Locking question for DRM

[Alan Cox]

Various bits of the DRM deal with minor->master:

In the case of the open helper its protected by the struct mutex.

In the release path it's protected on some paths, but not this one ...

     /* if the master has gone away we can't do anything with the lock */
        if (file_priv->minor->master)
                drm_master_release(dev, filp);

and I can't see what makes this safe if the drm_release for the master
and a client occur at the same time ?

The setmaster/dropmaster ioctl seems similar - the various conditional
checks are not protected from parallel changes occuring during their
execution.

Is this a bug or is something clever afoot ?

Alan