Re: [PATCH 5/8] dma-buf: further relax reservation_object_add_shared_fence

From: Chris Wilson <chris@chris-wilson.co.uk>
To: "Christian König" <ckoenig.leichtzumerken@gmail.com>,
	dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org,
	linaro-mm-sig@lists.linaro.org
Subject: Re: [PATCH 5/8] dma-buf: further relax reservation_object_add_shared_fence
Date: Tue, 06 Aug 2019 20:25:54 +0100	[thread overview]
Message-ID: <156511955431.6198.11016206792697073807@skylake-alporthouse-com> (raw)
In-Reply-To: <20190806150134.104222-5-christian.koenig@amd.com>

Quoting Christian König (2019-08-06 16:01:31)
> Other cores don't busy wait any more and we removed the last user of checking
> the seqno for changes. Drop updating the number for shared fences altogether.
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>
> ---
>  drivers/dma-buf/reservation.c                    | 6 ------
>  drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c | 7 +------
>  2 files changed, 1 insertion(+), 12 deletions(-)
> 
> diff --git a/drivers/dma-buf/reservation.c b/drivers/dma-buf/reservation.c
> index c0ba05936ab6..944d962ddddf 100644
> --- a/drivers/dma-buf/reservation.c
> +++ b/drivers/dma-buf/reservation.c
> @@ -237,9 +237,6 @@ void reservation_object_add_shared_fence(struct reservation_object *obj,
>         fobj = reservation_object_get_list(obj);
>         count = fobj->shared_count;
>  
> -       preempt_disable();
> -       write_seqcount_begin(&obj->seq);
> -
>         for (i = 0; i < count; ++i) {
>  
>                 old = rcu_dereference_protected(fobj->shared[i],
> @@ -257,9 +254,6 @@ void reservation_object_add_shared_fence(struct reservation_object *obj,
>         RCU_INIT_POINTER(fobj->shared[i], fence);
>         /* pointer update must be visible before we extend the shared_count */
>         smp_store_mb(fobj->shared_count, count);

Yup, that's all the mb rules we need to apply for the rcu readers to see
a consistent view.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
-Chris
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