Hi team, I noticed this while trying to import 'compositing' test cases from WPT upstream: Link - https://ews-build.s3-us-west-2.amazonaws.com/GTK-WK2-Tests-EWS/d6deb037-98528-stress-mode/imported/w3c/web-platform-tests/css/compositing/mix-blend-mode/mix-blend-mode-parent-element-overflow-hidden-and-border-radius-2-crash-log.txt ***** STDERR: ASSERTION FAILED: !backgroundClip.affectedByRadius() STDERR: /app/webkit/Source/WebCore/rendering/RenderLayerCompositor.cpp(3636) : WebCore::RenderLayerCompositor::computeAncestorClippingStack(const WebCore::RenderLayer&, const WebCore::RenderLayer*) const::<lambda(const WebCore::RenderLayer&, const WebCore::RenderLayer&, WebCore::ShouldRespectOverflowClip)> STDERR: 1 0x7fc092a185a4 WebCore::RenderLayerCompositor::computeAncestorClippingStack(WebCore::RenderLayer const&, WebCore::RenderLayer const*) const::{lambda(WebCore::RenderLayer const&, WebCore::RenderLayer const&, WebCore::ShouldRespectOverflowClip)#1}::operator()(WebCore::RenderLayer const&, WebCore::RenderLayer const&, WebCore::ShouldRespectOverflowClip) const STDERR: 2 0x7fc092a18a91 WebCore::RenderLayerCompositor::computeAncestorClippingStack(WebCore::RenderLayer const&, WebCore::RenderLayer const*) const STDERR: 3 0x7fc092a18e16 WebCore::RenderLayerCompositor::updateAncestorClippingStack(WebCore::RenderLayer const&, WebCore::RenderLayer const*) const STDERR: 4 0x7fc092a1913b WebCore::RenderLayerBacking::updateAncestorClipping(bool, WebCore::RenderLayer const*) STDERR: 5 0x7fc092a41cc0 WebCore::RenderLayerBacking::updateConfiguration(WebCore::RenderLayer const*) STDERR: 6 0x7fc092a4ee2f WebCore::RenderLayerCompositor::updateBackingAndHierarchy(WebCore::RenderLayer&, WTF::Vector<WTF::Ref<WebCore::GraphicsLayer, WTF::RawPtrTraits<WebCore::GraphicsLayer>, WTF::DefaultRefDerefTraits<WebCore::GraphicsLayer> >, 0ul, WTF::CrashOnOverflow, 16ul, WTF::FastMalloc>&, WebCore::RenderLayerCompositor::UpdateBackingTraversalState&, WebCore::ScrollingTreeState&, WTF::OptionSet<WebCore::RenderLayerCompositor::UpdateLevel>) STDERR: 7 0x7fc092a4f19d WebCore::RenderLayerCompositor::updateBackingAndHierarchy(WebCore::RenderLayer&, WTF::Vector<WTF::Ref<WebCore::GraphicsLayer, WTF::RawPtrTraits<WebCore::GraphicsLayer>, WTF::DefaultRefDerefTraits<WebCore::GraphicsLayer> >, 0ul, WTF::CrashOnOverflow, 16ul, WTF::FastMalloc>&, WebCore::RenderLayerCompositor::UpdateBackingTraversalState&, WebCore::ScrollingTreeState&, WTF::OptionSet<WebCore::RenderLayerCompositor::UpdateLevel>) STDERR: 8 0x7fc092a4f19d WebCore::RenderLayerCompositor::updateBackingAndHierarchy(WebCore::RenderLayer&, WTF::Vector<WTF::Ref<WebCore::GraphicsLayer, WTF::RawPtrTraits<WebCore::GraphicsLayer>, WTF::DefaultRefDerefTraits<WebCore::GraphicsLayer> >, 0ul, WTF::CrashOnOverflow, 16ul, WTF::FastMalloc>&, WebCore::RenderLayerCompositor::UpdateBackingTraversalState&, WebCore::ScrollingTreeState&, WTF::OptionSet<WebCore::RenderLayerCompositor::UpdateLevel>) STDERR: 9 0x7fc092a4f19d