#48121·servo

Test case from #47834 with selection click-and-drag produces LCP related crash intermittently

Author: webbedspaceCreated Sep 16, 2026Updated Sep 16, 2026

LabelsI-panicA-perf-measurement

Describe the bug: This only has to do with clicking and dragging a selection across some text, I think.

To Reproduce: The test case is:

xml

<!doctype html>
<script>
document.write(`<div style="display:grid;grid-template-columns:1fr 1fr">${[
	"charset", "import", "layer", "namespace", "counter-style", "container", "font-face",
	"font-feature-values", "keyframes", "-webkit-keyframes", "page", "position-try", "property",
	"scope", "starting-style", "supports", "view-transition"
].map(type =>
	`<code>${type}</code><b>${CSS.supports(`at-rule(@${type})`)}</b>`
).join('')}`)</script>

Load this with --pref largest_contentful_paint_enabled and then click and drag a selection. I tended to drag vertically across multiple lines. This crash is sometimes immediately produced on Windows:

Element for LCP entry should be non-null (thread Script#1, at components\script\dom\performance\largestcontentfulpaint.rs:55)
   0: mozilla::detail::ConditionVariableImpl::~ConditionVariableImpl
   1: mozilla::detail::ConditionVariableImpl::~ConditionVariableImpl
   2: mozilla::detail::ConditionVariableImpl::~ConditionVariableImpl
   3: mozilla::detail::ConditionVariableImpl::~ConditionVariableImpl
   4: mozilla::detail::ConditionVariableImpl::~ConditionVariableImpl
   5: mozilla::detail::ConditionVariableImpl::~ConditionVariableImpl
   6: mozilla::detail::ConditionVariableImpl::~ConditionVariableImpl
   7: mozilla::detail::ConditionVariableImpl::~ConditionVariableImpl
   8: mozilla::detail::ConditionVariableImpl::~ConditionVariableImpl
   9: mozilla::NowIncludingSuspendMs
  10: mozilla::NowIncludingSuspendMs
  11: mozilla::detail::ConditionVariableImpl::~ConditionVariableImpl
  12: mozilla::detail::ConditionVariableImpl::~ConditionVariableImpl
  13: mozilla::detail::ConditionVariableImpl::~ConditionVariableImpl
  14: mozilla::detail::ConditionVariableImpl::~ConditionVariableImpl
  15: mozilla::detail::ConditionVariableImpl::~ConditionVariableImpl
  16: mozilla::detail::ConditionVariableImpl::~ConditionVariableImpl
  17: BaseThreadInitThunk
  18: RtlUserThreadStart
[2026-09-16T07:17:09Z ERROR servoshell::panic_hook] Element for LCP entry should be non-null
[2026-09-16T07:17:09Z ERROR servo_constellation::event_loop] Did not successfully request EventLoop exit: Disconnected

I did 12 runs and produced this crash about 5 times.

Here is footage of one attempt https://github.com/user-attachments/assets/5c0f4c65-3612-449d-8ea8-1705491e34d8

Platform: Windows 10, Servo today

Source: servo/servo

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