best regards
Thomas

quoted

---
  drivers/gpu/drm/armada/armada_fbdev.c      | 3 +++
  drivers/gpu/drm/drm_fb_helper.c            | 2 --
  drivers/gpu/drm/drm_fbdev_generic.c        | 2 ++
  drivers/gpu/drm/exynos/exynos_drm_fbdev.c  | 3 ++-
  drivers/gpu/drm/gma500/framebuffer.c       | 2 ++
  drivers/gpu/drm/i915/display/intel_fbdev.c | 1 +
  drivers/gpu/drm/msm/msm_fbdev.c            | 2 ++
  drivers/gpu/drm/omapdrm/omap_fbdev.c       | 2 ++
  drivers/gpu/drm/radeon/radeon_fb.c         | 2 ++
  drivers/gpu/drm/tegra/fb.c                 | 1 +
  10 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/armada/armada_fbdev.c b/drivers/gpu/drm/armada/armada_fbdev.c
index 07e410c62b7a..0e44f53e9fa4 100644
--- a/drivers/gpu/drm/armada/armada_fbdev.c
+++ b/drivers/gpu/drm/armada/armada_fbdev.c

@@ -147,6 +147,7 @@ int armada_fbdev_init(struct drm_device *dev)
   err_fb_setup:
  	drm_fb_helper_fini(fbh);
   err_fb_helper:
+	drm_fb_helper_unprepare(fbh);
  	priv->fbdev = NULL;
  	return ret;
  }

@@ -164,6 +165,8 @@ void armada_fbdev_fini(struct drm_device *dev)
  		if (fbh->fb)
  			fbh->fb->funcs->destroy(fbh->fb);
  
+		drm_fb_helper_unprepare(fbh);
+
  		priv->fbdev = NULL;
  	}
  }

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index 28c428e9c530..a39998047f8a 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c

@@ -590,8 +590,6 @@ void drm_fb_helper_fini(struct drm_fb_helper *fb_helper)

I think it would be good to update the kerneldoc of _init() and _fini()
here to mention each another like we usually do with these pairs. Same
with prepare/unprepare() although the latter rerfences _prepare() already.

quoted

  	}
  	mutex_unlock(&kernel_fb_helper_lock);
  
-	drm_fb_helper_unprepare(fb_helper);
-
  	if (!fb_helper->client.funcs)
  		drm_client_release(&fb_helper->client);
  }

diff --git a/drivers/gpu/drm/drm_fbdev_generic.c b/drivers/gpu/drm/drm_fbdev_generic.c
index 365f80717fa1..4d6325e91565 100644
--- a/drivers/gpu/drm/drm_fbdev_generic.c
+++ b/drivers/gpu/drm/drm_fbdev_generic.c

@@ -65,6 +65,8 @@ static void drm_fbdev_fb_destroy(struct fb_info *info)
  
  	drm_client_framebuffer_delete(fb_helper->buffer);
  	drm_client_release(&fb_helper->client);
+
+	drm_fb_helper_unprepare(fb_helper);
  	kfree(fb_helper);
  }
  

diff --git a/drivers/gpu/drm/exynos/exynos_drm_fbdev.c b/drivers/gpu/drm/exynos/exynos_drm_fbdev.c
index b89e33af8da8..4929ffe5a09a 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_fbdev.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_fbdev.c

@@ -183,8 +183,8 @@ int exynos_drm_fbdev_init(struct drm_device *dev)
  
  err_setup:
  	drm_fb_helper_fini(helper);
-
  err_init:
+	drm_fb_helper_unprepare(helper);
  	private->fb_helper = NULL;
  	kfree(fbdev);
  

@@ -219,6 +219,7 @@ void exynos_drm_fbdev_fini(struct drm_device *dev)
  	fbdev = to_exynos_fbdev(private->fb_helper);
  
  	exynos_drm_fbdev_destroy(dev, private->fb_helper);
+	drm_fb_helper_unprepare(private->fb_helper);
  	kfree(fbdev);
  	private->fb_helper = NULL;
  }

diff --git a/drivers/gpu/drm/gma500/framebuffer.c b/drivers/gpu/drm/gma500/framebuffer.c
index 1f04c07ee180..f471e0cb7298 100644
--- a/drivers/gpu/drm/gma500/framebuffer.c
+++ b/drivers/gpu/drm/gma500/framebuffer.c

@@ -427,6 +427,7 @@ int psb_fbdev_init(struct drm_device *dev)
  fini:
  	drm_fb_helper_fini(fb_helper);
  free:
+	drm_fb_helper_unprepare(fb_helper);
  	kfree(fb_helper);
  	return ret;
  }