WebCore::RenderLayerCompositor::updateBackingAndHierarchy(WebCore::RenderLayer&, WTF::Vector<WTF::Ref<WebCore::GraphicsLayer, WTF::RawPtrTraits<WebCore::GraphicsLayer>, WTF::DefaultRefDerefTraits<WebCore::GraphicsLayer> >, 0ul, WTF::CrashOnOverflow, 16ul, WTF::FastMalloc>&, WebCore::RenderLayerCompositor::UpdateBackingTraversalState&, WebCore::ScrollingTreeState&, WTF::OptionSet<WebCore::RenderLayerCompositor::UpdateLevel>) STDERR: 10 0x7fc092a5011d WebCore::RenderLayerCompositor::updateCompositingLayers(WebCore::CompositingUpdateType, WebCore::RenderLayer*) STDERR: 11 0x7fc092194b64 WebCore::LocalFrameViewLayoutContext::updateCompositingLayersAfterLayoutIfNeeded() STDERR: 12 0x7fc091675ae1 WebCore::Document::implicitClose() STDERR: 13 0x7fc091f7fcf8 WebCore::FrameLoader::checkCallImplicitClose() STDERR: 14 0x7fc091f9b5cf WebCore::FrameLoader::checkCompleted() STDERR: 15 0x7fc091f9b7fc WebCore::FrameLoader::finishedParsing() STDERR: 16 0x7fc09167f411 WebCore::Document::finishedParsing() STDERR: 17 0x7fc091c98d78 WebCore::HTMLConstructionSite::finishedParsing() STDERR: 18 0x7fc091cbe112 WebCore::HTMLDocumentParser::prepareToStopParsing() STDERR: 19 0x7fc091f494a4 WebCore::DocumentWriter::end() STDERR: 20 0x7fc091f6550b WebCore::DocumentLoader::finishedLoading() STDERR: 21 0x7fc0920729fd WebCore::CachedResource::checkNotify(WebCore::NetworkLoadMetrics const&, WebCore::LoadWillContinueInAnotherProcess) [clone .part.0] STDERR: 22 0x7fc09205c692 WebCore::CachedRawResource::finishLoading(WebCore::FragmentedSharedBuffer const*, WebCore::NetworkLoadMetrics const&) STDERR: 23 0x7fc0920298fd WebCore::SubresourceLoader::didFinishLoading(WebCore::NetworkLoadMetrics const&) STDERR: 24 0x7fc08f019abe WebKit::WebResourceLoader::didFinishResourceLoad(WebCore::NetworkLoadMetrics&&) STDERR: 25 0x7fc08e3f07dd void IPC::handleMessage<Messages::WebResourceLoader::DidFinishResourceLoad, IPC::Connection, WebKit::WebResourceLoader, WebKit::WebResourceLoader, void (WebCore::NetworkLoadMetrics&&)>(IPC::Connection&, IPC::Decoder&, WebKit::WebResourceLoader*, void (WebKit::WebResourceLoader::*)(WebCore::NetworkLoadMetrics&&)) [clone .isra.0] STDERR: 26 0x7fc08e3f381c WebKit::WebResourceLoader::didReceiveMessage(IPC::Connection&, IPC::Decoder&) STDERR: 27 0x7fc08f02c070 WebKit::NetworkProcessConnection::dispatchMessage(IPC::Connection&, IPC::Decoder&) STDERR: 28 0x7fc08e3ee256 WebKit::NetworkProcessConnection::didReceiveMessage(IPC::Connection&, IPC::Decoder&) STDERR: 29 0x7fc08e9b57de IPC::Connection::dispatchMessage(IPC::Decoder&) STDERR: 30 0x7fc08e9b88ad IPC::Connection::dispatchMessage(WTF::UniqueRef<IPC::Decoder>) [clone .part.0] STDERR: 31 0x7fc08e9b901f IPC::Connection::dispatchOneIncomingMessage() STDERR: WebKitWebProcess terminated (pid 3938) for reason: crash **** Importing PR - https://github.com/WebKit/WebKit/pull/48865 I will skip it before landing (so don't worry about TestExpectation management but good to raise bug). Thanks!