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Message-ID: <20240422084103.1a9fbef6@collabora.com>
Date: Mon, 22 Apr 2024 08:41:03 +0200
From: Boris Brezillon <boris.brezillon@...labora.com>
To: Adrián Larumbe <adrian.larumbe@...labora.com>
Cc: Rob Herring <robh@...nel.org>, Steven Price <steven.price@....com>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard
<mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, David Airlie
<airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, Sumit Semwal
<sumit.semwal@...aro.org>, Christian König
<christian.koenig@....com>, Zack Rusin <zack.rusin@...adcom.com>, Dmitry
Osipenko <dmitry.osipenko@...labora.com>, kernel@...labora.com,
dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
linux-media@...r.kernel.org, linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH] drm/panfrost: Fix dma_resv deadlock at drm object pin
time
On Sun, 21 Apr 2024 17:39:47 +0100
Adrián Larumbe <adrian.larumbe@...labora.com> 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 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.
>
> Cc: Thomas Zimmermann <tzimmermann@...e.de>
> Cc: Dmitry Osipenko <dmitry.osipenko@...labora.com>
> Cc: Boris Brezillon <boris.brezillon@...labora.com>
> Cc: Steven Price <steven.price@....com>
> Fixes: a78027847226 ("drm/gem: Acquire reservation lock in drm_gem_{pin/unpin}()")
> Signed-off-by: Adrián Larumbe <adrian.larumbe@...labora.com>
Reviewed-by: Boris Brezillon <boris.brezillon@...labora.com>
> ---
> drivers/gpu/drm/panfrost/panfrost_gem.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/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 *obj)
> if (bo->is_heap)
> return -EINVAL;
>
> - return drm_gem_shmem_pin(&bo->base);
> + /*
> + * Pinning can only happen in response to a prime attachment request from
> + * 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);
> }
>
> static enum drm_gem_object_status panfrost_gem_status(struct drm_gem_object *obj)
>
> base-commit: 04687bff66b8a4b22748aa7215d3baef0b318e5b
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