On Thu, Nov 30, 2023 at 05:40:55PM -0800, Paloma Arellano wrote:
> Add a missing mutex lock to control vblank irq. Thus prevent race
> conditions when registering/unregistering the irq callback.
>
I'm guessing that the mutex is needed because vblank_refcount, while
being an atomic_t, doesn't actually provide any protection during
concurrency?
I also tried to follow the calls backwards, but I'm uncertain how you
end up here concurrently.
When wrapped in proper mutual exclusion, can't vblank_refcount just be
turned into an "int"...given that you're not actually able to rely on
it's atomic behavior anyways...
So, please rewrite the commit message with a detailed description of how
the concurrency happens, and please review if vblank_refcount should be
an atomic at all...
> v2: Slightly changed wording of commit message
> v3: Mistakenly did not change wording in last version. It is done now.
>
> Signed-off-by: Paloma Arellano <quic_parellan@xxxxxxxxxxx>
> ---
> drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c | 6 ++++++
> drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys.h | 6 ++++++
> drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_cmd.c | 2 ++
> drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c | 2 ++
> 4 files changed, 16 insertions(+)
>
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> index 1cf7ff6caff4e..19ff7d1d5ccad 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> @@ -119,6 +119,8 @@ enum dpu_enc_rc_states {
> * Virtual encoder defers as much as possible to the physical encoders.
> * Virtual encoder registers itself with the DRM Framework as the encoder.
> * @base: drm_encoder base class for registration with DRM
> + * @vblank_ctl_lock: Vblank ctl mutex lock to protect physical encoder
> + * for IRQ purposes
I think this protects vblank_refcount, so state that instead of the
vague "for IRQ purposes".
> * @enc_spinlock: Virtual-Encoder-Wide Spin Lock for IRQ purposes
> * @enabled: True if the encoder is active, protected by enc_lock
> * @num_phys_encs: Actual number of physical encoders contained.
> @@ -166,6 +168,7 @@ enum dpu_enc_rc_states {
> */
> struct dpu_encoder_virt {
> struct drm_encoder base;
> + struct mutex vblank_ctl_lock;
> spinlock_t enc_spinlock;
>
> bool enabled;
> @@ -2255,6 +2258,7 @@ static int dpu_encoder_setup_display(struct dpu_encoder_virt *dpu_enc,
> phys_params.dpu_kms = dpu_kms;
> phys_params.parent = &dpu_enc->base;
> phys_params.enc_spinlock = &dpu_enc->enc_spinlock;
> + phys_params.vblank_ctl_lock = &dpu_enc->vblank_ctl_lock;
>
> WARN_ON(disp_info->num_of_h_tiles < 1);
>
> @@ -2386,6 +2390,7 @@ struct drm_encoder *dpu_encoder_init(struct drm_device *dev,
> dpu_enc->enabled = false;
> mutex_init(&dpu_enc->enc_lock);
> mutex_init(&dpu_enc->rc_lock);
> + mutex_init(&dpu_enc->vblank_ctl_lock);
Is this somehow propagated to multiple different dpu_encoder_phys
instances, or why do you need to initialize it here and pass the pointer
through 2 different intermediate structures before assigning it to
phys_enc->vblank_ctl_lock below?
>
> ret = dpu_encoder_setup_display(dpu_enc, dpu_kms, disp_info);
> if (ret)
> @@ -2495,6 +2500,7 @@ void dpu_encoder_phys_init(struct dpu_encoder_phys *phys_enc,
> phys_enc->dpu_kms = p->dpu_kms;
> phys_enc->split_role = p->split_role;
> phys_enc->enc_spinlock = p->enc_spinlock;
> + phys_enc->vblank_ctl_lock = p->vblank_ctl_lock;
Could you not just mutex_init() the one and only vblank_ctl_lock here?
> phys_enc->enable_state = DPU_ENC_DISABLED;
>
> atomic_set(&phys_enc->vblank_refcount, 0);
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys.h b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys.h
> index 6f04c3d56e77c..5691bf6b82ee6 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys.h
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys.h
> @@ -155,6 +155,8 @@ enum dpu_intr_idx {
> * @hw_wb: Hardware interface to the wb registers
> * @dpu_kms: Pointer to the dpu_kms top level
> * @cached_mode: DRM mode cached at mode_set time, acted on in enable
> + * @vblank_ctl_lock: Vblank ctl mutex lock to protect physical encoder
> + * for IRQ purposes
Same here.
> * @enabled: Whether the encoder has enabled and running a mode
> * @split_role: Role to play in a split-panel configuration
> * @intf_mode: Interface mode
> @@ -183,6 +185,7 @@ struct dpu_encoder_phys {
> struct dpu_hw_wb *hw_wb;
> struct dpu_kms *dpu_kms;
> struct drm_display_mode cached_mode;
> + struct mutex *vblank_ctl_lock;
> enum dpu_enc_split_role split_role;
> enum dpu_intf_mode intf_mode;
> spinlock_t *enc_spinlock;
> @@ -253,6 +256,8 @@ struct dpu_encoder_phys_cmd {
> * @split_role: Role to play in a split-panel configuration
> * @hw_intf: Hardware interface to the intf registers
> * @hw_wb: Hardware interface to the wb registers
> + * @vblank_ctl_lock: Vblank ctl mutex lock to protect physical encoder
> + * for IRQ purposes
And here...
Regards,
Bjorn
> * @enc_spinlock: Virtual-Encoder-Wide Spin Lock for IRQ purposes
> */
> struct dpu_enc_phys_init_params {
> @@ -261,6 +266,7 @@ struct dpu_enc_phys_init_params {
> enum dpu_enc_split_role split_role;
> struct dpu_hw_intf *hw_intf;
> struct dpu_hw_wb *hw_wb;
> + struct mutex *vblank_ctl_lock;
> spinlock_t *enc_spinlock;
> };
>
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_cmd.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_cmd.c
> index 25babfe1f001a..dcf1f6a18ad6e 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_cmd.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_cmd.c
> @@ -244,6 +244,7 @@ static int dpu_encoder_phys_cmd_control_vblank_irq(
> return -EINVAL;
> }
>
> + mutex_lock(phys_enc->vblank_ctl_lock);
> refcount = atomic_read(&phys_enc->vblank_refcount);
>
> /* Slave encoders don't report vblank */
> @@ -275,6 +276,7 @@ static int dpu_encoder_phys_cmd_control_vblank_irq(
> }
>
> end:
> + mutex_unlock(phys_enc->vblank_ctl_lock);
> if (ret) {
> DRM_ERROR("vblank irq err id:%u pp:%d ret:%d, enable %s/%d\n",
> DRMID(phys_enc->parent),
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
> index 8e905d7267f9f..87bb49763785d 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
> @@ -364,6 +364,7 @@ static int dpu_encoder_phys_vid_control_vblank_irq(
> int ret = 0;
> int refcount;
>
> + mutex_lock(phys_enc->vblank_ctl_lock);
> refcount = atomic_read(&phys_enc->vblank_refcount);
>
> /* Slave encoders don't report vblank */
> @@ -394,6 +395,7 @@ static int dpu_encoder_phys_vid_control_vblank_irq(
> }
>
> end:
> + mutex_unlock(phys_enc->vblank_ctl_lock);
> if (ret) {
> DRM_ERROR("failed: id:%u intf:%d ret:%d enable:%d refcnt:%d\n",
> DRMID(phys_enc->parent),
> --
> 2.41.0
>
>
