layout/fonts: Mitigate races related to quirks mode and fallback fonts by mrobinson · Pull Request #42960 · servo/servo

mrobinson · 2026-03-02T16:52:15Z

This change includes two related fixes for flakiness revealed by #42847.

When caching fonts, try harder to not re-cache a font. This could
happen due to a race condition with the read-write lock on the font
cache. This change improves memory usage in some cases as it prevents
a font from being loaded twice.
Incorporate both the strut size and the block size contribution of a
previously unused font in an inline container. Before the code was
incorporating one or the other. In addition, only incorporate the
block contribution of a previously unused font if its metrics
meaningfully differ from the container's default font. This was the
case triggered by failing to have the fix in part one of the change.

Testing: This fixes flakiness in an internal WPT-style test.
Fixes: #42908.

This change includes two related fixes for flakiness revealed by servo#42847. 1. When caching fonts, try harder to not re-cache a font. This could happen due to a race condition with the read-write lock on the font cache. This change improves memory usage in some cases as it prevents a font from being loaded twice. 2. Incorporate both the strut size and the block size contribution of a previously unused font in an inline container. Before the code was incorporating one or the other. In addition, *only* incorporate the block contribution of a previously unused font if its metrics meaningfully differ from the container's default font. This was the case triggered by failing to have the fix in part one of the change. Co-authored-by: Oriol Brufau <[email protected]> Co-authored-by: Luke Warlow <[email protected]> Signed-off-by: Martin Robinson <[email protected]>

github-actions · 2026-03-02T16:56:23Z

🔨 Triggering try run (#22586420167) for Linux (WPT)

github-actions · 2026-03-02T18:04:28Z

Test results for linux-wpt from try job (#22586420167):

Flaky unexpected result (31)

