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Date: Thu, 2 May 2024 13:14:19 +0200
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Subject: Re: [PATCH v3 1/2] drm/panfrost: Fix dma_resv deadlock at drm object
 pin time
To: =?UTF-8?Q?Adri=C3=A1n_Larumbe?= <adrian.larumbe@collabora.com>,
 Qiang Yu <yuq825@gmail.com>,
 Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
 Maxime Ripard <mripard@kernel.org>, David Airlie <airlied@gmail.com>,
 Daniel Vetter <daniel@ffwll.ch>,
 Boris Brezillon <boris.brezillon@collabora.com>,
 Rob Herring <robh@kernel.org>, Steven Price <steven.price@arm.com>,
 Sumit Semwal <sumit.semwal@linaro.org>,
 Christian Koenig= <christian.koenig@amd.com>,
 Dmitry Osipenko <dmitry.osipenko@collabora.com>,
 Zack Rusin <zack.rusin@broadcom.com>
Cc: kernel@collabora.com, dri-devel@lists.freedesktop.org,
 lima@lists.freedesktop.org, linux-kernel@vger.kernel.org,
 linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org
References: <20240501065650.2809530-1-adrian.larumbe@collabora.com>
 <20240501065650.2809530-2-adrian.larumbe@collabora.com>
Content-Language: en-US
From: Thomas Zimmermann <tzimmermann@suse.de>
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In-Reply-To: <20240501065650.2809530-2-adrian.larumbe@collabora.com>
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Hi

Am 01.05.24 um 08:55 schrieb Adrián Larumbe:
> 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 pinning
> code already takes a lock on the object's dma reservation.
>
> However, Panfrost GEM object's pinning callback would eventually try taking
> the lock on the same dma reservation when delegating pinning of the object
> onto the shmem subsystem, which led to a deadlock.
>
> This can be shown by enabling CONFIG_DEBUG_WW_MUTEX_SLOWPATH, which throws
> the following recursive locking situation:
>
> weston/3440 is trying to acquire lock:
> ffff000000e235a0 (reservation_ww_class_mutex){+.+.}-{3:3}, at: drm_gem_shmem_pin+0x34/0xb8 [drm_shmem_helper]
> but task is already holding lock:
> ffff000000e235a0 (reservation_ww_class_mutex){+.+.}-{3:3}, at: drm_gem_pin+0x2c/0x80 [drm]
>
> Fix it by assuming the object's reservation had already been locked by the
> time we reach panfrost_gem_pin.

Maybe say that the reservation lock has been taken in drm_gem_pin()

>
> Do the same thing for the Lima driver, as it most likely suffers from the
> same issue.

Please split this patch into one for panfrost and one for lima. To each 
patch, you can add

Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>

Best regards
Thomas

>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> Cc: Boris Brezillon <boris.brezillon@collabora.com>
> Cc: Steven Price <steven.price@arm.com>
> Fixes: a78027847226 ("drm/gem: Acquire reservation lock in drm_gem_{pin/unpin}()")
> Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
> ---
>   drivers/gpu/drm/lima/lima_gem.c         | 2 +-
>   drivers/gpu/drm/panfrost/panfrost_gem.c | 2 +-
>   2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/lima/lima_gem.c b/drivers/gpu/drm/lima/lima_gem.c
> index 7ea244d876ca..c4e0f9faaa47 100644
> --- a/drivers/gpu/drm/lima/lima_gem.c
> +++ b/drivers/gpu/drm/lima/lima_gem.c
> @@ -185,7 +185,7 @@ static int lima_gem_pin(struct drm_gem_object *obj)
>   	if (bo->heap_size)
>   		return -EINVAL;
>   
> -	return drm_gem_shmem_pin(&bo->base);
> +	return drm_gem_shmem_object_pin(obj);
>   }
>   
>   static int lima_gem_vmap(struct drm_gem_object *obj, struct iosys_map *map)
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c
> index d47b40b82b0b..f268bd5c2884 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gem.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.c
> @@ -192,7 +192,7 @@ static int panfrost_gem_pin(struct drm_gem_object *obj)
>   	if (bo->is_heap)
>   		return -EINVAL;
>   
> -	return drm_gem_shmem_pin(&bo->base);
> +	return drm_gem_shmem_object_pin(obj);
>   }
>   
>   static enum drm_gem_object_status panfrost_gem_status(struct drm_gem_object *obj)

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)