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Date: Sat, 11 Jul 2026 15:26:18 +0200
Message-Id: <DJVRYBLM3B94.MAUO8T8NXM5P@kernel.org>
Cc: <christian.koenig@amd.com>, <thomas.hellstrom@linux.intel.com>,
 <ecourtney@nvidia.com>, <simona@ffwll.ch>, <matthew.brost@intel.com>,
 <nat@pixelcluster.dev>, <airlied@gmail.com>,
 <dri-devel@lists.freedesktop.org>, <linux-kernel@vger.kernel.org>,
 <intel-gfx@lists.freedesktop.org>, <intel-xe@lists.freedesktop.org>,
 <amd-gfx@lists.freedesktop.org>
To: =?utf-8?q?Christian_K=C3=B6nig?= <ckoenig.leichtzumerken@gmail.com>
From: "Danilo Krummrich" <dakr@kernel.org>
Subject: Re: [PATCH 09/12] drm/ttm: nuke buffer refcounting
References: <20260710190752.2355-1-christian.koenig@amd.com>
 <20260710190752.2355-10-christian.koenig@amd.com>
In-Reply-To: <20260710190752.2355-10-christian.koenig@amd.com>

On Fri Jul 10, 2026 at 8:52 PM CEST, =3D?UTF-8?q?Christian=3D20K=3DC3=3DB6n=
ig?=3D wrote:
> +/**
> + * ttm_bo_is_deleted - test if buffer is already deleted
> + * @bo: the struct ttm_buffer_object to test
> + *
> + * Returns true if the buffer is already deleted and only waiting for
> + * destruction.
> + */
> +static inline bool ttm_bo_is_deleted(struct ttm_buffer_object *bo)
> +{
> +	return !kref_read(&bo->base.refcount);
> +}

This is an anti-pattern, branch decisions cannot rely on an atomic referenc=
e
count unless additional invariants are upheld that otherwise guarantee that=
 the
read values does not instantly become meaningless.

Something like this should at least document in which context and under whi=
ch
conditions it is valid to rely on the returned value.