TIMEOUT /FileAPI/url/url-in-tags-revoke.window.html (#19978)
- TIMEOUT [expected PASS] subtest: Fetching a blob URL immediately before revoking it works in <script> tags.
```
Test timed out
```
OK [expected TIMEOUT] /IndexedDB/idbfactory_open.any.worker.html
- PASS [expected FAIL] subtest: Calling open() with version argument 1.5 should not throw.
- PASS [expected TIMEOUT] subtest: Calling open() with version argument 9007199254740991 should not throw.
- PASS [expected TIMEOUT] subtest: Calling open() with version argument undefined should not throw.
OK /_mozilla/mozilla/getBoundingClientRect.html (#39668)
- FAIL [expected PASS] subtest: getBoundingClientRect 1
```
assert_equals: expected 62 but got 60.35
```
CRASH [expected OK] /_webgl/conformance/uniforms/no-over-optimization-on-uniform-array-05.html
TIMEOUT [expected OK] /credential-management/credentialscontainer-frame-basics.https.html (#39430)
- TIMEOUT [expected FAIL] subtest: navigator.credentials should be undefined in documents generated from data: URLs.
```
Test timed out
```
OK /css/css-cascade/layer-cssom-order-reverse.html (#36094)
- PASS [expected FAIL] subtest: Delete layer invalidates @font-face
OK [expected ERROR] /fetch/fetch-later/quota/same-origin-iframe/multiple-iframes.https.window.html (#35176)
OK /fetch/metadata/generated/css-font-face.sub.tentative.html (#34624)
- PASS [expected FAIL] subtest: sec-fetch-storage-access - Not sent to non-trustworthy same-origin destination
OK [expected ERROR] /fetch/metadata/window-open.https.sub.html (#40339)
- FAIL [expected PASS] subtest: Cross-site window, forced, reloaded
```
The operation is insecure.
```
OK [expected ERROR] /focus/focus-event-after-switching-iframes.sub.html (#40368)
CRASH [expected OK] /html/browsers/browsing-the-web/navigating-across-documents/005.html (#27062)
OK /html/browsers/browsing-the-web/navigating-across-documents/navigation-unload-cross-origin.sub.window.html (#29056)
- PASS [expected FAIL] subtest: Cross-origin navigation started from unload handler must be ignored
OK /html/browsers/browsing-the-web/navigating-across-documents/replace-before-load/a-click.html (#28697)
- PASS [expected FAIL] subtest: aElement.click() before the load event must NOT replace
OK /html/browsers/history/the-history-interface/traverse_the_history_3.html (#21383)
- PASS [expected FAIL] subtest: Multiple history traversals, last would be aborted
TIMEOUT [expected OK] /html/interaction/focus/the-autofocus-attribute/document-with-fragment-empty.html (#28259)
- TIMEOUT [expected FAIL] subtest: Autofocus elements in top-level browsing context's documents with empty fragments should work.
```
Test timed out
```
OK /html/semantics/document-metadata/the-meta-element/pragma-directives/attr-meta-http-equiv-refresh/allow-scripts-flag-changing-1.html (#39694)
- PASS [expected FAIL] subtest: Meta refresh is blocked by the allow-scripts sandbox flag at its creation time, not when refresh comes due
OK /html/semantics/embedded-content/the-iframe-element/iframe-loading-lazy-nav-location-replace-set-src.html (#32697)
- PASS [expected FAIL] subtest: Navigating iframe loading='lazy' and then setting src: location.replace
TIMEOUT [expected OK] /html/semantics/embedded-content/the-iframe-element/iframe_sandbox_navigate_other_frame_popup.sub.html (#39702)
- TIMEOUT [expected FAIL] subtest: Sandboxed iframe can not navigate other frame's popup
```
Test timed out
```
OK /html/semantics/scripting-1/the-script-element/module/dynamic-import/blob-url.any.worker.html (#33909)
- FAIL [expected PASS] subtest: Revoking a blob URL immediately after calling import will not fail
```
promise_test: Unhandled rejection with value: object "TypeError: Module fetching failed"
```
TIMEOUT [expected OK] /html/user-activation/navigation-state-reset-sameorigin.html
- TIMEOUT [expected PASS] subtest: Post-navigation state reset.
```
Test timed out
```
CRASH [expected OK] /html/webappapis/scripting/reporterror.any.worker.html
OK /navigation-timing/test-navigation-type-reload.html (#33334)
- PASS [expected FAIL] subtest: Reload domComplete > Original domComplete
- PASS [expected FAIL] subtest: Reload domContentLoadedEventEnd > Original domContentLoadedEventEnd
- PASS [expected FAIL] subtest: Reload domContentLoadedEventStart > Original domContentLoadedEventStart
- PASS [expected FAIL] subtest: Reload fetchStart > Original fetchStart
- PASS [expected FAIL] subtest: Reload loadEventEnd > Original loadEventEnd
- PASS [expected FAIL] subtest: Reload loadEventStart > Original loadEventStart
PASS [expected FAIL] /png/apng/acTL-plays-two.html (#41191)
OK /resource-timing/buffer-full-add-then-clear.html (#40819)
- FAIL [expected PASS] subtest: Test that if the buffer is cleared after entries were added to the secondary buffer, those entries make it into the primary one
```
assert_equals: Number of entries does not match the expected value. expected 3 but got 0
```
OK /resource-timing/test_resource_timing.html (#25720)
- PASS [expected FAIL] subtest: PerformanceEntry has correct name, initiatorType, startTime, and duration (xmlhttprequest)
TIMEOUT /trusted-types/trusted-types-navigation.html?06-10 (#37920)
- TIMEOUT [expected FAIL] subtest: Navigate a frame via anchor with javascript:-urls in report-only mode.
```
Test timed out
```
- NOTRUN [expected TIMEOUT] subtest: Navigate a frame via anchor with javascript:-urls w/ default policy in report-only mode.
TIMEOUT [expected OK] /visual-viewport/resize-event-order.html (#41981)
- TIMEOUT [expected FAIL] subtest: Popup: DOMWindow resize fired before VisualViewport.
```
Test timed out
```
- NOTRUN [expected PASS] subtest: iframe: DOMWindow resize fired before VisualViewport.
CRASH [expected OK] /webaudio/the-audio-api/the-mediastreamaudiodestinationnode-interface/closed-audiocontext-construction.html
OK /webdriver/tests/classic/element_click/user_prompts.py
- FAIL [expected PASS] subtest: test_accept[alert-None]
```
webdriver.error.NoSuchWindowException: no such window (404): No such window
```
OK /webdriver/tests/classic/element_send_keys/send_keys.py
- FAIL [expected PASS] subtest: test_null_parameter_value
```
webdriver.error.NoSuchWindowException: no such window (404): No such window
```
OK /webdriver/tests/classic/new_window/new.py
- ERROR [expected PASS] subtest: test_no_top_browsing_context
```
setup error: webdriver.error.NoSuchElementException: no such element (404)
```

Stable unexpected results that are known to be intermittent (16)

