In a future patch, a read lock on drm_device.master_rwsem is
held in the ioctl handler before the check for ioctl
permissions. However, this inverts the lock hierarchy of
drm_global_mutex --> master_rwsem.
To avoid this, we do some prep work to grab the drm_global_mutex
before checking for ioctl permissions.
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@xxxxxxxxx>
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
---
drivers/gpu/drm/drm_ioctl.c | 21 ++++++++++++---------
1 file changed, 12 insertions(+), 9 deletions(-)
diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index d25713b09b80..59c5aa850dd5 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -767,24 +767,27 @@ long drm_ioctl_kernel(struct file *file, drm_ioctl_t *func, void *kdata,
{
struct drm_file *file_priv = file->private_data;
struct drm_device *dev = file_priv->minor->dev;
+ bool locked_ioctl;
int retcode;
if (drm_dev_is_unplugged(dev))
return -ENODEV;
+ /* Enforce sane locking for modern driver ioctls. */
+ locked_ioctl = (unlikely(drm_core_check_feature(dev, DRIVER_LEGACY)) &&
+ !(flags & DRM_UNLOCKED));
+ if (locked_ioctl)
+ mutex_lock(&drm_global_mutex);
+
retcode = drm_ioctl_permit(flags, file_priv);
if (unlikely(retcode))
- return retcode;
+ goto out;
- /* Enforce sane locking for modern driver ioctls. */
- if (likely(!drm_core_check_feature(dev, DRIVER_LEGACY)) ||
- (flags & DRM_UNLOCKED))
- retcode = func(dev, kdata, file_priv);
- else {
- mutex_lock(&drm_global_mutex);
- retcode = func(dev, kdata, file_priv);
+ retcode = func(dev, kdata, file_priv);
+
+out:
+ if (locked_ioctl)
mutex_unlock(&drm_global_mutex);
- }
return retcode;
}
EXPORT_SYMBOL(drm_ioctl_kernel);
--
2.25.1
