dma-fence: Serialise signal enabling (dma_fence_enable_sw_signaling)

Make dma_fence_enable_sw_signaling() behave like its
dma_fence_add_callback() and dma_fence_default_wait() counterparts and
perform the test to enable signaling under the fence->lock, along with
the action to do so. This ensure that should an implementation be trying
to flush the cb_list (by signaling) on retirement before freeing the
fence, it can do so in a race-free manner.

See also 0fc89b6802ba ("dma-fence: Simply wrap dma_fence_signal_locked
with dma_fence_signal").

v2: Refactor all 3 enable_signaling paths to use a common function.
v3: Don't argue, just keep the tracepoint in the existing spot.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191004101140.32713-1-chris@chris-wilson.co.uk

diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
index 2c136ae..052a41e 100644 (file)
--- a/drivers/dma-buf/dma-fence.c
+++ b/drivers/dma-buf/dma-fence.c
@@ -273,6 +273,30 @@ void dma_fence_free(struct dma_fence *fence)
 }
 EXPORT_SYMBOL(dma_fence_free);
 
+static bool __dma_fence_enable_signaling(struct dma_fence *fence)
+{
+       bool was_set;
+
+       lockdep_assert_held(fence->lock);
+
+       was_set = test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
+                                  &fence->flags);
+
+       if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
+               return false;
+
+       if (!was_set && fence->ops->enable_signaling) {
+               trace_dma_fence_enable_signal(fence);
+
+               if (!fence->ops->enable_signaling(fence)) {
+                       dma_fence_signal_locked(fence);
+                       return false;
+               }
+       }
+
+       return true;
+}
+
 /**
  * dma_fence_enable_sw_signaling - enable signaling on fence
  * @fence: the fence to enable
@@ -285,19 +309,12 @@ void dma_fence_enable_sw_signaling(struct dma_fence *fence)
 {
        unsigned long flags;
 
-       if (!test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
-                             &fence->flags) &&
-           !test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags) &&
-           fence->ops->enable_signaling) {
-               trace_dma_fence_enable_signal(fence);
-
-               spin_lock_irqsave(fence->lock, flags);
-
-               if (!fence->ops->enable_signaling(fence))
-                       dma_fence_signal_locked(fence);
+       if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
+               return;
 
-               spin_unlock_irqrestore(fence->lock, flags);
-       }
+       spin_lock_irqsave(fence->lock, flags);
+       __dma_fence_enable_signaling(fence);
+       spin_unlock_irqrestore(fence->lock, flags);
 }
 EXPORT_SYMBOL(dma_fence_enable_sw_signaling);
 
@@ -331,7 +348,6 @@ int dma_fence_add_callback(struct dma_fence *fence, struct dma_fence_cb *cb,
 {
        unsigned long flags;
        int ret = 0;
-       bool was_set;
 
        if (WARN_ON(!fence || !func))
                return -EINVAL;
@@ -343,25 +359,14 @@ int dma_fence_add_callback(struct dma_fence *fence, struct dma_fence_cb *cb,
 
        spin_lock_irqsave(fence->lock, flags);
 
-       was_set = test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
-                                  &fence->flags);
-
-       if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
-               ret = -ENOENT;
-       else if (!was_set && fence->ops->enable_signaling) {
-               trace_dma_fence_enable_signal(fence);
-
-               if (!fence->ops->enable_signaling(fence)) {
-                       dma_fence_signal_locked(fence);
-                       ret = -ENOENT;
-               }
-       }
-
-       if (!ret) {
+       if (__dma_fence_enable_signaling(fence)) {
                cb->func = func;
                list_add_tail(&cb->node, &fence->cb_list);
-       } else
+       } else {
                INIT_LIST_HEAD(&cb->node);
+               ret = -ENOENT;
+       }
+
        spin_unlock_irqrestore(fence->lock, flags);
 
        return ret;
@@ -461,7 +466,6 @@ dma_fence_default_wait(struct dma_fence *fence, bool intr, signed long timeout)
        struct default_wait_cb cb;
        unsigned long flags;
        signed long ret = timeout ? timeout : 1;
-       bool was_set;
 
        if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
                return ret;
@@ -473,21 +477,9 @@ dma_fence_default_wait(struct dma_fence *fence, bool intr, signed long timeout)
                goto out;
        }
 
-       was_set = test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
-                                  &fence->flags);
-
-       if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
+       if (!__dma_fence_enable_signaling(fence))
                goto out;
 
-       if (!was_set && fence->ops->enable_signaling) {
-               trace_dma_fence_enable_signal(fence);
-
-               if (!fence->ops->enable_signaling(fence)) {
-                       dma_fence_signal_locked(fence);
-                       goto out;
-               }
-       }
-
        if (!timeout) {
                ret = 0;
                goto out;