Video freezes on Mac Pro: It was software after all

Posted by Pierre Igot in: Macintosh
January 21st, 2017 • 6:35 pm

I have an update on the situation with my Mac Pro that I blogged about in December

Back then, I indicated that the unpredictable video freezes that I had been experiencing for a while appeared to be gone after I had had one of my video cards replaced by Apple under warranty.

If you follow me on Twitter, you know that this is not where the story ends.

In fact, after the video card swap on December 11, the Mac behaved properly for exactly two weeks and then… out of the blue, I started experiencing video freezes again, on December 25. (Yes, on Christmas day!) The symptoms were exactly the same again: normal behaviour for a long time, and then, all of a sudden, a cascade of temporary video freezes, accompanied by the display of this error message in the system log:

Mac-Pro kernel[0]: stalling for detach from AMDTahitiGraphicsAccelerator

The video freezes would last several minutes, and then things would go back to normal… until the next time, which could be 15 minutes later, 12 hours later, or 72 hours later. There was no way to predict it.

How was this possible? This clearly indicated that the problem was not fixed by the video card swap, and that the “purple tinge” that the Genius Bar staff member had noticed with my video card when using his advanced testing tools was unrelated to the actual problem. Swapping the video card might have fixed the “purple tinge” (which I never experienced myself under normal conditions), but it didn’t fix the video freezes.

Needless to say, since the video freezes started happening on Christmas Day, I didn’t do anything about them right away. Apple’s services were closed on December 25 and 26 anyway, and I figured that they would be swamped with calls on December 27 from people with trivial problems with their new Apple-made Christmas gifts. So I knew I had to wait a few days.

I also was on holiday and didn’t exactly relish the thought of spending several hours of that time off on the phone with various Apple representatives trying to convince them to do something about the problem.

So I just continued using my computer normally, trying to put up with the freezes and not let them drive me mad. Then, the next time they happened, I noticed something that I hadn’t noticed before. One of the ways that the problem first manifested itself was not necessarily with a complete video freeze of the entire interface (except the mouse pointer), but with a web page failing to load in Safari. A page that I had just visited a moment ago and wanted to go back to wouldn’t load. Instead, I would be faced with a blank window, with no explanation. My Internet connection was still working fine, but Safari would refuse to load/display the web page. Somehow other web pages in other tabs or windows would still work fine for a while… And then eventually the video freezes would extend to the entire interface, and I would have to go through the entire thing again.

When this particular version of the problem occurred, it jigged my memory, and I remembered something that I hadn’t thought about in a while, which was that I had noticed a similar problem (web pages failing to load for no apparent reason) long before I started experiencing the video freezes affecting the entire user interface for extended periods. It had been fairly rare, and at the time, I had not tried to troubleshoot the problem, precisely because it was fairly rare and I had simply filed it under the “General Crappiness of Apple Software These Days” category (subcategory: “Impossible-to-Reproduce Crappy Software Problems for Which Bug Reporting Would Be a Waste of Time”).

But now, this new episode led me to think that, maybe, just maybe, the video freezes that I had been experiencing lately were just a more severe and intrusive manifestation of a long-standing problem… which in turn led me to think that, maybe, just maybe, it wasn’t a hardware problem after all.

I obviously couldn’t know for sure, but the theory that the video freezes were a software problem was worth revisiting…

But what could I do about it if it was a software problem? Well, I was still running El Capitan at the time, because my experience with early versions of Yosemite back in 2015 had made me extremely wary of being an early adopter of major system upgrades. My original plan had been to wait until version 10.12.3 of Sierra before trying it on my Mac Pro. Sierra was currently at 10.2.2. What if I took the chance and tried to install Sierra on my Mac Pro now, in order to see if, by any chance, the upgrade might, inadvertently or not, contain a fix for the video freezes?

I figured that I didn’t have too much to lose at that stage, and that if I didn’t do it now, there was a good chance that Apple’s representatives would ask me to try to do that anyway as part of the process of further troubleshooting the freezes.

So I took all the usual precautions (full backup, application upgrades that hadn’t been done yet, reading about potential problems with Sierra) and then I took the plunge, on December 26.

Well, today is January 21, and I am happy to report that I have not experienced a single recurrence of the video freezes accompanied by the “stalling for detach” error messages in the system log.

So it looks like Sierra (at least version 10.12.2) does contain a fix for the problem. As you can imagine, it’s a huge relief for me. I don’t have to go through the time-consuming process of trying to get Apple representatives to acknowledge the seriousness of the situation and provide me with a solution. I have a computer that works well again, and does not have a hardware flaw after all.

