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From:   Florian Weimer <fw@deneb.enyo.de>
To:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        "Paul E . McKenney" <paulmck@linux.ibm.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        "H . Peter Anvin" <hpa@zytor.com>, Paul Turner <pjt@google.com>,
        linux-api@vger.kernel.org, Dmitry Vyukov <dvyukov@google.com>,
        Neel Natu <neelnatu@google.com>, stable@vger.kernel.org
Subject: Re: [RFC PATCH for 5.8 1/4] sched: Fix unreliable rseq cpu_id for new tasks
References: <20200706204913.20347-1-mathieu.desnoyers@efficios.com>
        <20200706204913.20347-2-mathieu.desnoyers@efficios.com>
Date:   Tue, 07 Jul 2020 09:30:13 +0200
In-Reply-To: <20200706204913.20347-2-mathieu.desnoyers@efficios.com> (Mathieu
        Desnoyers's message of "Mon, 6 Jul 2020 16:49:10 -0400")
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* 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@redhat.com>