From: Valentin Schneider <valentin.schneider@arm.com>
To: Qian Cai <cai@lca.pw>
Cc: Mel Gorman <mgorman@techsingularity.net>,
Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Juri Lelli <juri.lelli@redhat.com>,
Steven Rostedt <rostedt@goodmis.org>,
paulmck@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: suspicious RCU due to "Prefer using an idle CPU as a migration target instead of comparing tasks"
Date: Thu, 27 Feb 2020 15:26:41 +0000 [thread overview]
Message-ID: <jhjimjsvyoe.mognet@arm.com> (raw)
In-Reply-To: <1582814862.7365.135.camel@lca.pw>
On Thu, Feb 27 2020, Qian Cai wrote:
> On Thu, 2020-02-27 at 09:09 -0500, Qian Cai wrote:
>> The linux-next commit ff7db0bf24db ("sched/numa: Prefer using an idle CPU as a
>> migration target instead of comparing tasks") introduced a boot warning,
>
> This?
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index a61d83ea2930..ca780cd1eae2 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1607,7 +1607,9 @@ static void update_numa_stats(struct task_numa_env *env,
> if (ns->idle_cpu == -1)
> ns->idle_cpu = cpu;
>
> +rcu_read_lock();
> idle_core = numa_idle_core(idle_core, cpu);
> +rcu_read_unlock();
> }
> }
>
Hmph right, we have
numa_idle_core()->test_idle_cores()->rcu_dereference().
Dunno if it's preferable to wrap the entirety of update_numa_stats() or
if that fine-grained read-side section is ok.
next prev parent reply other threads:[~2020-02-27 15:26 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-27 14:09 suspicious RCU due to "Prefer using an idle CPU as a migration target instead of comparing tasks" Qian Cai
2020-02-27 14:47 ` Qian Cai
2020-02-27 15:26 ` Valentin Schneider [this message]
2020-02-27 16:35 ` Qian Cai
2020-02-27 16:47 ` Qian Cai
2020-02-27 17:19 ` Mel Gorman
2020-02-27 17:30 ` Valentin Schneider
2020-02-27 18:56 ` Paul E. McKenney
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