Failure in stdlib/tst-arc4random-thread testing glibc 2.41 for release.

[Carlos O'Donell]

Adhemerval,

In testing glibc 2.41 for release I had this fail in a *very* surprising way:
https://sourceware.org/glibc/wiki/Testing/Tests/stdlib/tst-arc4random-thread

System is a local Lenovo P16v laptop under testing load:

info: outer_threads=2 inner_threads=4
info: arc4random: minimum of 163840 blob results expected
info: arc4random: 163894 blob results observed
error: arc4random: duplicate blob: "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000" (16 bytes)
  first source: thread -1, index 0
  second source: thread -1, index 1
info: arc4random_buf: minimum of 163840 blob results expected
info: arc4random_buf: 163840 blob results observed
info: arc4random_uniform: minimum of 163840 blob results expected
info: arc4random_uniform: 163840 blob results observed
error: 1 test failures

Processor is a AMD Ryzen 7 PRO 7840HS (16 cpus).

Distribution used is Fedora 41.

I would not have expected to see a duplicate blob at all, and it left me
wondering if we had a test issue under load.

I've filed it as a failure for 2.41, and something we need to keep an eye
on because either it's a serious issue (arc4random not returning randomness)
or a test issue.

Kernel is Linux fedora 6.11.11-300.fc41.x86_64.

glibc tree is just rebased.

Thoughts?

-- 
Cheers,
Carlos.