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Fix race condition on metal backend with mCompletedSerial. 

There is currently a race condition in the metal backend with the
updating of `mCompletedSerial`. It is currently possible for the
`addCompletedHandler` to set to one value and then have the
`CheckAndUpdateCompletedSerial` call immediately set it back to
a lower value. This can then cause hangs as the serial never
correctly updates again.

This was happening on `dawn.node` when running a large number of
CTS test cases all at the same time.

Change-Id: I28fc58ab2b3737ca8039559718e539ce819e88bb
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/89780
Auto-Submit: Dan Sinclair <dsinclair@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
This commit is contained in:
dan sinclair 2022-05-11 15:15:55 +00:00 committed by Dawn LUCI CQ
parent 8e68f0aad7
commit 857f21e8b5
1 changed files with 11 additions and 6 deletions
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17
src/dawn/native/metal/DeviceMTL.mm
View File

@ -295,13 +295,18 @@ void Device::InitializeRenderPipelineAsyncImpl(Ref<RenderPipelineBase> renderPip
ResultOrError<ExecutionSerial> Device::CheckAndUpdateCompletedSerials() {
uint64_t frontendCompletedSerial{GetCompletedCommandSerial()};
if (frontendCompletedSerial > mCompletedSerial) {
// sometimes we increase the serials, in which case the completed serial in
// the device base will surpass the completed serial we have in the metal backend, so we
// must update ours when we see that the completed serial from device base has
// increased.
mCompletedSerial = frontendCompletedSerial;
// sometimes we increase the serials, in which case the completed serial in
// the device base will surpass the completed serial we have in the metal backend, so we
// must update ours when we see that the completed serial from device base has
// increased.
//
// This update has to be atomic otherwise there is a race with the `addCompletedHandler`
// call below and this call could set the mCompletedSerial backwards.
uint64_t current = mCompletedSerial.load();
while (frontendCompletedSerial > current &&
!mCompletedSerial.compare_exchange_weak(current, frontendCompletedSerial)) {
}
return ExecutionSerial(mCompletedSerial.load());
}