Re: [PATCH] drm/syncobj: Avoid kmalloc(GFP_KERNEL) under spinlock

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Am 25.10.18 um 17:08 schrieb Chunming Zhou:
drivers/gpu/drm/drm_syncobj.c:202:4-14: ERROR: function drm_syncobj_find_signal_pt_for_point called on line 390 inside lock on line 389 but uses GFP_KERNEL

   Find functions that refer to GFP_KERNEL but are called with locks held.

Generated by: scripts/coccinelle/locks/call_kern.cocci

v2:
syncobj->timeline still needs protect.

v3:
use a global signaled fence instead of re-allocation.

v4:
Don't need moving lock.
Don't expose func.

Tested by: syncobj_wait and ./deqp-vk -n dEQP-VK.*semaphore* with
lock debug kernel options enabled.

Signed-off-by: Chunming Zhou <david1.zhou@xxxxxxx>
Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Cc: intel-gfx@xxxxxxxxxxxxxxxxxxxxx
Cc: Christian König <easy2remember.chk@xxxxxxxxxxxxxx>
Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
CC: Julia Lawall <julia.lawall@xxxxxxx>
---
  drivers/gpu/drm/drm_syncobj.c | 41 ++++++++++++++++++++---------------
  1 file changed, 24 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
index b7eaa603f368..fab0a2cf672e 100644
--- a/drivers/gpu/drm/drm_syncobj.c
+++ b/drivers/gpu/drm/drm_syncobj.c
@@ -80,6 +80,23 @@ struct drm_syncobj_signal_pt {
  	struct list_head list;
  };
+static DEFINE_SPINLOCK(signaled_fence_lock);
+static struct dma_fence signaled_fence;
+
+static struct dma_fence *drm_syncobj_signaled_fence_get(void)

Maybe name that drm_syncobj_get_stub_fence().

+{
+	spin_lock(&signaled_fence_lock);
+	if (!signaled_fence.ops) {
+		dma_fence_init(&signaled_fence,
+			       &drm_syncobj_stub_fence_ops,
+			       &signaled_fence_lock,
+			       0, 0);
+		dma_fence_signal_locked(&signaled_fence);
+	}
+	spin_unlock(&signaled_fence_lock);
+
+	return dma_fence_get(&signaled_fence);
+}
  /**
   * drm_syncobj_find - lookup and reference a sync object.
   * @file_private: drm file private pointer
@@ -111,24 +128,12 @@ static struct dma_fence
  				      uint64_t point)
  {
  	struct drm_syncobj_signal_pt *signal_pt;
+	struct dma_fence *f = NULL;
if ((syncobj->type == DRM_SYNCOBJ_TYPE_TIMELINE) &&
  	    (point <= syncobj->timeline)) {
-		struct drm_syncobj_stub_fence *fence =
-			kzalloc(sizeof(struct drm_syncobj_stub_fence),
-				GFP_KERNEL);
-
-		if (!fence)
-			return NULL;
-		spin_lock_init(&fence->lock);
-		dma_fence_init(&fence->base,
-			       &drm_syncobj_stub_fence_ops,
-			       &fence->lock,
-			       syncobj->timeline_context,
-			       point);
-
-		dma_fence_signal(&fence->base);
-		return &fence->base;
+		f = drm_syncobj_signaled_fence_get();
+		goto out;
  	}
list_for_each_entry(signal_pt, &syncobj->signal_pt_list, list) {
@@ -137,9 +142,11 @@ static struct dma_fence
  		if ((syncobj->type == DRM_SYNCOBJ_TYPE_BINARY) &&
  		    (point != signal_pt->value))
  			continue;
-		return dma_fence_get(&signal_pt->fence_array->base);
+		f = dma_fence_get(&signal_pt->fence_array->base);
+		goto out;
  	}
-	return NULL;
+out:
+	return f;

I think we can drop this change now and just return directly.

Christian.

  }
static void drm_syncobj_add_callback_locked(struct drm_syncobj *syncobj,

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