From: Daniel Vetter <daniel@ffwll.ch>
To: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
Cc: maarten.lankhorst@linux.intel.com, mripard@kernel.org,
tzimmermann@suse.de, airlied@linux.ie, daniel@ffwll.ch,
sumit.semwal@linaro.org, christian.koenig@amd.com,
axboe@kernel.dk, oleg@redhat.com, tglx@linutronix.de,
dvyukov@google.com, walter-zh.wu@mediatek.com,
dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
intel-gfx@lists.freedesktop.org, linux-media@vger.kernel.org,
linaro-mm-sig@lists.linaro.org, skhan@linuxfoundation.org,
gregkh@linuxfoundation.org,
linux-kernel-mentees@lists.linuxfoundation.org
Subject: Re: [PATCH v3 2/9] drm: hold master_lookup_lock when releasing a drm_file's master
Date: Wed, 18 Aug 2021 12:05:01 +0200 [thread overview]
Message-ID: <YRzbTUM8ggXlIEyr@phenom.ffwll.local> (raw)
In-Reply-To: <20210818073824.1560124-3-desmondcheongzx@gmail.com>
On Wed, Aug 18, 2021 at 03:38:17PM +0800, Desmond Cheong Zhi Xi wrote:
> When drm_file.master changes value, the corresponding
> drm_device.master_lookup_lock should be held.
>
> In drm_master_release, a call to drm_master_put sets the
> file_priv->master to NULL, so we protect this section with
> drm_device.master_lookup_lock.
>
> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
At this points all refcounts to drm_file have disappeared, so yeah this is
a lockless access, but also no one can observe it anymore. See also next
patch.
Hence I think the current code is fine.
-Daniel
> ---
> drivers/gpu/drm/drm_auth.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c
> index 8efb58aa7d95..8c0e0dba1611 100644
> --- a/drivers/gpu/drm/drm_auth.c
> +++ b/drivers/gpu/drm/drm_auth.c
> @@ -373,8 +373,11 @@ void drm_master_release(struct drm_file *file_priv)
> }
>
> /* drop the master reference held by the file priv */
> - if (file_priv->master)
> + if (file_priv->master) {
> + spin_lock(&dev->master_lookup_lock);
> drm_master_put(&file_priv->master);
> + spin_unlock(&dev->master_lookup_lock);
> + }
> mutex_unlock(&dev->master_mutex);
> }
>
> --
> 2.25.1
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
next prev parent reply other threads:[~2021-08-18 10:05 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-18 7:38 [PATCH v3 0/9] drm, kernel: update locking for DRM Desmond Cheong Zhi Xi
2021-08-18 7:38 ` [PATCH v3 1/9] drm: move master_lookup_lock into drm_device Desmond Cheong Zhi Xi
2021-08-18 7:38 ` [PATCH v3 2/9] drm: hold master_lookup_lock when releasing a drm_file's master Desmond Cheong Zhi Xi
2021-08-18 10:05 ` Daniel Vetter [this message]
2021-08-18 14:50 ` Desmond Cheong Zhi Xi
2021-08-18 7:38 ` [PATCH v3 3/9] drm: check for null master in drm_is_current_master_locked Desmond Cheong Zhi Xi
2021-08-18 10:04 ` Daniel Vetter
2021-08-18 7:38 ` [PATCH v3 4/9] drm: fix potential null ptr dereferences in drm_{auth,ioctl} Desmond Cheong Zhi Xi
2021-08-18 10:11 ` Daniel Vetter
2021-08-18 15:37 ` Desmond Cheong Zhi Xi
2021-08-18 16:33 ` [Intel-gfx] [PATCH v3 4/9] drm: fix potential null ptr dereferences in drm_{auth, ioctl} Daniel Vetter
2021-08-19 5:31 ` Desmond Cheong Zhi Xi
2021-08-18 7:38 ` [PATCH v3 5/9] drm: protect magic_map,unique{_len} with master_lookup_lock Desmond Cheong Zhi Xi
2021-08-18 10:43 ` Daniel Vetter
2021-08-18 7:38 ` [PATCH v3 6/9] drm: convert drm_device.master_mutex into a rwsem Desmond Cheong Zhi Xi
2021-08-18 7:38 ` [PATCH v3 7/9] drm: update global mutex lock in the ioctl handler Desmond Cheong Zhi Xi
2021-08-18 11:02 ` Daniel Vetter
2021-08-19 10:52 ` Desmond Cheong Zhi Xi
2021-08-19 11:21 ` [Intel-gfx] " Daniel Vetter
2021-08-18 7:38 ` [PATCH v3 8/9] kernel: export task_work_add Desmond Cheong Zhi Xi
2021-08-18 11:06 ` Daniel Vetter
2021-08-19 9:26 ` Christoph Hellwig
2021-08-19 9:40 ` Desmond Cheong Zhi Xi
2021-08-18 7:38 ` [PATCH v3 9/9] drm: avoid races with modesetting rights Desmond Cheong Zhi Xi
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