On 18/8/21 6:05 pm, Daniel Vetter wrote:
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@xxxxxxxxx>
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
Ah ok got it, I didn't realize that. I'll drop patch 2 and 3 from the
series then.
---
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