There is an epilogue to this story, however. Since December 26, I have heard from a fellow Twitter user who has been experiencing similar problems, albeit on a completely different machine (a MacBook Pro). She too has been experiencing video freezes, along with “stalling for detach” error messages in the system log. (In fact, it’s through a Google search for this phrase that she found my blog post about my problem.)

In her case, her MacBook Pro has video freezes and displays the following message in the log:

stalling for detach from AMDVerdeGraphicsAccelerator

Same message with a different flavour of graphics accelerator… We now had a clearly strong sign that the problem was indeed software and not hardware. (In retrospect, the very fact that the freezes were accompanied by error messages in the log was a sign that it was a software problem. Hardware problems typically occur at a level that the system is not even aware of, and cause freezes or kernel panics without a trace of the reason why in the logs.)

Still, like me, she was told by Apple that her video card might need to be replaced. She had just got it replaced, and based on my experience, I now warned her that there was a good chance that it wouldn’t fix the problem. Sure enough, two days later, she had more video freezes.

I told her that I had upgraded to Sierra and that it seemed to have fixed the problem, but that it was still too soon for me to tell for sure. (Now that nearly a month has elapsed, I am quite sure.)

She decided to stick with El Capitan for a while, because she was wary of the PDF-related issues reported with Sierra. (To be honest, the reports of bugs with Preview had also worried me quite a bit before then. However, while I do use PDFs in my work quite a bit, I haven’t really noticed any significant problems in my workflow with Sierra yet, and I have been back at work for two weeks now. Of course, your mileage may vary…)

And then…

On January 17, Apple released an updated version of Security Update 2016-003 for El Capitan, dubbed “Security Update 2016-003 Supplemental”. And guess what? The release notes indicated that the update to the update addressed “a kernel issue that could cause a Mac running El Capitan to occasionally freeze and become unresponsive”. Mmm…

Of course, when my own video freezes started getting serious, in November 2016, I did wonder whether any recent system update might have been the culprit. But the only update that I had installed during that time was an early build of that very security update, which I got as part of my involvement in the Apple Seed program. And since it was “only” a security update, and since my problem clearly seemed to be a video problem, I figured that there was no way that the two were linked. (I actually remember mentioning that update to the Apple senior representative who had taken care of me in December. He didn’t think there was a connection either.)

Now, of course, in light of these new developments, I do have to wonder whether my own video problems were not caused by that update. The timing seems to confirm it, except for the fact that I do remember experiencing the occasional blank page in Safari long before last fall… Still, it is also possible that there was an underlying problem before the security update, but that the security update just made it way, way worse, at least for some Macs.

Also, when you look at the details about the security update that Apple provides on this page, you can see that it contains fixes for security bugs that do involve things like “AppleGraphicsPowerManagement”, “CoreGraphics”, and “CoreMedia External Displays”. So it is not too far-fetched to think that the security update might have introduced (or amplified) low-level issues that did involve the video part of the system.

My Twitter friend has now installed the Supplemental version of the security update and, so far, she hasn’t experienced any further problems. It’s probably still a bit too soon to tell for sure. (I’d give it a whole month myself to be certain.) But it now appears quite likely that the video freezes that we both experienced, accompanied with these “stalling for detach” error messages in the system log, were not hardware problems, and were indeed either caused or made much worse by the original version of Security Update 2016-003, and that Security Update 2016-003 Supplemental does fix them.

Still, both she and I had to go through the process of dealing with (relatively) clueless Apple representatives and had to waste time getting our computers serviced for nothing. We might have got brand-new video cards out of the deal, but that does not, of course, compensate for all the grief caused by the bug.

And, as usual, I cannot help but wonder whether there is really nothing that Apple can do to improve its process for dealing with serious bugs. If this problem was indeed caused by Security Update 2016-003, why were the Apple representatives that we dealt with not aware of it? Why did they instead suggest useless hardware repairs? And why was the bug fixed silently without telling us? Where is the knowledge base article on Apple’s web site that describes the problem that we experienced in full detail, with clear reference to the exact symptoms and to the “stalling for detach” error messages in the system log?

What if other people are still experiencing the exact same problem and are looking for help today? How will they know to install Security Update 2016-003 Supplemental, especially if they are inclined to avoid installing new updates right away, precisely because they don’t trust that Apple can produce bug-free updates in the first place?

Something is rotten here, and other reports online about this lack of transparency tend to confirm it. Apple needs to realize that bugs cost us time, therefore money, and that, unlike their own representatives and senior representatives, we don’t get paid for the time we spend trying to work around these bugs or get them fixed.

Will we ever get a new attitude at Apple that not only transparently communicates about such crucial bugs, but also apologizes for the significant inconvenience that they cause?

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