On Thu, Feb 16, 2023 at 03:06:20PM +0100, Thomas Zimmermann wrote:
> 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@xxxxxxx>
> Cc: Javier Martinez Canillas <javierm@xxxxxxxxxx>
> Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> Cc: Maxime Ripard <mripard@xxxxxxxxxx>
> Cc: David Airlie <airlied@xxxxxxxxx>
> Cc: Daniel Vetter <daniel@xxxxxxxx>
> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
>
> Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
This reminds me of an old patch I just recently stumbled over again:
https://lore.kernel.org/dri-devel/Y3St2VHJ7jEmcNFw@phenom.ffwll.local/
Should I resurrect that one maybe and send it out? I think that also ties
a bit into your story here.
> ---
> 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.
> }
> 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 <daniel.vetter@xxxxxxxx>
> kfree(fbdev);
> }
>
> --
> 2.39.1
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
