linux-kernel - Re: [PATCH] drm/irq: Add irq as false detection

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Message-ID: <8a76d144-f8ba-bbbc-9177-53088f6dc73a@suse.de>
Date:   Mon, 2 Nov 2020 13:09:39 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Tian Tao <tiantao6@...ilicon.com>,
        maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
        airlied@...ux.ie, daniel@...ll.ch, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/irq: Add irq as false detection

Hi

Am 02.11.20 um 12:19 schrieb Tian Tao:
> Add the detection of false for irq, so that the EINVAL is not
> returned when dev->irq_enabled is false.
> 
> Signed-off-by: Tian Tao <tiantao6@...ilicon.com>
> ---
>  drivers/gpu/drm/drm_irq.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
> index 09d6e9e..7537a3d 100644
> --- a/drivers/gpu/drm/drm_irq.c
> +++ b/drivers/gpu/drm/drm_irq.c
> @@ -172,6 +172,9 @@ int drm_irq_uninstall(struct drm_device *dev)
>  	bool irq_enabled;
>  	int i;
>  
> +	if (!dev->irq_enabled || !dev)
> +		return 0;
> +

Dereferencing a pointer before NULL-checking it, is Yoda programming. :)
I'd just drop the test for !dev and assume that dev is always valid.

I suggest to change the int return value to void and return nothing.

Re-reading the actual implementation of this function, this location
might be too early. Further below there already is a test for
irq_enabled. Put a drm_WARN_ON around it and it should be fine. This way
the vblank handlers will be disabled and erroneous callers will see a
warning in the kernel's log.

Best regards
Thomas

>  	irq_enabled = dev->irq_enabled;
>  	dev->irq_enabled = false;
>  
> 

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

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