Re: [PATCH 05/19] dma-buf/selftests: test RCU ops and inline lock

[Tvrtko Ursulin]

On 11/12/2025 13:16, Christian König wrote:
Drop the mock_fence and the kmem_cache, instead use the inline lock and
test if the ops are properly dropped after signaling.

Signed-off-by: Christian König <christian.koe...@amd.com>
---
  drivers/dma-buf/st-dma-fence.c | 44 ++++++++--------------------------
  1 file changed, 10 insertions(+), 34 deletions(-)

diff --git a/drivers/dma-buf/st-dma-fence.c b/drivers/dma-buf/st-dma-fence.c
index 5d0d9abc6e21..65221270fd06 100644
--- a/drivers/dma-buf/st-dma-fence.c
+++ b/drivers/dma-buf/st-dma-fence.c
@@ -14,43 +14,26 @@
  
  #include "selftest.h"
  
-static struct kmem_cache *slab_fences;
-
-static struct mock_fence {
-       struct dma_fence base;
-       struct spinlock lock;
-} *to_mock_fence(struct dma_fence *f) {
-       return container_of(f, struct mock_fence, base);
-}
-
  static const char *mock_name(struct dma_fence *f)
  {
        return "mock";
  }
  
-static void mock_fence_release(struct dma_fence *f)
-{
-       kmem_cache_free(slab_fences, to_mock_fence(f));
-}
-
  static const struct dma_fence_ops mock_ops = {
        .get_driver_name = mock_name,
        .get_timeline_name = mock_name,
-       .release = mock_fence_release,
  };
  
  static struct dma_fence *mock_fence(void)
  {
-       struct mock_fence *f;
+       struct dma_fence *f;
  
-	f = kmem_cache_alloc(slab_fences, GFP_KERNEL);
+       f = kmalloc(sizeof(*f), GFP_KERNEL);
        if (!f)
                return NULL;
  
-	spin_lock_init(&f->lock);
-       dma_fence_init(&f->base, &mock_ops, &f->lock, 0, 0);
-
-       return &f->base;
+       dma_fence_init(f, &mock_ops, NULL, 0, 0);
+       return f;
  }
  
  static int sanitycheck(void *arg)
@@ -90,6 +73,11 @@ static int test_signaling(void *arg)
                goto err_free;
        }
  
+	if (rcu_dereference_protected(f->ops, true)) {
+               pr_err("Fence ops not cleared on signal\n");
+               goto err_free;
+       }

Bump to after the signaled check just below? Otherwise the signaled 
state hasn't been ascertained yet.
+
        if (!dma_fence_is_signaled(f)) {
                pr_err("Fence not reporting signaled\n");
                goto err_free;
@@ -540,19 +528,7 @@ int dma_fence(void)
                SUBTEST(test_stub),
                SUBTEST(race_signal_callback),
        };
-       int ret;
  
  	pr_info("sizeof(dma_fence)=%zu\n", sizeof(struct dma_fence));
-
-       slab_fences = KMEM_CACHE(mock_fence,
-                                SLAB_TYPESAFE_BY_RCU |

Hm.. race_signal_callback looks like it could be depending on 
SLAB_TYPESAFE_BY_RCU. To you not?

Regards,

Tvrtko

-                                SLAB_HWCACHE_ALIGN);
-       if (!slab_fences)
-               return -ENOMEM;
-
-       ret = subtests(tests, NULL);
-
-       kmem_cache_destroy(slab_fences);
-
-       return ret;
+       return subtests(tests, NULL);
  }