Re: [PATCH] drm/xe/ufence: Wake up waiters after setting ufence->signalled

[Matthew Brost <matthew.brost@intel.com>]

On Thu, Nov 14, 2024 at 04:05:37PM +0100, Nirmoy Das wrote:
> If a previous ufence is not signalled, vm_bind will return -EBUSY.
> Delaying the modification of ufence->signalled can cause issues if the
> UMD reuses the same ufence so update ufence->signalled before waking up
> waiters.
> 
> Cc: Matthew Brost <matthew.brost@intel.com>
> Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/3233

Do we need a fixes tag?

Reviewed-by: Matthew Brost <matthew.brost@intel.com>

> Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_sync.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_sync.c b/drivers/gpu/drm/xe/xe_sync.c
> index a90480c6aecf..42f5bebd09e5 100644
> --- a/drivers/gpu/drm/xe/xe_sync.c
> +++ b/drivers/gpu/drm/xe/xe_sync.c
> @@ -87,8 +87,12 @@ static void user_fence_worker(struct work_struct *w)
>  		drm_dbg(&ufence->xe->drm, "mmget_not_zero() failed, ufence wasn't signaled\n");
>  	}
>  
> -	wake_up_all(&ufence->xe->ufence_wq);
> +	/*
> +	 * Wake up waiters only after updating the ufence state, allowing the UMD
> +	 * to safely reuse the same ufence without encountering -EBUSY errors.
> +	 */
>  	WRITE_ONCE(ufence->signalled, 1);
> +	wake_up_all(&ufence->xe->ufence_wq);
>  	user_fence_put(ufence);
>  }
>  
> -- 
> 2.46.0
>