[Intel-gfx] [PATCH 01/12] drm/i915: Take rcu_read_lock for querying fence's driver/timeline names

[Daniel Vetter]

On Wed, May 26, 2021 at 03:14:45PM +0100, Tvrtko Ursulin wrote:
> From: Chris Wilson <chris at chris-wilson.co.uk>
> 
> The name very often may be freed independently of the fence, with the
> only protection being RCU. To be safe as we read the names, hold RCU.

Yeah no.

If it's not clear why, figure it out first.
-Daniel

> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Reviewed-by: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_sw_fence.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_sw_fence.c b/drivers/gpu/drm/i915/i915_sw_fence.c
> index 2744558f3050..dfabf291e5cd 100644
> --- a/drivers/gpu/drm/i915/i915_sw_fence.c
> +++ b/drivers/gpu/drm/i915/i915_sw_fence.c
> @@ -430,11 +430,13 @@ static void timer_i915_sw_fence_wake(struct timer_list *t)
>  	if (!fence)
>  		return;
>  
> +	rcu_read_lock();
>  	pr_notice("Asynchronous wait on fence %s:%s:%llx timed out (hint:%ps)\n",
>  		  cb->dma->ops->get_driver_name(cb->dma),
>  		  cb->dma->ops->get_timeline_name(cb->dma),
>  		  cb->dma->seqno,
>  		  i915_sw_fence_debug_hint(fence));
> +	rcu_read_unlock();
>  
>  	i915_sw_fence_set_error_once(fence, -ETIMEDOUT);
>  	i915_sw_fence_complete(fence);
> -- 
> 2.30.2
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch