Re: [Freedreno] [PATCH v2 2/4] drm/msm: make msm_disp_state transient data struct

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On 2021-04-27 13:29, Dmitry Baryshkov wrote:
On Tue, 27 Apr 2021 at 22:19, <abhinavk@xxxxxxxxxxxxxx> wrote:

Hi Dmitry

On 2021-04-26 17:18, Dmitry Baryshkov wrote:
> Instead of allocating snapshotting structure at the driver probe time
> and later handling concurrent access, actual state, etc, make
> msm_disp_state transient struct. Allocate one when snapshotting happens
> and free it after coredump data is read by userspace.
>
Can you please check my previous comment on coredump_pending?

https://lore.kernel.org/dri-devel/186825e2fb7bea8d45f33b5c1fa3509f@xxxxxxxxxxxxxx/T/#u

That helps to serialize read/write of coredump.

Regarding the serialization of read/write. As the disp_state becomes
the transient object, the need for such serialization vanishes:
 - Before the snapshot is complete, the object is not linked outside
of msm_disp_snapshot functions.
 - When the snapshot is complete, it becomes linked from the codedump
subsystem. After this it is only read by the coredump, nobody will
write to it.
 - Next snapshot will allocate a new disp_state structure.
 - If dev_coredumpm is called when the previous snapshot is still
referenced (the device exists), the new snapshot is silently freed.

Thus there is no need to sync the read/write operations. They are now
naturally serialized.
Alright, just make sure to validate the robustness of this using the method mentioned earlier.
Apart from that,

Reviewed-by: Abhinav Kumar <abhinavk@xxxxxxxxxxxxxx>


Rest of the changes on this one look fine to me.

> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
> ---
>  drivers/gpu/drm/msm/disp/msm_disp_snapshot.c  | 90 ++++++-------------
>  drivers/gpu/drm/msm/disp/msm_disp_snapshot.h  | 13 +--
>  .../gpu/drm/msm/disp/msm_disp_snapshot_util.c |  5 +-
>  drivers/gpu/drm/msm/msm_kms.h                 |  6 +-
>  4 files changed, 37 insertions(+), 77 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/disp/msm_disp_snapshot.c
> b/drivers/gpu/drm/msm/disp/msm_disp_snapshot.c
> index 70fd5a1fe13e..a4a7cb06bc87 100644
> --- a/drivers/gpu/drm/msm/disp/msm_disp_snapshot.c
> +++ b/drivers/gpu/drm/msm/disp/msm_disp_snapshot.c
> @@ -7,8 +7,7 @@
>
>  #include "msm_disp_snapshot.h"
>
> -#ifdef CONFIG_DEV_COREDUMP
> -static ssize_t disp_devcoredump_read(char *buffer, loff_t offset,
> +static ssize_t __maybe_unused disp_devcoredump_read(char *buffer,
> loff_t offset,
>               size_t count, void *data, size_t datalen)
>  {
>       struct drm_print_iterator iter;
> @@ -29,52 +28,47 @@ static ssize_t disp_devcoredump_read(char *buffer,
> loff_t offset,
>       return count - iter.remain;
>  }
>
> -static void disp_devcoredump_free(void *data)
> +static void _msm_disp_snapshot_work(struct kthread_work *work)
>  {
> +     struct msm_kms *kms = container_of(work, struct msm_kms, dump_work);
> +     struct drm_device *drm_dev = kms->dev;
>       struct msm_disp_state *disp_state;
> +     struct drm_printer p;
>
> -     disp_state = data;
> -
> -     msm_disp_state_free(disp_state);
> +     disp_state = kzalloc(sizeof(struct msm_disp_state), GFP_KERNEL);
> +     if (!disp_state)
> +             return;
>
> -     disp_state->coredump_pending = false;
> -}
> -#endif /* CONFIG_DEV_COREDUMP */
> +     disp_state->dev = drm_dev->dev;
> +     disp_state->drm_dev = drm_dev;
>
> -static void _msm_disp_snapshot_work(struct kthread_work *work)
> -{
> -     struct msm_disp_state *disp_state = container_of(work, struct
> msm_disp_state, dump_work);
> -     struct drm_printer p;
> +     INIT_LIST_HEAD(&disp_state->blocks);
>
> -     mutex_lock(&disp_state->mutex);
> +     /* Serialize dumping here */
> +     mutex_lock(&kms->dump_mutex);
>
>       msm_disp_snapshot_capture_state(disp_state);
>
> +     mutex_unlock(&kms->dump_mutex);
> +
>       if (MSM_DISP_SNAPSHOT_DUMP_IN_CONSOLE) {
>               p = drm_info_printer(disp_state->drm_dev->dev);
>               msm_disp_state_print(disp_state, &p);
>       }
>
>       /*
> -      * if devcoredump is not defined free the state immediately
> -      * otherwise it will be freed in the free handler.
> +      * If COREDUMP is disabled, the stub will call the free function.
> +      * If there is a codedump pending for the device, the dev_coredumpm()
> +      * will also free new coredump state.
>        */
> -#ifdef CONFIG_DEV_COREDUMP
>       dev_coredumpm(disp_state->dev, THIS_MODULE, disp_state, 0,
> GFP_KERNEL,
> -                     disp_devcoredump_read, disp_devcoredump_free);
> -     disp_state->coredump_pending = true;
> -#else
> -     msm_disp_state_free(disp_state);
> -#endif
> -
> -     mutex_unlock(&disp_state->mutex);
> +                     disp_devcoredump_read, msm_disp_state_free);
>  }
>
>  void msm_disp_snapshot_state(struct drm_device *drm_dev)
>  {
>       struct msm_drm_private *priv;
>       struct msm_kms *kms;
> -     struct msm_disp_state *disp_state;
>
>       if (!drm_dev) {
>               DRM_ERROR("invalid params\n");
> @@ -83,30 +77,13 @@ void msm_disp_snapshot_state(struct drm_device
> *drm_dev)
>
>       priv = drm_dev->dev_private;
>       kms = priv->kms;
> -     disp_state = kms->disp_state;
> -
> -     if (!disp_state) {
> -             DRM_ERROR("invalid params\n");
> -             return;
> -     }
>
> -     /*
> -      * if there is a coredump pending return immediately till dump
> -      * if read by userspace or timeout happens
> -      */
> -     if (disp_state->coredump_pending) {
> -             DRM_DEBUG("coredump is pending read\n");
> -             return;
> -     }
> -
> -     kthread_queue_work(disp_state->dump_worker,
> -                     &disp_state->dump_work);
> +     kthread_queue_work(kms->dump_worker, &kms->dump_work);
>  }
>
>  int msm_disp_snapshot_init(struct drm_device *drm_dev)
>  {
>       struct msm_drm_private *priv;
> -     struct msm_disp_state *disp_state;
>       struct msm_kms *kms;
>
>       if (!drm_dev) {
> @@ -117,22 +94,13 @@ int msm_disp_snapshot_init(struct drm_device
> *drm_dev)
>       priv = drm_dev->dev_private;
>       kms = priv->kms;
>
> -     disp_state = devm_kzalloc(drm_dev->dev, sizeof(struct
> msm_disp_state), GFP_KERNEL);
> -
> -     mutex_init(&disp_state->mutex);
> +     mutex_init(&kms->dump_mutex);
>
> -     disp_state->dev = drm_dev->dev;
