Re: [RFC PATCH for 5.8 1/4] sched: Fix unreliable rseq cpu_id for new tasks

[Florian Weimer]

* Mathieu Desnoyers:

> While integrating rseq into glibc and replacing glibc's sched_getcpu
> implementation with rseq, glibc's tests discovered an issue with
> incorrect __rseq_abi.cpu_id field value right after the first time
> a newly created process issues sched_setaffinity.
>
> For the records, it triggers after building glibc and running tests, and
> then issuing:
>
>   for x in {1..2000} ; do posix/tst-affinity-static  & done
>
> and shows up as:
>
> error: Unexpected CPU 2, expected 0
> error: Unexpected CPU 2, expected 0
> error: Unexpected CPU 2, expected 0
> error: Unexpected CPU 2, expected 0
> error: Unexpected CPU 138, expected 0
> error: Unexpected CPU 138, expected 0
> error: Unexpected CPU 138, expected 0
> error: Unexpected CPU 138, expected 0

As far as I can tell, the glibc reproducer no longer shows the issue
with this patch applied.

Tested-By: Florian Weimer <fweimer@xxxxxxxxxx>