Re: [PATCH -next] gpu: drm: Fix spinlock vblank_time_lock use error.

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Jul 22, 2020 at 01:05:27AM +0000, Xu Qiang wrote:
> The drm_handle_vblank function is in the interrupt context.
> Therefore, the spin lock vblank_time_lock is obtained
> from the interrupt context.
> 
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Xu Qiang <xuqiang36@huawei.com>
> ---
>  drivers/gpu/drm/drm_vblank.c | 17 ++++++++++-------
>  1 file changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> index f402c75b9d34..4ca63ff33a43 100644
> --- a/drivers/gpu/drm/drm_vblank.c
> +++ b/drivers/gpu/drm/drm_vblank.c
> @@ -229,10 +229,11 @@ static void drm_reset_vblank_timestamp(struct drm_device *dev, unsigned int pipe
>  {
>  	u32 cur_vblank;
>  	bool rc;
> +	unsigned long irqflags;
>  	ktime_t t_vblank;
>  	int count = DRM_TIMESTAMP_MAXRETRIES;
>  
> -	spin_lock(&dev->vblank_time_lock);
> +	spin_lock_irqsave(&dev->vblank_time_lock, irqflags);

Nak. This is always called with interrupts off, so no point on wasting
time saving/restoring the flags. And it's the same situation for all the
other cases you have below.

>  
>  	/*
>  	 * sample the current counter to avoid random jumps
> @@ -257,7 +258,7 @@ static void drm_reset_vblank_timestamp(struct drm_device *dev, unsigned int pipe
>  	 */
>  	store_vblank(dev, pipe, 1, t_vblank, cur_vblank);
>  
> -	spin_unlock(&dev->vblank_time_lock);
> +	spin_unlock_irqrestore(&dev->vblank_time_lock, irqflags);
>  }
>  
>  /*
> @@ -1106,11 +1107,12 @@ static int __enable_vblank(struct drm_device *dev, unsigned int pipe)
>  static int drm_vblank_enable(struct drm_device *dev, unsigned int pipe)
>  {
>  	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
> +	unsigned long irqflags;
>  	int ret = 0;
>  
>  	assert_spin_locked(&dev->vbl_lock);
>  
> -	spin_lock(&dev->vblank_time_lock);
> +	spin_lock_irqsave(&dev->vblank_time_lock, irqflags);
>  
>  	if (!vblank->enabled) {
>  		/*
> @@ -1136,7 +1138,7 @@ static int drm_vblank_enable(struct drm_device *dev, unsigned int pipe)
>  		}
>  	}
>  
> -	spin_unlock(&dev->vblank_time_lock);
> +	spin_unlock_irqrestore(&dev->vblank_time_lock, irqflags);
>  
>  	return ret;
>  }
> @@ -1917,6 +1919,7 @@ bool drm_handle_vblank(struct drm_device *dev, unsigned int pipe)
>  {
>  	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
>  	unsigned long irqflags;
> +	unsigned long irqflags_vblank;
>  	bool disable_irq;
>  
>  	if (drm_WARN_ON_ONCE(dev, !drm_dev_has_vblank(dev)))
> @@ -1931,18 +1934,18 @@ bool drm_handle_vblank(struct drm_device *dev, unsigned int pipe)
>  	 * vblank enable/disable, as this would cause inconsistent
>  	 * or corrupted timestamps and vblank counts.
>  	 */
> -	spin_lock(&dev->vblank_time_lock);
> +	spin_lock_irqsave(&dev->vblank_time_lock, irqflags_vblank);
>  
>  	/* Vblank irq handling disabled. Nothing to do. */
>  	if (!vblank->enabled) {
> -		spin_unlock(&dev->vblank_time_lock);
> +		spin_unlock_irqrestore(&dev->vblank_time_lock, irqflags_vblank);
>  		spin_unlock_irqrestore(&dev->event_lock, irqflags);
>  		return false;
>  	}
>  
>  	drm_update_vblank_count(dev, pipe, true);
>  
> -	spin_unlock(&dev->vblank_time_lock);
> +	spin_unlock_irqrestore(&dev->vblank_time_lock, irqflags_vblank);
>  
>  	wake_up(&vblank->queue);
>  
> -- 
> 2.25.0
> 
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-- 
Ville Syrjälä
Intel