linux-kernel - Re: [PATCH v5 3/7] fbdev: Restart conflicting fb removal loop when unregistering devices

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Date:   Fri, 13 May 2022 14:28:23 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Helge Deller <deller@....de>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v5 3/7] fbdev: Restart conflicting fb removal loop when
 unregistering devices

On 5/11/22 13:30, Javier Martinez Canillas wrote:
> Drivers that want to remove registered conflicting framebuffers prior to
> register their own framebuffer, calls remove_conflicting_framebuffers().
> 
> This function takes the registration_lock mutex, to prevent a races when
> drivers register framebuffer devices. But if a conflicting framebuffer
> device is found, the underlaying platform device is unregistered and this
> will lead to the platform driver .remove callback to be called, which in
> turn will call to the unregister_framebuffer() that takes the same lock.
> 
> To prevent this, a struct fb_info.forced_out field was used as indication
> to unregister_framebuffer() whether the mutex has to be grabbed or not.
> 
> A cleaner solution is to drop the lock before platform_device_unregister()
> so unregister_framebuffer() can take it when called from the fbdev driver,
> and just grab the lock again after the device has been registered and do
> a removal loop restart.
> 
> Since the framebuffer devices will already be removed, the loop would just
> finish when no more conflicting framebuffers are found.
> 
> Suggested-by: Daniel Vetter <daniel.vetter@...ll.ch>
> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
> Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>
> ---
Pushed this to drm-misc (drm-misc-next). Thanks all!

-- 
Best regards,

Javier Martinez Canillas
Linux Engineering
Red Hat