linux-kernel - Re: [Freedreno] [PATCH] drm/msm/atomic: Drop per-CRTC locks in reverse order

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Message-ID: <185473dc6ac6abc9a343db07a1031170@codeaurora.org>
Date:   Tue, 20 Oct 2020 17:48:24 -0700
From:   abhinavk@...eaurora.org
To:     Rob Clark <robdclark@...il.com>
Cc:     dri-devel@...ts.freedesktop.org,
        Rob Clark <robdclark@...omium.org>,
        Krishna Manikandan <mkrishn@...eaurora.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <linux-arm-msm@...r.kernel.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        open list <linux-kernel@...r.kernel.org>,
        Maxime Ripard <mripard@...nel.org>,
        Daniel Vetter <daniel@...ll.ch>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <freedreno@...ts.freedesktop.org>, Sean Paul <sean@...rly.run>
Subject: Re: [Freedreno] [PATCH] drm/msm/atomic: Drop per-CRTC locks in
 reverse order

On 2020-10-20 15:26, Rob Clark wrote:
> From: Rob Clark <robdclark@...omium.org>
> 
> lockdep dislikes seeing locks unwound in a non-nested fashion.
> 
> Fixes: 37c2016e3608 ("drm/msm: Fix race condition in msm driver with
> async layer updates")
> Signed-off-by: Rob Clark <robdclark@...omium.org>
Reviewed-by: Abhinav Kumar <abhinavk@...eaurora.org>
> ---
>  drivers/gpu/drm/msm/msm_atomic.c |  2 +-
>  drivers/gpu/drm/msm/msm_kms.h    |  4 ++++
>  include/drm/drm_crtc.h           | 10 ++++++++++
>  3 files changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/msm/msm_atomic.c 
> b/drivers/gpu/drm/msm/msm_atomic.c
> index b03d6ab6b19b..6a326761dc4a 100644
> --- a/drivers/gpu/drm/msm/msm_atomic.c
> +++ b/drivers/gpu/drm/msm/msm_atomic.c
> @@ -67,7 +67,7 @@ static void unlock_crtcs(struct msm_kms *kms,
> unsigned int crtc_mask)
>  {
>  	struct drm_crtc *crtc;
> 
> -	for_each_crtc_mask(kms->dev, crtc, crtc_mask)
> +	for_each_crtc_mask_reverse(kms->dev, crtc, crtc_mask)
>  		mutex_unlock(&kms->commit_lock[drm_crtc_index(crtc)]);
>  }
> 
> diff --git a/drivers/gpu/drm/msm/msm_kms.h 
> b/drivers/gpu/drm/msm/msm_kms.h
> index 8d3e626c9fee..d8151a89e163 100644
> --- a/drivers/gpu/drm/msm/msm_kms.h
> +++ b/drivers/gpu/drm/msm/msm_kms.h
> @@ -211,4 +211,8 @@ int dpu_mdss_init(struct drm_device *dev);
>  	drm_for_each_crtc(crtc, dev) \
>  		for_each_if (drm_crtc_mask(crtc) & (crtc_mask))
> 
> +#define for_each_crtc_mask_reverse(dev, crtc, crtc_mask) \
> +	drm_for_each_crtc_reverse(crtc, dev) \
> +		for_each_if (drm_crtc_mask(crtc) & (crtc_mask))
> +
>  #endif /* __MSM_KMS_H__ */
> diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
> index dfdb04619b0d..25f5958f2882 100644
> --- a/include/drm/drm_crtc.h
> +++ b/include/drm/drm_crtc.h
> @@ -1274,4 +1274,14 @@ static inline struct drm_crtc
> *drm_crtc_find(struct drm_device *dev,
>  #define drm_for_each_crtc(crtc, dev) \
>  	list_for_each_entry(crtc, &(dev)->mode_config.crtc_list, head)
> 
> +/**
> + * drm_for_each_crtc_reverse - iterate over all CRTCs in reverse order
> + * @crtc: a &struct drm_crtc as the loop cursor
> + * @dev: the &struct drm_device
> + *
> + * Iterate over all CRTCs of @dev.
> + */
> +#define drm_for_each_crtc_reverse(crtc, dev) \
> +	list_for_each_entry_reverse(crtc, &(dev)->mode_config.crtc_list, 
> head)
> +
>  #endif /* __DRM_CRTC_H__ */