linux-kernel - Re: [RFC PATCH for 5.8 1/4] sched: Fix unreliable rseq cpu

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Date:   Tue, 7 Jul 2020 06:51:44 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Florian Weimer <fw@...eb.enyo.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        paulmck <paulmck@...ux.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        "H. Peter Anvin" <hpa@...or.com>, Paul Turner <pjt@...gle.com>,
        linux-api <linux-api@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Neel Natu <neelnatu@...gle.com>,
        stable <stable@...r.kernel.org>
Subject: 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@...eb.enyo.de wrote:

> * 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@...hat.com>

Thanks a lot Florian for your thorough review and testing !

Mathieu


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