1554022 - Intermittent /css/cssom-view/elementScroll.html | Element scrollBy test (one argument) - assert_equals: increment of scrollTop should be 15 expected 90 but got 89

Status: RESOLVED FIXED

(Core :: DOM: CSS Object Model, defect, P5)

Description

[Treeherder Bug Filer]

Filed by: aciure [at] mozilla.com
Parsed log: https://treeherder.mozilla.org/logviewer.html#?job_id=248072946&repo=mozilla-central
Full log: https://queue.taskcluster.net/v1/task/KO0CmD5NT9e-axyIuYpBOQ/runs/0/artifacts/public/logs/live_backing.log

---

[task 2019-05-23T23:21:14.924Z] 23:21:14 INFO - TEST-PASS | /css/cssom-view/elementScroll.html | Element scrollBy test (two arguments)
[task 2019-05-23T23:21:14.924Z] 23:21:14 INFO - TEST-UNEXPECTED-FAIL | /css/cssom-view/elementScroll.html | Element scrollBy test (one argument) - assert_equals: increment of scrollTop should be 15 expected 90 but got 89
[task 2019-05-23T23:21:14.925Z] 23:21:14 INFO - window.onload/<@http://web-platform.test:8000/css/cssom-view/elementScroll.html:137:13
[task 2019-05-23T23:21:14.925Z] 23:21:14 INFO - Test.prototype.step@http://web-platform.test:8000/resources/testharness.js:1587:25
[task 2019-05-23T23:21:14.925Z] 23:21:14 INFO - test@http://web-platform.test:8000/resources/testharness.js:544:30
[task 2019-05-23T23:21:14.925Z] 23:21:14 INFO - window.onload@http://web-platform.test:8000/css/cssom-view/elementScroll.html:128:9
[task 2019-05-23T23:21:15.146Z] 23:21:15 INFO - .
[task 2019-05-23T23:21:15.146Z] 23:21:15 INFO - TEST-OK | /css/cssom-view/elementScroll.html | took 600ms
[task 2019-05-23T23:21:15.887Z] 23:21:15 INFO - Closing logging queue
[task 2019-05-23T23:21:15.887Z] 23:21:15 INFO - queue closed
[task 2019-05-23T23:21:15.903Z] 23:21:15 INFO - Setting up ssl
[task 2019-05-23T23:21:15.919Z] 23:21:15 INFO - certutil |
[task 2019-05-23T23:21:15.934Z] 23:21:15 INFO - certutil |
[task 2019-05-23T23:21:15.950Z] 23:21:15 INFO - certutil |
[task 2019-05-23T23:21:15.950Z] 23:21:15 INFO - Certificate Nickname Trust Attributes
[task 2019-05-23T23:21:15.950Z] 23:21:15 INFO - SSL,S/MIME,JAR/XPI
[task 2019-05-23T23:21:15.950Z] 23:21:15 INFO -
[task 2019-05-23T23:21:15.950Z] 23:21:15 INFO - web-platform-tests CT,,
[task 2019-05-23T23:21:15.950Z] 23:21:15 INFO -
[task 2019-05-23T23:21:17.679Z] 23:21:17 INFO - adb Granting important runtime permissions to org.mozilla.geckoview.test
[task 2019-05-23T23:21:18.928Z] 23:21:18 INFO - adb launch_application: am start -W -n org.mozilla.geckoview.test/org.mozilla.geckoview.test.TestRunnerActivity -a android.intent.action.MAIN --es env9 MOZ_PROCESS_LOG=/tmp/tmp5gTuGtpidlog --es env8 MOZ_CRASHREPORTER_NO_REPORT=1 --es args "-no-remote -profile /sdcard/tests/profile --marionette about:blank" --es env3 STYLO_THREADS=4 --es env2 MOZ_HIDE_RESULTS_TABLE=1 --es env1 R_LOG_VERBOSE=1 --es env0 MOZ_CRASHREPORTER=1 --es env7 MOZ_DISABLE_NONLOCAL_CONNECTIONS=1 --es env6 R_LOG_DESTINATION=stderr --es env5 MOZ_CRASHREPORTER_SHUTDOWN=1 --es env4 MOZ_LOG=signaling:3,mtransport:4,DataChannel:4,jsep:4 --ez use_multiprocess True --es env10 R_LOG_LEVEL=6
[task 2019-05-23T23:21:20.768Z] 23:21:20 INFO - Starting runner

Comment 1

[Andreea Pavel [:apavel]]

Seems to be from bug 1553022, appeared on this merge: https://hg.mozilla.org/mozilla-central/pushloghtml?changeset=d551d37b9ad0dd1c8ad2e87c74344f623fc4b694

Hiroyuki can you take a look?

Comment 2

[Hiroyuki Ikezoe (:hiro)]

Sure.

Comment 3

[Hiroyuki Ikezoe (:hiro)]

Hmm, weird. I can't reproduce the failure locally at all. Initially I tried on android-emulator-x86, but after that, I noticed our CI uses android-emulator-x86-64, so I also tried on the 64bits emulator, but can't reproduce either. Then I suspected that the device screen size is not the same as CI's, but as per a log in our CI, it's exactly the same.

hw.lcd.width = 800
hw.lcd.height = 1280
hw.lcd.depth = 16
hw.lcd.density = 320

Comment 4

[Intermittent Failures Robot]

24 failures in 4730 pushes (0.005 failures/push) were associated with this bug in the last 7 days.

Repository breakdown:

• mozilla-central: 24

Platform breakdown:

• android-em-7-0-x86_64: 24

For more details, see:
https://treeherder.mozilla.org/intermittent-failures.html#/bugdetails?bug=1554022&startday=2019-05-20&endday=2019-05-26&tree=all

Comment 5

[Hiroyuki Ikezoe (:hiro)]

I can replicate the failure on local linux box with layout.css.devPixelsPerPx=1.61. And it turns out it's an underlying issue. And there is another issue that I just filed (bug 1554604).

Anyway, the problem here is;

1. We store the scroll position as nsPoint
2. We clamp the scroll position to the layer pixels in ClampAndAlignWithLayerPixels
3. We get the current scroll position in app units in ScrollByCSSPixels and add the given delta value to the current value in app units

So, it's possible that the added value is slightly far from the ideal position in CSS pixels, and also it's possible that the added value is clamped to positions where it's farther from the ideal position in ClampAndAlignWithLayerPixels.

To prevent this calculation error, we should get the current position in CSS pixels in ScrollByCSSPixels.

https://treeherder.mozilla.org/#/jobs?repo=try&revision=8b9ff110c940cc7d40db862fa6e8e29ca40fecac

Comment 6

[Hiroyuki Ikezoe (:hiro)]

The try looks good. The test in question in wpt5, all wpt5s are orange but it's due to bug 1551382.

Comment 7

[Hiroyuki Ikezoe (:hiro)]

Attachment: Bug 1554022 - Use the current position in CSS pixels for the start point of ScrollBy. r?botond

Otherwise clamped positions in layer pixels might cause 1-pixel difference
in CSS pixels on Android.

Comment 8

[Intermittent Failures Robot]

60 failures in 4337 pushes (0.014 failures/push) were associated with this bug in the last 7 days.

This is the #32 most frequent failure this week.

** This failure happened more than 30 times this week! Resolving this bug is a high priority. **

** Try to resolve this bug as soon as possible. If unresolved for 2 weeks, the affected test(s) may be disabled. **

Repository breakdown:

• mozilla-central: 58
• autoland: 2

Platform breakdown:

• android-em-7-0-x86_64: 60

For more details, see:
https://treeherder.mozilla.org/intermittent-failures.html#/bugdetails?bug=1554022&startday=2019-05-27&endday=2019-06-02&tree=all

Comment 9

[Intermittent Failures Robot]

15 failures in 930 pushes (0.016 failures/push) were associated with this bug yesterday.

Repository breakdown:

• mozilla-central: 13
• try: 2

Platform breakdown:

• android-em-7-0-x86_64: 15

For more details, see:
https://treeherder.mozilla.org/intermittent-failures.html#/bugdetails?bug=1554022&startday=2019-06-04&endday=2019-06-04&tree=all

Comment 10

[Hiroyuki Ikezoe (:hiro)]

For future references;

Though this failure caused by bug 1553022, but the real cause is bug 1556685 which is a pre-existing issue on the layer-pixel alignment, and the reason why we hadn't realized it is that we've been incorrectly applying the layer-pixel alignment (bug 1556683) on Fennec, to be more precise on non-E10S.

Also note that I've noticed that window.scrollBy clamps the given double value in CSS pixels, but it doesn't use NStoIntRound() so that it might be possible there are some edge cases where the clamped value is different from what element.scrollBy does.

Comment 11

[Intermittent Failures Robot]

44 failures in 5197 pushes (0.008 failures/push) were associated with this bug in the last 7 days.

This is the #47 most frequent failure this week.

** This failure happened more than 30 times this week! Resolving this bug is a high priority. **

** Try to resolve this bug as soon as possible. If unresolved for 2 weeks, the affected test(s) may be disabled. **

Repository breakdown:

• mozilla-central: 31
• try: 13

Platform breakdown:

• android-em-7-0-x86_64: 44

For more details, see:
https://treeherder.mozilla.org/intermittent-failures.html#/bugdetails?bug=1554022&startday=2019-06-03&endday=2019-06-09&tree=all

Comment 12

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/bdb43da73c35
Use the current position in CSS pixels for the start point of ScrollBy. r=botond,mstange

Comment 13

[Dorel Luca [:dluca]]

https://hg.mozilla.org/mozilla-central/rev/bdb43da73c35