From: Peter Zijlstra <peterz@infradead.org>
To: Qian Cai <cai@lca.pw>
Cc: mingo@redhat.com, juri.lelli@redhat.com,
vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
paulmck@kernel.org, tglx@linutronix.de, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] sched/core: fix illegal RCU from offline CPUs
Date: Mon, 20 Jan 2020 11:16:52 +0100 [thread overview]
Message-ID: <20200120101652.GM14879@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200113190331.12788-1-cai@lca.pw>
On Mon, Jan 13, 2020 at 02:03:31PM -0500, Qian Cai wrote:
> In the CPU-offline process, it calls mmdrop() after idle entry and the
> subsequent call to cpuhp_report_idle_dead(). Once execution passes the
> call to rcu_report_dead(), RCU is ignoring the CPU, which results in
> lockdep complaints when mmdrop() uses RCU from either memcg or
> debugobjects, so it by scheduling mmdrop() on another online CPU.
>
> According to the commit a79e53d85683 ("x86/mm: Fix pgd_lock deadlock"),
> mmdrop() is not interrupt-safe, and called from
> smp_call_function_single() could end up running mmdrop() from the IPI
> interrupt handler.
>
<deletes ~100 lines of gunk>
Surely the critical information contained in these nearly 100 lines of
splat can be more consicely represented?
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 90e4b00ace89..1863a6fc4d82 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -6194,7 +6194,8 @@ void idle_task_exit(void)
> current->active_mm = &init_mm;
> finish_arch_post_lock_switch();
> }
> - mmdrop(mm);
> + smp_call_function_single(cpumask_first(cpu_online_mask),
> + (void (*)(void *))mmdrop_async, mm, 0);
> }
Bah.. that's horrible. Surely we can find a better place to do this in
the whole hotplug machinery.
Perhaps you can have takedown_cpu() do the mmdrop()?
next prev parent reply other threads:[~2020-01-20 10:17 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-13 19:03 [PATCH v2] sched/core: fix illegal RCU from offline CPUs Qian Cai
2020-01-20 10:16 ` Peter Zijlstra [this message]
2020-01-20 20:35 ` Qian Cai
2020-01-21 10:35 ` Peter Zijlstra
2020-01-24 4:21 ` Qian Cai
2020-01-24 5:02 ` Matthew Wilcox
2020-03-30 2:42 ` Qian Cai
2020-04-01 21:05 ` Qian Cai
2020-04-01 21:40 Qian Cai
2020-04-02 11:24 ` Michael Ellerman
2020-04-02 14:00 ` Qian Cai
2020-04-02 15:54 ` Paul E. McKenney
2020-04-02 16:19 ` Qian Cai
2020-04-02 16:57 ` Paul E. McKenney
2020-04-17 13:26 ` Qian Cai
2020-04-21 13:56 ` Peter Zijlstra
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