> -     disp_state->drm_dev = drm_dev;
> -
> -     INIT_LIST_HEAD(&disp_state->blocks);
> -
> -     disp_state->dump_worker = kthread_create_worker(0, "%s",
> "disp_snapshot");
> -     if (IS_ERR(disp_state->dump_worker))
> +     kms->dump_worker = kthread_create_worker(0, "%s", "disp_snapshot");
> +     if (IS_ERR(kms->dump_worker))
>               DRM_ERROR("failed to create disp state task\n");
>
> -     kthread_init_work(&disp_state->dump_work, _msm_disp_snapshot_work);
> -
> -     kms->disp_state = disp_state;
> +     kthread_init_work(&kms->dump_work, _msm_disp_snapshot_work);
>
>       return 0;
>  }
> @@ -141,7 +109,6 @@ void msm_disp_snapshot_destroy(struct drm_device
> *drm_dev)
>  {
>       struct msm_kms *kms;
>       struct msm_drm_private *priv;
> -     struct msm_disp_state *disp_state;
>
>       if (!drm_dev) {
>               DRM_ERROR("invalid params\n");
> @@ -150,12 +117,9 @@ void msm_disp_snapshot_destroy(struct drm_device
> *drm_dev)
>
>       priv = drm_dev->dev_private;
>       kms = priv->kms;
> -     disp_state = kms->disp_state;
> -
> -     if (disp_state->dump_worker)
> -             kthread_destroy_worker(disp_state->dump_worker);
>
> -     list_del(&disp_state->blocks);
> +     if (kms->dump_worker)
> +             kthread_destroy_worker(kms->dump_worker);
>
> -     mutex_destroy(&disp_state->mutex);
> +     mutex_destroy(&kms->dump_mutex);
>  }
> diff --git a/drivers/gpu/drm/msm/disp/msm_disp_snapshot.h
> b/drivers/gpu/drm/msm/disp/msm_disp_snapshot.h
> index 32f52799a1ba..c6174a366095 100644
> --- a/drivers/gpu/drm/msm/disp/msm_disp_snapshot.h
> +++ b/drivers/gpu/drm/msm/disp/msm_disp_snapshot.h
> @@ -41,26 +41,17 @@
>   * struct msm_disp_state - structure to store current dpu state
>   * @dev: device pointer
>   * @drm_dev: drm device pointer
> - * @mutex: mutex to serialize access to serialze dumps, debugfs access
> - * @coredump_pending: coredump is pending read from userspace
>   * @atomic_state: atomic state duplicated at the time of the error
> - * @dump_worker: kworker thread which runs the dump work
> - * @dump_work: kwork which dumps the registers and drm state
>   * @timestamp: timestamp at which the coredump was captured
>   */
>  struct msm_disp_state {
>       struct device *dev;
>       struct drm_device *drm_dev;
> -     struct mutex mutex;
> -
> -     bool coredump_pending;
>
>       struct list_head blocks;
>
>       struct drm_atomic_state *atomic_state;
>
> -     struct kthread_worker *dump_worker;
> -     struct kthread_work dump_work;
>       ktime_t timestamp;
>  };
>
> @@ -123,11 +114,11 @@ void msm_disp_snapshot_capture_state(struct
> msm_disp_state *disp_state);
>
>  /**
>   * msm_disp_state_free - free the memory after the coredump has been
> read
> - * @disp_state:          handle to struct msm_disp_state
> + * @data:        handle to struct msm_disp_state
>
>   * Returns: none
>   */
> -void msm_disp_state_free(struct msm_disp_state *disp_state);
> +void msm_disp_state_free(void *data);
>
>  /**
>   * msm_disp_snapshot_add_block - add a hardware block with its
> register dump
> diff --git a/drivers/gpu/drm/msm/disp/msm_disp_snapshot_util.c
> b/drivers/gpu/drm/msm/disp/msm_disp_snapshot_util.c
> index ca6632550337..cabe15190ec1 100644
> --- a/drivers/gpu/drm/msm/disp/msm_disp_snapshot_util.c
> +++ b/drivers/gpu/drm/msm/disp/msm_disp_snapshot_util.c
> @@ -142,8 +142,9 @@ void msm_disp_snapshot_capture_state(struct
> msm_disp_state *disp_state)
>       msm_disp_capture_atomic_state(disp_state);
>  }
>
> -void msm_disp_state_free(struct msm_disp_state *disp_state)
> +void msm_disp_state_free(void *data)
>  {
> +     struct msm_disp_state *disp_state = data;
>       struct msm_disp_state_block *block, *tmp;
>
>       if (disp_state->atomic_state) {
> @@ -156,6 +157,8 @@ void msm_disp_state_free(struct msm_disp_state
> *disp_state)
>               kfree(block->state);
>               kfree(block);
>       }
> +
> +     kfree(disp_state);
>  }
>
>  void msm_disp_snapshot_add_block(struct msm_disp_state *disp_state,
> u32 len,
> diff --git a/drivers/gpu/drm/msm/msm_kms.h
> b/drivers/gpu/drm/msm/msm_kms.h
> index 146dcab123f4..086a2d59b8c8 100644
> --- a/drivers/gpu/drm/msm/msm_kms.h
> +++ b/drivers/gpu/drm/msm/msm_kms.h
> @@ -156,8 +156,10 @@ struct msm_kms {
>       /* mapper-id used to request GEM buffer mapped for scanout: */
>       struct msm_gem_address_space *aspace;
>
> -     /* handle to disp snapshot state */
> -     struct msm_disp_state *disp_state;
> +     /* disp snapshot support */
> +     struct kthread_worker *dump_worker;
> +     struct kthread_work dump_work;
> +     struct mutex dump_mutex;
>
>       /*
>        * For async commit, where ->flush_commit() and later happens
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