| Message ID | 20210818073824.1560124-3-desmondcheongzx@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm, kernel: update locking for DRM | expand |
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 >
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@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 > 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 >> >
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); }
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> --- drivers/gpu/drm/drm_auth.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)