diff options
| author | Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> | 2021-07-12 12:35:07 +0800 |
|---|---|---|
| committer | Daniel Vetter <daniel.vetter@ffwll.ch> | 2021-07-20 20:17:58 +0200 |
| commit | 0b0860a3cf5eccf183760b1177a1dcdb821b0b66 (patch) | |
| tree | d8893b9878ac83636e71fc5113443a8219d4968a /drivers/gpu/drm/drm_auth.c | |
| parent | 1f7ef07cfa14fb8557d1f1b7a14c76926142a4fb (diff) | |
drm: serialize drm_file.master with a new spinlock
Currently, drm_file.master pointers should be protected by
drm_device.master_mutex when being dereferenced. This is because
drm_file.master is not invariant for the lifetime of drm_file. If
drm_file is not the creator of master, then drm_file.is_master is
false, and a call to drm_setmaster_ioctl will invoke
drm_new_set_master, which then allocates a new master for drm_file and
puts the old master.
Thus, without holding drm_device.master_mutex, the old value of
drm_file.master could be freed while it is being used by another
concurrent process.
However, it is not always possible to lock drm_device.master_mutex to
dereference drm_file.master. Through the fbdev emulation code, this
might occur in a deep nest of other locks. But drm_device.master_mutex
is also the outermost lock in the nesting hierarchy, so this leads to
potential deadlocks.
To address this, we introduce a new spin lock at the bottom of the
lock hierarchy that only serializes drm_file.master. With this change,
the value of drm_file.master changes only when both
drm_device.master_mutex and drm_file.master_lookup_lock are
held. Hence, any process holding either of those locks can ensure that
the value of drm_file.master will not change concurrently.
Since no lock depends on the new drm_file.master_lookup_lock, when
drm_file.master is dereferenced, but drm_device.master_mutex cannot be
held, we can safely protect the master pointer with
drm_file.master_lookup_lock.
Reported-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210712043508.11584-5-desmondcheongzx@gmail.com
Diffstat (limited to 'drivers/gpu/drm/drm_auth.c')
| -rw-r--r-- | drivers/gpu/drm/drm_auth.c | 17 |
1 files changed, 11 insertions, 6 deletions
diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c index ab1863c5a5a0..30a239901b36 100644 --- a/drivers/gpu/drm/drm_auth.c +++ b/drivers/gpu/drm/drm_auth.c @@ -164,16 +164,18 @@ static void drm_set_master(struct drm_device *dev, struct drm_file *fpriv, static int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv) { struct drm_master *old_master; + struct drm_master *new_master; lockdep_assert_held_once(&dev->master_mutex); WARN_ON(fpriv->is_master); old_master = fpriv->master; - fpriv->master = drm_master_create(dev); - if (!fpriv->master) { - fpriv->master = old_master; + new_master = drm_master_create(dev); + if (!new_master) return -ENOMEM; - } + spin_lock(&fpriv->master_lookup_lock); + fpriv->master = new_master; + spin_unlock(&fpriv->master_lookup_lock); fpriv->is_master = 1; fpriv->authenticated = 1; @@ -332,10 +334,13 @@ int drm_master_open(struct drm_file *file_priv) * any master object for render clients */ mutex_lock(&dev->master_mutex); - if (!dev->master) + if (!dev->master) { ret = drm_new_set_master(dev, file_priv); - else + } else { + spin_lock(&file_priv->master_lookup_lock); file_priv->master = drm_master_get(dev->master); + spin_unlock(&file_priv->master_lookup_lock); + } mutex_unlock(&dev->master_mutex); return ret; |