All drivers will be moved to get/put pages explicitly and then the last
put_pages() will be invoked during gem_free() time by some drivers.
We can't touch reservation lock when GEM is freed because that will cause
a spurious warning from lockdep when shrinker support will be added.
Lockdep doesn't know that fs_reclaim isn't functioning for a freed object,
and thus, can't deadlock. Release pages directly without taking reservation
lock if GEM is freed and its refcount is zero.
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>
---
drivers/gpu/drm/drm_gem_shmem_helper.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index f5ed64f78648..c7357110ca76 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -242,6 +242,22 @@ void drm_gem_shmem_put_pages(struct drm_gem_shmem_object *shmem)
if (refcount_dec_not_one(&shmem->pages_use_count))
return;
+ /*
+ * Destroying the object is a special case because acquiring
+ * the obj lock can cause a locking order inversion between
+ * reservation_ww_class_mutex and fs_reclaim.
+ *
+ * This deadlock is not actually possible, because no one should
+ * be already holding the lock when GEM is released. Unfortunately
+ * lockdep is not aware of this detail. So when the refcount drops
+ * to zero, we pretend it is already locked.
+ */
+ if (!kref_read(&shmem->base.refcount)) {
+ if (refcount_dec_and_test(&shmem->pages_use_count))
+ drm_gem_shmem_free_pages(shmem);
+ return;
+ }
+
dma_resv_lock(shmem->base.resv, NULL);
drm_gem_shmem_put_pages_locked(shmem);
dma_resv_unlock(shmem->base.resv);
--
2.43.0
