Re: [PATCH] drm/i915: Use rcu to defer freeing of irq_work

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 13/12/2017 09:48, Chris Wilson wrote:
> It is illegal to perform an immediate free of the struct irq_work from
> inside the irq_work callback (as irq_work_run_list modifies work->flags
> after execution of the work->func()). As we use the irq_work to
> coordinate the freeing of the callback from two different softirq paths,
> we need to defer the kfree from inside our irq_work callback, for which
> we can use kfree_rcu.
> 
> Fixes: 81c0ed21aa91 ("drm/i915/fence: Avoid del_timer_sync() from inside a timer")
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> ---
>   drivers/gpu/drm/i915/i915_sw_fence.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_sw_fence.c b/drivers/gpu/drm/i915/i915_sw_fence.c
> index e8ca67a129d2..ac236b88c99c 100644
> --- a/drivers/gpu/drm/i915/i915_sw_fence.c
> +++ b/drivers/gpu/drm/i915/i915_sw_fence.c
> @@ -367,6 +367,7 @@ struct i915_sw_dma_fence_cb {
>   	struct dma_fence *dma;
>   	struct timer_list timer;
>   	struct irq_work work;
> +	struct rcu_head rcu;
>   };
>   
>   static void timer_i915_sw_fence_wake(struct timer_list *t)
> @@ -406,7 +407,7 @@ static void irq_i915_sw_fence_work(struct irq_work *wrk)
>   	del_timer_sync(&cb->timer);
>   	dma_fence_put(cb->dma);
>   
> -	kfree(cb);
> +	kfree_rcu(cb, rcu);
>   }
>   
>   int i915_sw_fence_await_dma_fence(struct i915_sw_fence *fence,
> 

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko
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