From: joel@joelfernandes.org
To: Steven Rostedt <rostedt@goodmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"Gustavo A. R. Silva" <gustavo@embeddedor.com>,
Thomas Gleixner <tglx@linutronix.de>,
paulmck <paulmck@kernel.org>,
Josh Triplett <josh@joshtriplett.org>,
Lai Jiangshan <jiangshanlai@gmail.com>
Subject: Re: [PATCH] tracing/perf: Move rcu_irq_enter/exit_irqson() to perf trace point hook
Date: Mon, 10 Feb 2020 21:32:23 -0500 [thread overview]
Message-ID: <522406EB-8788-47F1-B616-0A6338A03304@joelfernandes.org> (raw)
In-Reply-To: <20200210212222.59a8c519@rorschach.local.home>
On February 10, 2020 9:22:22 PM EST, Steven Rostedt <rostedt@goodmis.org> wrote:
>
>> Which brings a question about handling of NMIs: in the proposed
>patch, if
>> a NMI nests over rcuidle context, AFAIU it will be in a state
>> !rcu_is_watching() && in_nmi(), which is handled by this patch with a
>simple
>> "return", meaning important NMIs doing hardware event sampling can be
>> completely lost.
>>
>> Considering that we cannot use rcu_irq_enter/exit_irqson() from NMI
>context,
>> is it at all valid to use rcu_read_lock/unlock() as perf does from
>NMI handlers,
>> considering that those can be nested on top of rcuidle context ?
>>
>
>Note, in the __DO_TRACE macro, we've had this for a long time:
>
> /* srcu can't be used from NMI */ \
> WARN_ON_ONCE(rcuidle && in_nmi()); \
>
>With nothing triggering.
I did not understand Mathieu's question, afaik perf event sampling code in NMI handler does not invoke trace_..._rcuidle functions anywhere. That afair is independently dealt within perf and does not involve tracepoint code. And if NMI has interrupted any code currently running in __DO_TRACE, that's ok because NMI is higher priority and will run to completion before resuming the interrupted code. Did I miss something? I am not surprised the warning doesn't ever trigger.
Thanks,
Joel.
>
>-- Steve
--
Sent from my Android device with K-9 Mail. Please excuse my brevity.
next prev parent reply other threads:[~2020-02-11 2:32 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-10 22:06 [PATCH] tracing/perf: Move rcu_irq_enter/exit_irqson() to perf trace point hook Steven Rostedt
2020-02-11 0:30 ` Mathieu Desnoyers
2020-02-11 2:22 ` Steven Rostedt
2020-02-11 2:32 ` joel [this message]
2020-02-11 15:19 ` Mathieu Desnoyers
2020-02-11 12:00 ` Peter Zijlstra
2020-02-11 13:03 ` Paul E. McKenney
2020-02-11 13:16 ` Peter Zijlstra
2020-02-11 13:23 ` Paul E. McKenney
2020-02-11 14:10 ` Steven Rostedt
2020-02-11 11:49 ` Peter Zijlstra
2020-02-11 12:59 ` Paul E. McKenney
2020-02-11 13:10 ` Peter Zijlstra
2020-02-11 13:20 ` Paul E. McKenney
2020-02-11 14:05 ` Steven Rostedt
2020-02-11 15:05 ` Peter Zijlstra
2020-02-11 15:29 ` Peter Zijlstra
2020-02-11 16:16 ` Steven Rostedt
2020-02-11 15:06 ` Paul E. McKenney
2020-02-11 15:31 ` Peter Zijlstra
2020-02-11 15:40 ` Paul E. McKenney
2020-02-11 12:21 ` Peter Zijlstra
2020-02-11 14:10 ` Steven Rostedt
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