[PATCH v2 2/2] dma-buf: Assign separate lockdep class to array lock

[Matthew Brost <matthew.brost@intel.com>]

dma_fence_array_enable_signaling() runs while holding the array
inline_lock and may add callbacks to underlying fences, which takes
their inline_lock.

Since both locks share the same lockdep class, this valid nesting
triggers a recursive locking warning. Assign a distinct lockdep class
to the array inline_lock so lockdep can correctly model the hierarchy.

Fixes: 5943243914b9 ("dma-buf: use inline lock for the dma-fence-array")
Cc: Christian König <christian.koenig@amd.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Cc: Philipp Stanner <phasta@kernel.org>
Cc: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>

---
v2:
 - Drop if IS_ENABLED(CONFIG_LOCKDEP), lockdep does this
---
 drivers/dma-buf/dma-fence-array.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/dma-buf/dma-fence-array.c b/drivers/dma-buf/dma-fence-array.c
index cd970eceaefb..089f69469524 100644
--- a/drivers/dma-buf/dma-fence-array.c
+++ b/drivers/dma-buf/dma-fence-array.c
@@ -200,6 +200,8 @@ void dma_fence_array_init(struct dma_fence_array *array,
 			  u64 context, unsigned seqno,
 			  bool signal_on_any)
 {
+	static struct lock_class_key dma_fence_array_lock_key;
+
 	WARN_ON(!num_fences || !fences);
 
 	array->num_fences = num_fences;
@@ -208,6 +210,18 @@ void dma_fence_array_init(struct dma_fence_array *array,
 		       seqno);
 	init_irq_work(&array->work, irq_dma_fence_array_work);
 
+	/*
+	 * dma_fence_array_enable_signaling() is invoked while holding
+	 * array->base.inline_lock and may call dma_fence_add_callback()
+	 * on the underlying fences, which takes their inline_lock.
+	 *
+	 * Since both locks share the same lockdep class, this legitimate
+	 * nesting confuses lockdep and triggers a recursive locking
+	 * warning. Assign a separate lockdep class to the array lock
+	 * to model this hierarchy correctly.
+	 */
+	lockdep_set_class(&array->base.inline_lock, &dma_fence_array_lock_key);
+
 	atomic_set(&array->num_pending, signal_on_any ? 1 : num_fences);
 	array->fences = fences;
 
-- 
2.34.1