Re: [PATCH] drm/xe: Do not access xe file when updating exec queue runtime

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Fri, May 24, 2024 at 11:49:58AM -0700, Umesh Nerlige Ramappa wrote:
> The current code is running into a use after free case where xe file is
> closed before the exec queue runtime can be updated. This is occuring in
> the xe_file_close path. To fix that, do not access xe file when updating
> the exec queue runtime. Instead store the exec queue runtime locally in
> the exec queue object and accumulate it when the user dumps the drm
> client stats. We know that the xe file is valid when user is dumping the
> runtime stats for the drm client, so this effectively removes the
> dependency on xe file object in xe_exec_queue_update_runtime().
> 
> Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/1908
> Fixes: 6109f24f87d7 ("drm/xe: Add helper to accumulate exec queue runtime")
> Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_drm_client.c       | 4 +++-
>  drivers/gpu/drm/xe/xe_exec_queue.c       | 5 +----
>  drivers/gpu/drm/xe/xe_exec_queue_types.h | 2 ++
>  3 files changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_drm_client.c b/drivers/gpu/drm/xe/xe_drm_client.c
> index af404c9e5cc0..a6a15562b8f7 100644
> --- a/drivers/gpu/drm/xe/xe_drm_client.c
> +++ b/drivers/gpu/drm/xe/xe_drm_client.c
> @@ -251,8 +251,10 @@ static void show_runtime(struct drm_printer *p, struct drm_file *file)
>  
>  	/* Accumulate all the exec queues from this client */
>  	mutex_lock(&xef->exec_queue.lock);
> -	xa_for_each(&xef->exec_queue.xa, i, q)
> +	xa_for_each(&xef->exec_queue.xa, i, q) {
>  		xe_exec_queue_update_runtime(q);
> +		xef->runtime[q->class] += q->runtime - xef->runtime[q->class];
> +	}
>  	mutex_unlock(&xef->exec_queue.lock);
>  
>  	/* Get the total GPU cycles */
> diff --git a/drivers/gpu/drm/xe/xe_exec_queue.c b/drivers/gpu/drm/xe/xe_exec_queue.c
> index 0fd61fb4d104..a0775a96efb1 100644
> --- a/drivers/gpu/drm/xe/xe_exec_queue.c
> +++ b/drivers/gpu/drm/xe/xe_exec_queue.c
> @@ -765,7 +765,6 @@ bool xe_exec_queue_is_idle(struct xe_exec_queue *q)
>   */
>  void xe_exec_queue_update_runtime(struct xe_exec_queue *q)
>  {
> -	struct xe_file *xef;
>  	struct xe_lrc *lrc;
>  	u32 old_ts, new_ts;
>  
> @@ -777,8 +776,6 @@ void xe_exec_queue_update_runtime(struct xe_exec_queue *q)
>  	if (!q->vm || !q->vm->xef)
>  		return;
>  
> -	xef = q->vm->xef;
> -
>  	/*
>  	 * Only sample the first LRC. For parallel submission, all of them are
>  	 * scheduled together and we compensate that below by multiplying by
> @@ -789,7 +786,7 @@ void xe_exec_queue_update_runtime(struct xe_exec_queue *q)
>  	 */
>  	lrc = &q->lrc[0];
>  	new_ts = xe_lrc_update_timestamp(lrc, &old_ts);
> -	xef->runtime[q->class] += (new_ts - old_ts) * q->width;
> +	q->runtime += (new_ts - old_ts) * q->width;
>  }
>  
>  void xe_exec_queue_kill(struct xe_exec_queue *q)
> diff --git a/drivers/gpu/drm/xe/xe_exec_queue_types.h b/drivers/gpu/drm/xe/xe_exec_queue_types.h
> index ee78d497d838..085a7dce7565 100644
> --- a/drivers/gpu/drm/xe/xe_exec_queue_types.h
> +++ b/drivers/gpu/drm/xe/xe_exec_queue_types.h
> @@ -151,6 +151,8 @@ struct xe_exec_queue {
>  	 * Protected by @vm's resv. Unused if @vm == NULL.
>  	 */
>  	u64 tlb_flush_seqno;
> +	/** @runtime: hw engine class runtime in ticks for this exec queue*/
                                                                          ^
missing space                                                             ^

good idea to move to the exec_queue

> +	u64 runtime;

could we please find a better name for this? runtime what?
or do you mean run_time?
Is this the total run time of the exec queue expressed in ticks of the eu clock?

My poor brain parses runtime as the phase of the operation, vs
run_time as the time spent running.

or perhaps 'run_ticks'?

>  	/** @lrc: logical ring context for this exec queue */
>  	struct xe_lrc lrc[];
>  };
> -- 
> 2.34.1
>