Re: [PATCH v3 2/9] drm: hold master_lookup_lock when releasing a drm_file's master
From: Daniel Vetter <hidden>
Date: 2021-08-18 10:05:31
Also in:
dri-devel, intel-gfx, linux-kernel-mentees, lkml
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 <redacted>
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
quoted hunk ↗ jump to hunk
--- 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