linux-kernel - Re: [PATCH v13 01/10] drm/shmem-helper: Switch to reservation lock

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Message-ID: <6b5644cf-6229-f99b-d429-a45d724493ee@collabora.com>
Date:   Wed, 15 Mar 2023 16:46:04 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     David Airlie <airlied@...il.com>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Gurchetan Singh <gurchetansingh@...omium.org>,
        Chia-I Wu <olvaffe@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        Daniel Almeida <daniel.almeida@...labora.com>,
        Gustavo Padovan <gustavo.padovan@...labora.com>,
        Daniel Stone <daniel@...ishbar.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Qiang Yu <yuq825@...il.com>,
        Steven Price <steven.price@....com>,
        Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>,
        Rob Herring <robh@...nel.org>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        kernel@...labora.com, virtualization@...ts.linux-foundation.org,
        intel-gfx@...ts.freedesktop.org
Subject: Re: [PATCH v13 01/10] drm/shmem-helper: Switch to reservation lock

On 3/14/23 05:26, Dmitry Osipenko wrote:
> @@ -633,7 +605,10 @@ int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct vm_area_struct
>  		return ret;
>  	}
>  
> +	dma_resv_lock(shmem->base.resv, NULL);
>  	ret = drm_gem_shmem_get_pages(shmem);
> +	dma_resv_unlock(shmem->base.resv);

Intel CI reported locking problem [1] here. It actually was also
reported for v12, but I missed that report because of the other noisy
reports.

[1]
https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_114671v2/shard-snb5/igt@prime_vgem@sync@rcs0.html

The test does the following:

1. creates vgem
2. export it do dmabuf
3. mmaps dmabuf

There is an obvious deadlock there. The DRM code assumes that mmap() is
unlocked, while for dma-buf it's locked. I'll see how to fix it for v14.

-- 
Best regards,
Dmitry