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

----- On Jul 7, 2020, at 3:30 AM, Florian Weimer fw@deneb.enyo.de wrote:

* Mathieu Desnoyers:

quoted

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 <redacted>

Thanks a lot Florian for your thorough review and testing !

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com