drm/msm: Protect obj->active_count under obj lock

Previously we only held obj lock in the _active_get() path, and relied
on atomic_dec_return() to not be racy in the _active_put() path where
obj lock was not held.

But this is a false sense of security.  Unlike obj lifetime refcnt,
where you do not expect to *increase* the refcnt after the last put
(which would mean that something has gone horribly wrong with the
object liveness reference counting), the active_count can increase
again from zero.  Racing _active_put()s and _active_get()s could leave
the obj on the wrong mm list.

But in the retire path, immediately after the _active_put(), the
_unpin_iova() would acquire obj lock.  So just move the locking earlier
and rely on that to protect obj->active_count.

Fixes: c5c1643cef7a ("drm/msm: Drop struct_mutex from the retire path")
Signed-off-by: Rob Clark <robdclark@chromium.org>

diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
index 0319e0ad07f5b0b564ce957c7fe1c5963c08b9af..562db92aa631d97f65f928306239ce45534421f7 100644 (file)
--- a/drivers/gpu/drm/msm/msm_gem.c
+++ b/drivers/gpu/drm/msm/msm_gem.c
@@ -769,7 +769,7 @@ void msm_gem_active_get(struct drm_gem_object *obj, struct msm_gpu *gpu)
        WARN_ON(!msm_gem_is_locked(obj));
        WARN_ON(msm_obj->madv != MSM_MADV_WILLNEED);
 
-       if (!atomic_fetch_inc(&msm_obj->active_count)) {
+       if (msm_obj->active_count++ == 0) {
                mutex_lock(&priv->mm_lock);
                list_del_init(&msm_obj->mm_list);
                list_add_tail(&msm_obj->mm_list, &gpu->active_list);
@@ -783,8 +783,9 @@ void msm_gem_active_put(struct drm_gem_object *obj)
        struct msm_drm_private *priv = obj->dev->dev_private;
 
        might_sleep();
+       WARN_ON(!msm_gem_is_locked(obj));
 
-       if (!atomic_dec_return(&msm_obj->active_count)) {
+       if (--msm_obj->active_count == 0) {
                mutex_lock(&priv->mm_lock);
                list_del_init(&msm_obj->mm_list);
                list_add_tail(&msm_obj->mm_list, &priv->inactive_list);
@@ -935,15 +936,15 @@ void msm_gem_free_object(struct drm_gem_object *obj)
        struct drm_device *dev = obj->dev;
        struct msm_drm_private *priv = dev->dev_private;
 
-       /* object should not be on active list: */
-       WARN_ON(is_active(msm_obj));
-
        mutex_lock(&priv->mm_lock);
        list_del(&msm_obj->mm_list);
        mutex_unlock(&priv->mm_lock);
 
        msm_gem_lock(obj);
 
+       /* object should not be on active list: */
+       WARN_ON(is_active(msm_obj));
+
        put_iova(obj);
 
        if (obj->import_attach) {

diff --git a/drivers/gpu/drm/msm/msm_gem.h b/drivers/gpu/drm/msm/msm_gem.h
index d79e7019cc885e2a1909f1f61b4d8910c72c0a3d..3355a48a023bd41797be24ff047b57d86450e6c5 100644 (file)
--- a/drivers/gpu/drm/msm/msm_gem.h
+++ b/drivers/gpu/drm/msm/msm_gem.h
@@ -87,7 +87,7 @@ struct msm_gem_object {
 
        char name[32]; /* Identifier to print for the debugfs files */
 
-       atomic_t active_count;
+       int active_count;
 };
 #define to_msm_bo(x) container_of(x, struct msm_gem_object, base)
 
@@ -185,7 +185,8 @@ msm_gem_is_locked(struct drm_gem_object *obj)
 
 static inline bool is_active(struct msm_gem_object *msm_obj)
 {
-       return atomic_read(&msm_obj->active_count);
+       WARN_ON(!msm_gem_is_locked(&msm_obj->base));
+       return msm_obj->active_count;
 }
 
 static inline bool is_purgeable(struct msm_gem_object *msm_obj)

diff --git a/drivers/gpu/drm/msm/msm_gpu.c b/drivers/gpu/drm/msm/msm_gpu.c
index dfa3b5ad2099c59d25a128c65720e4661d2a4034..ab7c167b062362a69c93286daa8bf05b617741ee 100644 (file)
--- a/drivers/gpu/drm/msm/msm_gpu.c
+++ b/drivers/gpu/drm/msm/msm_gpu.c
@@ -719,11 +719,13 @@ static void retire_submit(struct msm_gpu *gpu, struct msm_ringbuffer *ring,
                stats->alwayson_start, stats->alwayson_end);
 
        for (i = 0; i < submit->nr_bos; i++) {
-               struct msm_gem_object *msm_obj = submit->bos[i].obj;
+               struct drm_gem_object *obj = &submit->bos[i].obj->base;
 
-               msm_gem_active_put(&msm_obj->base);
-               msm_gem_unpin_iova(&msm_obj->base, submit->aspace);
-               drm_gem_object_put(&msm_obj->base);
+               msm_gem_lock(obj);
+               msm_gem_active_put(obj);
+               msm_gem_unpin_iova_locked(obj, submit->aspace);
+               msm_gem_unlock(obj);
+               drm_gem_object_put(obj);
        }
 
        pm_runtime_mark_last_busy(&gpu->pdev->dev);