On Thu, Jul 13, 2017 at 03:04:58PM +0100, Chris Wilson wrote:
> Quoting Jiri Slaby (2017-07-13 14:57:31)
> > Stealing this thread as an opensuse user hit that too:
> > https://bugzilla.suse.com/show_bug.cgi?id=1045105
>
> It's a false positive. I did once upon a time send some patches to move
> the lockdep warning to kref so that didn't need to call it from drm
> before an unlocked path. Basically you want
>
> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> index 8dc11064253d..3118aed844f1 100644
> --- a/drivers/gpu/drm/drm_gem.c
> +++ b/drivers/gpu/drm/drm_gem.c
> @@ -826,7 +826,6 @@ drm_gem_object_put_unlocked(struct drm_gem_object *obj)
> return;
>
> dev = obj->dev;
> - might_lock(&dev->struct_mutex);
>
> if (dev->driver->gem_free_object_unlocked)
> kref_put(&obj->refcount, drm_gem_object_free);
> diff --git a/include/linux/kref.h b/include/linux/kref.h
> index 29220724bf1c..4b1133cd5d20 100644
> --- a/include/linux/kref.h
> +++ b/include/linux/kref.h
> @@ -77,6 +77,8 @@ static inline int kref_put_mutex(struct kref *kref,
> void (*release)(struct kref *kref),
> struct mutex *lock)
> {
> + might_lock(lock);
> +
> if (refcount_dec_and_mutex_lock(&kref->refcount, lock)) {
> release(kref);
> return 1;
>
>
> Though now we probably want to move that might_lock() into refcount.
I think we want this here:
diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index 8dc11064253d..9663a79dd363 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -826,13 +826,15 @@ drm_gem_object_put_unlocked(struct drm_gem_object *obj)
return;
dev = obj->dev;
- might_lock(&dev->struct_mutex);
if (dev->driver->gem_free_object_unlocked)
kref_put(&obj->refcount, drm_gem_object_free);
- else if (kref_put_mutex(&obj->refcount, drm_gem_object_free,
+ else {
+ might_lock(&dev->struct_mutex);
+ if (kref_put_mutex(&obj->refcount, drm_gem_object_free,
&dev->struct_mutex))
- mutex_unlock(&dev->struct_mutex);
+ mutex_unlock(&dev->struct_mutex);
+ }
}
EXPORT_SYMBOL(drm_gem_object_put_unlocked);
If it works I'll wrap it into a patch. Note you need rather new-ish kernel
to make sure we're sufficiently struct_mutex free in i915 (otherwise
there's still the locking loop). v4.10 should be new enough afaics.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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