The DRM core depends on mm->mmap_sem being the outer lock in order to setup/teardown and utilize fault handlers. If we taint the mm->mmap_sem as soon as we open the device for a process, we can define this proper ordering for lockdep and so it will report any violations early.
Signed-off-by: Chris Wilson chris@chris-wilson.co.uk --- drivers/gpu/drm/drm_fops.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c index aeef58ed359b..a95d588c24c8 100644 --- a/drivers/gpu/drm/drm_fops.c +++ b/drivers/gpu/drm/drm_fops.c @@ -246,6 +246,19 @@ static int drm_open_helper(struct file *filp, struct drm_minor *minor)
DRM_DEBUG("pid = %d, minor = %d\n", task_pid_nr(current), minor->index);
+ if (IS_ENABLED(CONFIG_LOCKDEP)) { + /* We depend upon the strict order of mmap_sem outside of + * struct_mutex in order for the fault handlers and their + * setup/teardown. Taint mmap_sem as early as possible in + * order to define the proper order and flag ABBA errors + * should the order ever be inverted. + */ + down_write(¤t->mm->mmap_sem); + mutex_lock(&dev->struct_mutex); + mutex_unlock(&dev->struct_mutex); + up_write(¤t->mm->mmap_sem); + } + priv = kzalloc(sizeof(*priv), GFP_KERNEL); if (!priv) return -ENOMEM;