Stale memory during post fork cow pmap update

[Mike Tancsa]

On 2/13/2018 8:30 AM, Konstantin Belousov wrote:
> Apparently Ryzen CPUs are able to demonstrate it quite reliably with the
> python driver for the samba build.  It was very surprising to me, esp.
> because I tried to understand the Ryzen bug for the whole last week and
> thought that it is more likely CPU store/load inconsistency than a software
> thing.  See https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=225584.
Just tested on an AMD EPYC 7281 (16/32 cores), and it runs into this bug
every time on the samba build.  Applying the referenced patch fixes the
problem, at least I was able to test 4 builds in a row without issue.

	---Mike


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Mike Tancsa, tel +1 519 651 3400 x203
Sentex Communications, mike at sentex.net
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