Re: [PATCH] drm/crc-debugfs: User irqsafe spinlock in drm_crtc_add_crc_entry

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

On Wed, Jun 05, 2019 at 09:45:56PM +0200, Daniel Vetter wrote:
> We can be called from any context, we need to be prepared.
> 
> Noticed this while hacking on vkms, which calls this function from a
> normal worker. Which really upsets lockdep.
> 
> Cc: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
> Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
> Cc: Emil Velikov <emil.velikov@collabora.com>
> Cc: Benjamin Gaignard <benjamin.gaignard@linaro.org>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

> ---
>  drivers/gpu/drm/drm_debugfs_crc.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_debugfs_crc.c b/drivers/gpu/drm/drm_debugfs_crc.c
> index 585169f0dcc5..7f35b5ba1924 100644
> --- a/drivers/gpu/drm/drm_debugfs_crc.c
> +++ b/drivers/gpu/drm/drm_debugfs_crc.c
> @@ -396,8 +396,9 @@ int drm_crtc_add_crc_entry(struct drm_crtc *crtc, bool has_frame,
>  	struct drm_crtc_crc *crc = &crtc->crc;
>  	struct drm_crtc_crc_entry *entry;
>  	int head, tail;
> +	unsigned long flags;
>  
> -	spin_lock(&crc->lock);
> +	spin_lock_irqsave(&crc->lock, flags);
>  
>  	/* Caller may not have noticed yet that userspace has stopped reading */
>  	if (!crc->entries) {
> @@ -428,7 +429,7 @@ int drm_crtc_add_crc_entry(struct drm_crtc *crtc, bool has_frame,
>  	head = (head + 1) & (DRM_CRC_ENTRIES_NR - 1);
>  	crc->head = head;
>  
> -	spin_unlock(&crc->lock);
> +	spin_unlock_irqrestore(&crc->lock, flags);
>  
>  	wake_up_interruptible(&crc->wq);
>  
> -- 
> 2.20.1
> 
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> dri-devel@lists.freedesktop.org
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-- 
Ville Syrjälä
Intel
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