FAIL [expected PASS] /_mozilla/mozilla/sslfail.html (#10760)
TIMEOUT [expected OK] /_mozilla/mozilla/window_resize_event.html (#36741)
- TIMEOUT [expected PASS] subtest: Popup onresize event fires after resizeTo
```
Test timed out
```
OK /_webgl/conformance/textures/misc/texture-upload-size.html (#21770)
- PASS [expected FAIL] subtest: WebGL test #45
- PASS [expected FAIL] subtest: WebGL test #47
- PASS [expected FAIL] subtest: WebGL test #49
- PASS [expected FAIL] subtest: WebGL test #51
- FAIL [expected PASS] subtest: WebGL test #53
```
assert_true: Texture was smaller than the expected size 2x2 expected true got false
```
- FAIL [expected PASS] subtest: WebGL test #55
```
assert_true: getError expected: INVALID_VALUE. Was NO_ERROR : when calling texSubImage2D with the same texture upload with offset 1, 1 expected true got false
```
- FAIL [expected PASS] subtest: WebGL test #57
```
assert_true: Texture was smaller than the expected size 2x2 expected true got false
```
- FAIL [expected PASS] subtest: WebGL test #59
```
assert_true: getError expected: INVALID_VALUE. Was NO_ERROR : when calling texSubImage2D with the same texture upload with offset 1, 1 expected true got false
```
- PASS [expected FAIL] subtest: WebGL test #61
- PASS [expected FAIL] subtest: WebGL test #63
- And 18 more unexpected results...

ERROR [expected CRASH] /_webgl/conformance2/textures/misc/tex-3d-size-limit.html (#42881)

PASS [expected FAIL] subtest: WebGL test #1

FAIL [expected PASS] subtest: WebGL test #3

assert_true: getError expected: INVALID_VALUE. Was NO_ERROR : texImage3D should fail for dimension out of range. expected true got false

FAIL [expected PASS] subtest: WebGL test #4

assert_true: getError expected: INVALID_VALUE. Was NO_ERROR : texImage3D should fail for dimension out of range. expected true got false

FAIL [expected PASS] subtest: WebGL test #5

assert_true: getError expected: INVALID_VALUE. Was NO_ERROR : texImage3D should fail for dimension out of range. expected true got false

FAIL [expected PASS] subtest: WebGL test #6

assert_true: getError expected: INVALID_VALUE. Was NO_ERROR : texImage3D should fail for dimension out of range. expected true got false

FAIL [expected PASS] subtest: WebGL test #7

assert_true: getError expected: INVALID_VALUE. Was NO_ERROR : texImage3D should fail for dimension out of range. expected true got false

FAIL [expected PASS] subtest: WebGL test #8

assert_true: getError expected: INVALID_VALUE. Was NO_ERROR : texImage3D should fail for dimension out of range. expected true got false

FAIL [expected PASS] subtest: WebGL test #9

assert_true: getError expected: INVALID_VALUE. Was NO_ERROR : texImage3D should fail for dimension out of range. expected true got false

FAIL [expected PASS] subtest: WebGL test #10

assert_true: getError expected: INVALID_VALUE. Was NO_ERROR : texImage3D should fail for dimension out of range. expected true got false

FAIL [expected PASS] subtest: WebGL test #11

assert_true: getError expected: INVALID_VALUE. Was NO_ERROR : texImage3D should fail for dimension out of range. expected true got false

And 27 more unexpected results...

OK /beacon/beacon-basic.https.window.html (#41723)
- PASS [expected FAIL] subtest: Payload size restriction should be accumulated: type = string
OK /css/css-fonts/generic-family-keywords-001.html (#37467)
- PASS [expected FAIL] subtest: @font-face matching for quoted and unquoted generic(fangsong)
- FAIL [expected PASS] subtest: @font-face matching for quoted and unquoted generic(kai)
```
assert_equals: quoted generic(kai) matches  @font-face rule expected 30 but got 50
```
- FAIL [expected PASS] subtest: @font-face matching for quoted and unquoted generic(khmer-mul)
```
assert_equals: quoted generic(khmer-mul) matches  @font-face rule expected 30 but got 50
```
- FAIL [expected PASS] subtest: @font-face matching for quoted and unquoted generic(nastaliq)
```
assert_equals: quoted generic(nastaliq) matches  @font-face rule expected 30 but got 50
```
OK /css/css-fonts/generic-family-keywords-003.html (#38994)
- PASS [expected FAIL] subtest: @font-face matching for quoted and unquoted sans-serif (drawing text in a canvas)
- PASS [expected FAIL] subtest: @font-face matching for quoted and unquoted cursive (drawing text in a canvas)
- PASS [expected FAIL] subtest: @font-face matching for quoted and unquoted fantasy (drawing text in a canvas)
- PASS [expected FAIL] subtest: @font-face matching for quoted and unquoted monospace (drawing text in a canvas)
- PASS [expected FAIL] subtest: @font-face matching for quoted and unquoted system-ui (drawing text in a canvas)
- PASS [expected FAIL] subtest: @font-face matching for quoted and unquoted math (drawing text in a canvas)
- PASS [expected FAIL] subtest: @font-face matching for quoted and unquoted generic(fangsong) (drawing text in a canvas)
- PASS [expected FAIL] subtest: @font-face matching for quoted and unquoted generic(khmer-mul) (drawing text in a canvas)
- PASS [expected FAIL] subtest: @font-face matching for quoted and unquoted ui-serif (drawing text in a canvas)
TIMEOUT [expected OK] /fetch/api/redirect/redirect-keepalive.https.any.html (#32153)
- TIMEOUT [expected PASS] subtest: [keepalive][iframe][load] mixed content redirect; setting up
```
Test timed out
```
ERROR [expected OK] /fetch/fetch-later/quota/same-origin-iframe/accumulated-oversized-payload.https.window.html (#41705)
OK /html/browsers/browsing-the-web/navigating-across-documents/navigation-unload-same-origin-fragment.html (#20768)
- FAIL [expected PASS] subtest: Tests that a fragment navigation in the unload handler will not block the initial navigation
```
assert_equals: expected "" but got "#fragment"
```
OK /html/browsers/browsing-the-web/navigating-across-documents/navigation-unload-same-origin.window.html (#29049)
- FAIL [expected PASS] subtest: Same-origin navigation started from unload handler must be ignored
```
assert_equals: expected "?pass" but got "?fail"
```

OK [expected TIMEOUT] /html/interaction/focus/the-autofocus-attribute/supported-elements.html (#24145)

FAIL [expected NOTRUN] subtest: Host element with delegatesFocus should support autofocus

assert_equals: expected Element node &lt;div autofocus=""&gt;&lt;/div&gt; but got Element node &lt;body&gt;&lt;div autofocus=""&gt;&lt;/div&gt;&lt;/body&gt;

FAIL [expected NOTRUN] subtest: Host element with delegatesFocus including no focusable descendants should be skipped

assert_equals: expected Element node &lt;input autofocus=""&gt;&lt;/input&gt; but got Element node &lt;body&gt;&lt;/body&gt;

FAIL [expected NOTRUN] subtest: Area element should support autofocus

assert_equals: expected Element node &lt;area autofocus="" href="/common/blank.html"&gt;&lt;/area&gt; but got Element node &lt;body&gt;
&lt;img src="/media/poster.png" usemap="#map"&gt;
&lt;map n...

OK /html/semantics/scripting-1/the-script-element/execution-timing/077.html (#22139)

FAIL [expected PASS] subtest: adding several types of scripts through the DOM and removing some of them confuses scheduler

assert_array_equals: expected property 1 to be "Script #1 ran" but got "Script #3 ran" (expected array ["Script #2 ran", "Script #1 ran", "Script #3 ran", "Script #4 ran"] got ["Script #2 ran", "Script #3 ran", "Script #4 ran", "Script #1 ran"])

OK /html/webappapis/user-prompts/print-during-unload.html (#35944)
- PASS [expected FAIL] subtest: print() during unload
TIMEOUT /trusted-types/trusted-types-navigation.html?31-35 (#38034)
- TIMEOUT [expected PASS] subtest: Navigate a frame via form-submission with javascript:-urls in report-only mode.
```
Test timed out
```
OK [expected TIMEOUT] /webstorage/localstorage-about-blank-3P-iframe-opens-3P-window.partitioned.html (#29053)
- PASS [expected TIMEOUT] subtest: StorageKey: test 3P about:blank window opened from a 3P iframe

github-actions · 2026-03-02T18:05:35Z

✨ Try run (#22586420167) succeeded.

mrobinson requested review from Loirooriol and nicoburns as code owners March 2, 2026 16:52

servo-highfive added the S-awaiting-review There is new code that needs to be reviewed. label Mar 2, 2026

Loirooriol added the T-linux-wpt Do a try run of the WPT label Mar 2, 2026

github-actions bot removed the T-linux-wpt Do a try run of the WPT label Mar 2, 2026

Loirooriol approved these changes Mar 3, 2026

View reviewed changes

servo-highfive removed the S-awaiting-review There is new code that needs to be reviewed. label Mar 3, 2026

mrobinson added this pull request to the merge queue Mar 3, 2026

servo-highfive added the S-awaiting-merge The PR is in the process of compiling and running tests on the automated CI. label Mar 3, 2026

Merged via the queue into servo:main with commit 027910e Mar 3, 2026
71 checks passed

mrobinson deleted the font-cache-race-condition branch March 3, 2026 21:59

servo-highfive removed the S-awaiting-merge The PR is in the process of compiling and running tests on the automated CI. label Mar 3, 2026

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layout/fonts: Mitigate races related to quirks mode and fallback fonts#42960

layout/fonts: Mitigate races related to quirks mode and fallback fonts#42960
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