[PATCH] drm: Require __GFP_NOFAIL for the legacy drm_modeset_lock_all

[Ville Syrjälä]

On Tue, Oct 31, 2017 at 11:55:35AM +0000, Chris Wilson wrote:
> To acquire all modeset locks requires a ww_ctx to be allocated. As this
> is the legacy path and the allocation small, to reduce the changes
> required (and complex untested error handling) to the legacy drivers, we
> simply assume that the allocation succeeds. At present, it relies on the
> too-small-to-fail rule, but syzbot found that by injecting a failure
> here we would hit the WARN. Document that this allocation must succeed
> with __GFP_NOFAIL.
> 
> Reported-by: syzbot (syzkaller)
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>

Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>

> ---
> Resent to the right list!
> ---
>  drivers/gpu/drm/drm_modeset_lock.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_modeset_lock.c b/drivers/gpu/drm/drm_modeset_lock.c
> index e123497da0ca..963e23db0fe7 100644
> --- a/drivers/gpu/drm/drm_modeset_lock.c
> +++ b/drivers/gpu/drm/drm_modeset_lock.c
> @@ -93,7 +93,7 @@ void drm_modeset_lock_all(struct drm_device *dev)
>  	struct drm_modeset_acquire_ctx *ctx;
>  	int ret;
>  
> -	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
> +	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL | __GFP_NOFAIL);
>  	if (WARN_ON(!ctx))
>  		return;
>  
> -- 
> 2.15.0.rc2
> 
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-- 
Ville Syrjälä
Intel OTC