Re: [PATCH] drm/xe: Fix exec IOCTL long running exec queue ring full condition

["Welty, Brian" <brian.welty@intel.com>]

On 1/4/2024 12:09 AM, Matthew Brost wrote:
> The intent is to return -EWOULDBLOCK to the user if a long running exec
> queue is full during the exec IOCTL. -EWOULDBLOCK aliases to -EAGAIN
> which results in the exec IOCTL doing a retry loop. Fix this by ensuring
> the retry loop is broken when returning -EWOULDBLOCK.
> 
> Fixes: 8ae8a2e8dd21 ("drm/xe: Long running job update")
> Reported-by: Sai Gowtham Ch <sai.gowtham.ch@intel.com>
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
>   drivers/gpu/drm/xe/xe_exec.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_exec.c b/drivers/gpu/drm/xe/xe_exec.c
> index d30c0d0689bc..c68e1bd15e6a 100644
> --- a/drivers/gpu/drm/xe/xe_exec.c
> +++ b/drivers/gpu/drm/xe/xe_exec.c
> @@ -115,7 +115,7 @@ int xe_exec_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
>   	struct xe_sched_job *job;
>   	struct dma_fence *rebind_fence;
>   	struct xe_vm *vm;
> -	bool write_locked;
> +	bool write_locked, skip_eagain = false;
>   	ktime_t end = 0;
>   	int err = 0;
>   
> @@ -227,7 +227,8 @@ int xe_exec_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
>   	}
>   
>   	if (xe_exec_queue_is_lr(q) && xe_exec_queue_ring_full(q)) {
> -		err = -EWOULDBLOCK;
> +		err = -EWOULDBLOCK;	/* Aliased to -EAGAIN */
> +		skip_eagain = true;

Would using another error code be more clean and avoid confusion in 
user-space as well?   Such as -EBUSY here?

But if you feel strongly about using EWOULDBLOCK, fix looks good to me.
Reviewed-by: Brian Welty <brian.welty@intel.com>

>   		goto err_exec;
>   	}
>   
> @@ -337,7 +338,7 @@ int xe_exec_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
>   		up_write(&vm->lock);
>   	else
>   		up_read(&vm->lock);
> -	if (err == -EAGAIN)
> +	if (err == -EAGAIN && !skip_eagain)
>   		goto retry;
>   err_syncs:
>   	for (i = 0; i < num_syncs; i++)