Bug 1432562 - Memtest86+ reports false positive memory errors
Summary: Memtest86+ reports false positive memory errors
Alias: None
Product: Fedora
Classification: Fedora
Component: memtest86+
Version: 25
Hardware: x86_64
OS: Linux
Target Milestone: ---
Assignee: Jaroslav Škarvada
QA Contact: Fedora Extras Quality Assurance
Depends On:
TreeView+ depends on / blocked
Reported: 2017-03-15 16:58 UTC by Marc Muehlfeld
Modified: 2017-12-12 10:45 UTC (History)
2 users (show)

Fixed In Version:
Doc Type: If docs needed, set a value
Doc Text:
Clone Of:
Last Closed: 2017-12-12 10:45:06 UTC

Attachments (Terms of Use)
Screenshot (one run of test 7) (171.42 KB, image/jpeg)
2017-03-15 16:58 UTC, Marc Muehlfeld
no flags Details
Screenshot (188.34 KB, image/jpeg)
2017-03-15 17:02 UTC, Marc Muehlfeld
no flags Details
Screenshot with SMP disabled (143.15 KB, image/jpeg)
2017-03-15 17:11 UTC, Marc Muehlfeld
no flags Details

Description Marc Muehlfeld 2017-03-15 16:58:09 UTC
Created attachment 1263397 [details]
Screenshot (one run of test 7)

Description of problem:
When I run Memtest86+ 5.01 on my new computer, the utility reports in almost each run 32 errors in test 7 (block move). I think it must be a false positive, because:

* I have two equal memory modules, I tested separately. For both test 7 fails and all errors are within the first 1 MB. First I thought the modules are broken and asked Kingston to replace them. However, even for the new ones the same problems are reported. I think it's very unlikely that 4 modules have exactly the same problem.

* The mainboard vendor officially list the memory module as compatible.

* The same problem was reported for Passmark Memtest86 in 2013:
  They fixed the problem with a workaround (see comment 15). See also the background details in the release notes linked in this comment.

* I run Memtest 86 7.3 Free Edition 4 hours (4 runs) and no errors were found. Also memtester, did not find any problems.

Version-Release number of selected component (if applicable):
memtest86+ 5.01

How reproducible:

Steps to Reproduce:
1. Boot PC with one or both RAM modules into Memtest86+
2. Wait until test 7 is executed.
   Alternatively you can only select test 7 and limit the test range from 0 to 1 MB.

Actual results:
32 errors are reported in almost every run.

Expected results:
No errors should be shown if the hardware is OK.

Additional info:
  Mainboard: Gigabyte GA-Z270-HD3P, BIOS F4 (previously F2)
  CPU: Intel i7-7700
  RAM: Kingston HyperX HX424C15FB/16
Gigabyte officially lists the CPU and the RAM modules as compatible.

I also tested it after resetting the BIOS to defaults.

Comment 1 Marc Muehlfeld 2017-03-15 17:02:45 UTC
Created attachment 1263399 [details]

This is how it looks if I only run "test 7" and only on the reported area (0 - 1MB) for more than 10000 loops.

Comment 2 Marc Muehlfeld 2017-03-15 17:11:42 UTC
Created attachment 1263400 [details]
Screenshot with SMP disabled

If I disable SMP, no errors are reported (not even after 6400 passes).

This sounds like the same problem that was fixed in Passmark Memtest86. See #c0.

Comment 3 Jaroslav Škarvada 2017-03-15 17:37:19 UTC
Thanks for info, but it seems like HW problem, from the Passmark release notes:

It turned out the problem was more elusive that we expected. Basically when multiple threads are running the CPU registers get corrupted. They appear to spontaneously become corrupted during the test. Causing a flood of errors. People generally encountered the problem at Test #3 as this was the first test to use multi-threading. But the other tests had similar problems. We don't know if this is a CPU errata, a bug in the way multi-threading is setup, non maskable hardware interrupts messing up the CPU's state or something more subtle. Part of the problem is also that the available debugging techniques (as MemTest86 runs without having an operating system being loaded) are extremely basic. Debugging the code probably even worse than it was in the DOS3.3 days.

So the work-around implemented was to change the default CPU selection mode to round robin. In this mode only one CPU is used at a time, but after each test the CPU in use is rotated. So all CPUs will still get used, but only after a longer period of time.

If I understand it correctly the workaround consists in effectively turning multi-threaded test to single-threaded? Too bad. Unfortunately I do not have the affected HW so I cannot look onto it myself. Also if I am not mistaken the default running mode in Fedora is single core, so you shouldn't encounter the problem if you use the default mode. The SMP mode is still experimental and needs to be explicitly selected.

Comment 4 Fedora End Of Life 2017-11-16 19:48:36 UTC
This message is a reminder that Fedora 25 is nearing its end of life.
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Comment 5 Fedora End Of Life 2017-12-12 10:45:06 UTC
Fedora 25 changed to end-of-life (EOL) status on 2017-12-12. Fedora 25 is
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