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Subject[PATCH 4.19 003/245] dma-fence: Serialise signal enabling (dma_fence_enable_sw_signaling)
Date
From: Chris Wilson <chris@chris-wilson.co.uk>

[ Upstream commit 9c98f021e4e717ffd9948fa65340ea3ef12b7935 ]

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
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/dma-buf/dma-fence.c | 78 +++++++++++++++++--------------------
1 file changed, 35 insertions(+), 43 deletions(-)

diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
index 1551ca7df3941..8586cc05def17 100644
--- a/drivers/dma-buf/dma-fence.c
+++ b/drivers/dma-buf/dma-fence.c
@@ -244,6 +244,30 @@ 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
@@ -256,19 +280,12 @@ 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);

@@ -302,7 +319,6 @@ 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;
@@ -314,25 +330,14 @@ 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;
@@ -432,7 +437,6 @@ 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;
@@ -444,21 +448,9 @@ 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;
--
2.25.1


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