drm: Hold the mutex when dropping the last GEM reference (v2)
In order to be fully threadsafe we need to check that the drm_gem_object refcount is still 0 after acquiring the mutex in order to call the free function. Otherwise, we may encounter scenarios like: Thread A: Thread B: drm_gem_close unreference_unlocked kref_put mutex_lock ... i915_gem_evict ... kref_get -> BUG ... i915_gem_unbind ... kref_put ... i915_gem_object_free ... mutex_unlock mutex_lock i915_gem_object_free -> BUG i915_gem_object_unbind kfree mutex_unlock Note that no driver is currently using the free_unlocked vfunc and it is scheduled for removal, hasten that process. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=30454 Reported-and-Tested-by: Magnus Kessler <Magnus.Kessler@gmx.net> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: stable@kernel.org Signed-off-by: Dave Airlie <airlied@redhat.com>
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@ -462,28 +462,6 @@ drm_gem_object_free(struct kref *kref)
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}
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EXPORT_SYMBOL(drm_gem_object_free);
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/**
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* Called after the last reference to the object has been lost.
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* Must be called without holding struct_mutex
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*
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* Frees the object
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*/
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void
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drm_gem_object_free_unlocked(struct kref *kref)
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{
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struct drm_gem_object *obj = (struct drm_gem_object *) kref;
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struct drm_device *dev = obj->dev;
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if (dev->driver->gem_free_object_unlocked != NULL)
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dev->driver->gem_free_object_unlocked(obj);
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else if (dev->driver->gem_free_object != NULL) {
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mutex_lock(&dev->struct_mutex);
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dev->driver->gem_free_object(obj);
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mutex_unlock(&dev->struct_mutex);
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}
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}
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EXPORT_SYMBOL(drm_gem_object_free_unlocked);
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static void drm_gem_object_ref_bug(struct kref *list_kref)
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{
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BUG();
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@ -808,7 +808,6 @@ struct drm_driver {
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*/
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int (*gem_init_object) (struct drm_gem_object *obj);
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void (*gem_free_object) (struct drm_gem_object *obj);
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void (*gem_free_object_unlocked) (struct drm_gem_object *obj);
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/* vga arb irq handler */
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void (*vgaarb_irq)(struct drm_device *dev, bool state);
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@ -1456,7 +1455,6 @@ int drm_gem_init(struct drm_device *dev);
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void drm_gem_destroy(struct drm_device *dev);
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void drm_gem_object_release(struct drm_gem_object *obj);
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void drm_gem_object_free(struct kref *kref);
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void drm_gem_object_free_unlocked(struct kref *kref);
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struct drm_gem_object *drm_gem_object_alloc(struct drm_device *dev,
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size_t size);
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int drm_gem_object_init(struct drm_device *dev,
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@ -1484,8 +1482,12 @@ drm_gem_object_unreference(struct drm_gem_object *obj)
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static inline void
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drm_gem_object_unreference_unlocked(struct drm_gem_object *obj)
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{
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if (obj != NULL)
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kref_put(&obj->refcount, drm_gem_object_free_unlocked);
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if (obj != NULL) {
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struct drm_device *dev = obj->dev;
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mutex_lock(&dev->struct_mutex);
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kref_put(&obj->refcount, drm_gem_object_free);
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mutex_unlock(&dev->struct_mutex);
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}
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}
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int drm_gem_handle_create(struct drm_file *file_priv,
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