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Mon, 22 Apr 2024 06:41:05 +0000 (UTC) Date: Mon, 22 Apr 2024 08:41:03 +0200 From: Boris Brezillon To: =?UTF-8?B?QWRyacOhbg==?= Larumbe Cc: Rob Herring , Steven Price , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Daniel Vetter , Sumit Semwal , Christian =?UTF-8?B?S8O2bmln?= , Zack Rusin , Dmitry Osipenko , kernel@collabora.com, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org Subject: Re: [PATCH] drm/panfrost: Fix dma_resv deadlock at drm object pin time Message-ID: <20240422084103.1a9fbef6@collabora.com> In-Reply-To: <20240421163951.3398622-1-adrian.larumbe@collabora.com> References: <20240421163951.3398622-1-adrian.larumbe@collabora.com> Organization: Collabora X-Mailer: Claws Mail 4.2.0 (GTK 3.24.41; x86_64-redhat-linux-gnu) Precedence: bulk X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Sun, 21 Apr 2024 17:39:47 +0100 Adri=C3=A1n Larumbe wrote: > When Panfrost must pin an object that is being prepared a dma-buf > attachment for on behalf of another driver, the core drm gem object pinni= ng > code already takes a lock on the object's dma reservation. >=20 > However, Panfrost GEM object's pinning callback would eventually try taki= ng > the lock on the same dma reservation when delegating pinning of the object > onto the shmem subsystem, which led to a deadlock. >=20 > This can be shown by enabling CONFIG_DEBUG_WW_MUTEX_SLOWPATH, which throws > the following recursive locking situation: >=20 > weston/3440 is trying to acquire lock: > ffff000000e235a0 (reservation_ww_class_mutex){+.+.}-{3:3}, at: drm_gem_sh= mem_pin+0x34/0xb8 [drm_shmem_helper] > but task is already holding lock: > ffff000000e235a0 (reservation_ww_class_mutex){+.+.}-{3:3}, at: drm_gem_pi= n+0x2c/0x80 [drm] >=20 > Fix it by assuming the object's reservation had already been locked by the > time we reach panfrost_gem_pin. >=20 > Cc: Thomas Zimmermann > Cc: Dmitry Osipenko > Cc: Boris Brezillon > Cc: Steven Price > Fixes: a78027847226 ("drm/gem: Acquire reservation lock in drm_gem_{pin/u= npin}()") > Signed-off-by: Adri=C3=A1n Larumbe Reviewed-by: Boris Brezillon > --- > drivers/gpu/drm/panfrost/panfrost_gem.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) >=20 > diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/pa= nfrost/panfrost_gem.c > index d47b40b82b0b..6c26652d425d 100644 > --- a/drivers/gpu/drm/panfrost/panfrost_gem.c > +++ b/drivers/gpu/drm/panfrost/panfrost_gem.c > @@ -192,7 +192,12 @@ static int panfrost_gem_pin(struct drm_gem_object *o= bj) > if (bo->is_heap) > return -EINVAL; > =20 > - return drm_gem_shmem_pin(&bo->base); > + /* > + * Pinning can only happen in response to a prime attachment request fr= om > + * another driver, but that's already being handled by drm_gem_pin > + */ > + drm_WARN_ON(obj->dev, obj->import_attach); > + return drm_gem_shmem_pin_locked(&bo->base); > } > =20 > static enum drm_gem_object_status panfrost_gem_status(struct drm_gem_obj= ect *obj) >=20 > base-commit: 04687bff66b8a4b22748aa7215d3baef0b318e5b