linux-kernel - Re: [PATCH] drm/shmem-helper: Fix locking for drm_gem_shmem_get_pages

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Date:   Mon, 6 Feb 2023 19:47:13 +0100
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Asahi Lina <lina@...hilina.net>,
        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>
Cc:     linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Noralf Trønnes <noralf@...nnes.org>,
        asahi@...ts.linux.dev, Alyssa Rosenzweig <alyssa@...enzweig.io>
Subject: Re: [PATCH] drm/shmem-helper: Fix locking for
 drm_gem_shmem_get_pages_sgt()

Hello Lina,

On 2/5/23 13:51, Asahi Lina wrote:
> Other functions touching shmem->sgt take the pages lock, so do that here
> too. drm_gem_shmem_get_pages() & co take the same lock, so move to the
> _locked() variants to avoid recursive locking.
> 
> Discovered while auditing locking to write the Rust abstractions.
> 
> Fixes: 2194a63a818d ("drm: Add library for shmem backed GEM objects")
> Fixes: 4fa3d66f132b ("drm/shmem: Do dma_unmap_sg before purging pages")
> Signed-off-by: Asahi Lina <lina@...hilina.net>
> ---

Good catch. The patch looks good to me.

Reviewed-by: Javier Martinez Canillas <javierm@...hat.com>

What about drm_gem_shmem_free() BTW, I believe that the helper should also
grab the lock before unmap / free the sgtable?

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat