[Intel-xe] [PATCH] drm/xe: Fix engine lookup refcount race

[Matthew Auld]

On Thu, 25 May 2023 at 09:16, Thomas Hellström
<thomas.hellstrom at linux.intel.com> wrote:
>
> Fix a race where the engine could disappear between lookup unlock and
> xe_engine_get().
>
> Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> ---
>  drivers/gpu/drm/xe/xe_engine.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/xe/xe_engine.c b/drivers/gpu/drm/xe/xe_engine.c
> index 094ec17d3004..3a400a546dfe 100644
> --- a/drivers/gpu/drm/xe/xe_engine.c
> +++ b/drivers/gpu/drm/xe/xe_engine.c
> @@ -161,10 +161,9 @@ struct xe_engine *xe_engine_lookup(struct xe_file *xef, u32 id)
>
>         mutex_lock(&xef->engine.lock);
>         e = xa_load(&xef->engine.xa, id);
> -       mutex_unlock(&xef->engine.lock);
> -
>         if (e)
>                 xe_engine_get(e);
> +       mutex_unlock(&xef->engine.lock);

Makes sense to me.

Reviewed-by: Matthew Auld <matthew.auld at intel.com>

But looking around a bit, why does engine_get_property_ioctl() not use
this? It also does a raw xa_load() and then touches the engine without
holding the lock or keeping a ref?

>
>         return e;
>  }

> --
> 2.39.2
>