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drm: Hold the mutex when dropping the last GEM reference (v2)

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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>
This commit is contained in:
Chris Wilson 2010-09-30 09:10:26 +01:00 committed by Dave Airlie
parent 29d08b3efd
commit 39b4d07aa3
2 changed files with 6 additions and 26 deletions
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22
drivers/gpu/drm/drm_gem.c
View file

@ -462,28 +462,6 @@ drm_gem_object_free(struct kref *kref)
}
EXPORT_SYMBOL(drm_gem_object_free);
/**
* Called after the last reference to the object has been lost.
* Must be called without holding struct_mutex
*
* Frees the object
*/
void
drm_gem_object_free_unlocked(struct kref *kref)
{
struct drm_gem_object *obj = (struct drm_gem_object *) kref;
struct drm_device *dev = obj->dev;
if (dev->driver->gem_free_object_unlocked != NULL)
dev->driver->gem_free_object_unlocked(obj);
else if (dev->driver->gem_free_object != NULL) {
mutex_lock(&dev->struct_mutex);
dev->driver->gem_free_object(obj);
mutex_unlock(&dev->struct_mutex);
}
}
EXPORT_SYMBOL(drm_gem_object_free_unlocked);
static void drm_gem_object_ref_bug(struct kref *list_kref)
{
BUG();

10
include/drm/drmP.h
View file

@ -808,7 +808,6 @@ struct drm_driver {
*/
int (*gem_init_object) (struct drm_gem_object *obj);
void (*gem_free_object) (struct drm_gem_object *obj);
void (*gem_free_object_unlocked) (struct drm_gem_object *obj);
/* vga arb irq handler */
void (*vgaarb_irq)(struct drm_device *dev, bool state);
@ -1456,7 +1455,6 @@ int drm_gem_init(struct drm_device *dev);
void drm_gem_destroy(struct drm_device *dev);
void drm_gem_object_release(struct drm_gem_object *obj);
void drm_gem_object_free(struct kref *kref);
void drm_gem_object_free_unlocked(struct kref *kref);
struct drm_gem_object *drm_gem_object_alloc(struct drm_device *dev,
size_t size);
int drm_gem_object_init(struct drm_device *dev,
@ -1484,8 +1482,12 @@ drm_gem_object_unreference(struct drm_gem_object *obj)
static inline void
drm_gem_object_unreference_unlocked(struct drm_gem_object *obj)
{
if (obj != NULL)
kref_put(&obj->refcount, drm_gem_object_free_unlocked);
if (obj != NULL) {
struct drm_device *dev = obj->dev;
mutex_lock(&dev->struct_mutex);
kref_put(&obj->refcount, drm_gem_object_free);
mutex_unlock(&dev->struct_mutex);
}
}
int drm_gem_handle_create(struct drm_file *file_priv,