@@ -439,6 +440,7 @@ static void psb_fbdev_fini(struct drm_device *dev)
  		return;
  
  	psb_fbdev_destroy(dev, dev_priv->fb_helper);
+	drm_fb_helper_unprepare(dev_priv->fb_helper);
  	kfree(dev_priv->fb_helper);
  	dev_priv->fb_helper = NULL;
  }

diff --git a/drivers/gpu/drm/i915/display/intel_fbdev.c b/drivers/gpu/drm/i915/display/intel_fbdev.c
index 6113d7627d45..98029059f701 100644
--- a/drivers/gpu/drm/i915/display/intel_fbdev.c
+++ b/drivers/gpu/drm/i915/display/intel_fbdev.c

@@ -352,6 +352,7 @@ static void intel_fbdev_destroy(struct intel_fbdev *ifbdev)
  	if (ifbdev->fb)
  		drm_framebuffer_remove(&ifbdev->fb->base);
  
+	drm_fb_helper_unprepare(&ifbdev->helper);
  	kfree(ifbdev);
  }
  

diff --git a/drivers/gpu/drm/msm/msm_fbdev.c b/drivers/gpu/drm/msm/msm_fbdev.c
index 915b213f3a5c..c804e5ba682a 100644
--- a/drivers/gpu/drm/msm/msm_fbdev.c
+++ b/drivers/gpu/drm/msm/msm_fbdev.c

@@ -170,6 +170,7 @@ struct drm_fb_helper *msm_fbdev_init(struct drm_device *dev)
  fini:
  	drm_fb_helper_fini(helper);
  fail:
+	drm_fb_helper_unprepare(helper);
  	kfree(fbdev);
  	return NULL;
  }

@@ -196,6 +197,7 @@ void msm_fbdev_free(struct drm_device *dev)
  		drm_framebuffer_remove(fbdev->fb);
  	}
  
+	drm_fb_helper_unprepare(helper);
  	kfree(fbdev);
  
  	priv->fbdev = NULL;

diff --git a/drivers/gpu/drm/omapdrm/omap_fbdev.c b/drivers/gpu/drm/omapdrm/omap_fbdev.c
index fc5f52d567c6..84429728347f 100644
--- a/drivers/gpu/drm/omapdrm/omap_fbdev.c
+++ b/drivers/gpu/drm/omapdrm/omap_fbdev.c

@@ -256,6 +256,7 @@ void omap_fbdev_init(struct drm_device *dev)
  fini:
  	drm_fb_helper_fini(helper);
  fail:
+	drm_fb_helper_unprepare(helper);
  	kfree(fbdev);
  
  	dev_warn(dev->dev, "omap_fbdev_init failed\n");

@@ -286,6 +287,7 @@ void omap_fbdev_fini(struct drm_device *dev)
  	if (fbdev->fb)
  		drm_framebuffer_remove(fbdev->fb);
  
+	drm_fb_helper_unprepare(helper);
  	kfree(fbdev);
  
  	priv->fbdev = NULL;

diff --git a/drivers/gpu/drm/radeon/radeon_fb.c b/drivers/gpu/drm/radeon/radeon_fb.c
index 6e5eed0e157c..c4807f0c43bc 100644
--- a/drivers/gpu/drm/radeon/radeon_fb.c
+++ b/drivers/gpu/drm/radeon/radeon_fb.c

@@ -367,6 +367,7 @@ int radeon_fbdev_init(struct radeon_device *rdev)
  fini:
  	drm_fb_helper_fini(&rfbdev->helper);
  free:
+	drm_fb_helper_unprepare(&rfbdev->helper);
  	kfree(rfbdev);
  	return ret;
  }

@@ -377,6 +378,7 @@ void radeon_fbdev_fini(struct radeon_device *rdev)
  		return;
  
  	radeon_fbdev_destroy(rdev->ddev, rdev->mode_info.rfbdev);
+	drm_fb_helper_unprepare(&rdev->mode_info.rfbdev->helper);
  	kfree(rdev->mode_info.rfbdev);
  	rdev->mode_info.rfbdev = NULL;
  }

diff --git a/drivers/gpu/drm/tegra/fb.c b/drivers/gpu/drm/tegra/fb.c
index 153c39c32c71..bfebe2786d61 100644
--- a/drivers/gpu/drm/tegra/fb.c
+++ b/drivers/gpu/drm/tegra/fb.c

@@ -315,6 +315,7 @@ static struct tegra_fbdev *tegra_fbdev_create(struct drm_device *drm)
  
  static void tegra_fbdev_free(struct tegra_fbdev *fbdev)
  {
+	drm_fb_helper_unprepare(&fbdev->base);

Ok this one tegra change was a bit tricky, drivers really should just use
drmm_/devm_ for everything :-)

With the kerneldoc augmented:

Reviewed-by: Daniel Vetter <redacted>

quoted

  	kfree(fbdev);
  }
  
-- 
2.39.1

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev