Bug 277795 – Gizmodo: 100% CPU and page doesn't fully load

• Component: Layout and Rendering
• Status: NEW

[Jeff Johnson]

Created attachment 472078 [details]
Spindump

https://gizmodo.com/your-microwave-could-be-a-haven-for-surprisingly-resilient-bacteria-2000484285

Safari 17.6 (19618.3.11.11.5) and Safari Technology Preview 200 (Safari 18.0, WebKit 19620.1.1 on macOS 14.6.1

Every time I load this URL, the Safari Web Content process takes >100% CPU, and when I scroll down the page, it becomes blank, not fully loaded. Attached is a spindump and a screenshot.

[Jeff Johnson]

Created attachment 472079 [details]
Screenshot

[Alexey Proskuryakov]

Doing a lot of work under MutationObserver::notifyMutationObservers.

I couldn't reproduce this in Safari 18. But suspecting a temporary website bug more than anything else. Does this still reproduce for you? And if it does, then does disabling extensions help?

[Jeff Johnson]

(In reply to Alexey Proskuryakov from comment #2)
> Doing a lot of work under MutationObserver::notifyMutationObservers.
> 
> I couldn't reproduce this in Safari 18. 

I can reproduce in Safari 18 on macOS 15, installed on another Mac.

> But suspecting a temporary website
> bug more than anything else. Does this still reproduce for you? 

Yes. It happens on basically every Gizmodo link.

> And if it
> does, then does disabling extensions help?

No.

[Alexey Proskuryakov]

Let's see if anyone else can reproduce, I still can not. I tried private browsing, too.

Mostly testing on a 14" M3, but a 16" Intel MacBook Pro on a different network also doesn't reproduce. Its scrolling is more janky, and there were some flashes of white, but only for a split second, not permanently stuck.

[Jeff Johnson]

I can't reproduce it anymore, so I guess the site changed.

[Jeff Johnson]

(In reply to Jeff Johnson from comment #5)
> I can't reproduce it anymore, so I guess the site changed.

It's started happening again. See also https://gizmodo.com/beyond-cpap-future-sleep-apnea-treatments-could-revolutionize-nighttime-health-2000484840 for example.

[Jeff Johnson]

Using Little Snitch, I've narrowed down the problem to ad.js loaded from https://clipcentric-a.akamaihd.net/ad/

If I block that script, there's no problem. If I allow that script, the problem occurs.

[Radar WebKit Bug Importer]

<rdar://problem/133931949>

[Karl Dubost]

Created attachment 472215 [details]
rendering in safari, firefox

I tried a couple of times with Safari and Firefox.
On Safari I get a peak at 100%+ but only for a couple of seconds then it goes back to normal. 

Firefox almost none, but they block more Ads per default.

[Jeff Johnson]

(In reply to Karl Dubost from comment #9)
> Created attachment 472215 [details]
> rendering in safari, firefox
> 
> I tried a couple of times with Safari and Firefox.
> On Safari I get a peak at 100%+ but only for a couple of seconds then it
> goes back to normal. 
> 
> Firefox almost none, but they block more Ads per default.

Make sure it has loaded ad.js from https://clipcentric-a.akamaihd.net/ad/ in the Network tab, because sometimes it does and sometimes it doesn't. It's loading right now, but it wasn't a few hours ago.

It's not clear how the screenshots of the top of the page are relevant, because you generally have to scroll down the page to reproduce.

[Karl Dubost]

For me unfortunately I haven't managed to get clipcentric in my tests. :( 


On the other hand, yes the page can get blank when scrolling fast, like if it was waiting to refresh the layout.

[Karl Dubost]

Hmm small correction, I can reproduce only when the Web Inspector is opened.

[Jeff Johnson]

(In reply to Karl Dubost from comment #11)
> For me unfortunately I haven't managed to get clipcentric in my tests. :( 

I can no longer reproduce with the pages I previously linked, but I can reproduce with the latest articles on Gizmodo. Perhaps the format is different for newer vs. older articles.

> On the other hand, yes the page can get blank when scrolling fast, like if
> it was waiting to refresh the layout.

It happens for me even when I scroll slowly.


> Hmm small correction, I can reproduce only when the Web Inspector is opened.

It happens for me with the web inspector closed too.

[Karl Dubost]

Ok I have finally been able to reproduce, Gizmodo is loading 10s of ads scripts and some seem to block rendering in some ways.

[Karl Dubost]

The most reliable way to reproduce for me was to 

1. with Safari TP 
2. Go to https://gizmodo.com/
3. Click on one of the latest articles on the right hand side column of the page.
4. Scroll. 

Result:
Sometimes the pages take a long time to load during scrolling.
If we let it rest after a couple of seconds it goes back to a normal behavior.

[Karl Dubost]

I get some rendering issues and delay for Chrome too, time to time, but not as bad as Safari in terms of rendering the content. The main content seems to have top priority over the ads. 

Same thing with Firefox, some ads a very long time to load, but doesn't block the main content.

[Jeff Johnson]

(In reply to Karl Dubost from comment #15)
> The most reliable way to reproduce for me was to 
> 
> 1. with Safari TP 
> 2. Go to https://gizmodo.com/
> 3. Click on one of the latest articles on the right hand side column of the
> page.
> 4. Scroll. 
> 
> Result:
> Sometimes the pages take a long time to load during scrolling.
> If we let it rest after a couple of seconds it goes back to a normal
> behavior.

In my case, the page never goes back to normal. It continues indefinitely with high CPU usage and blank white bottom.