From: Steven Rostedt <rostedt@goodmis.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
"Joel Fernandes (Google)" <joel@joelfernandes.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"Gustavo A. R. Silva" <gustavo@embeddedor.com>,
Thomas Gleixner <tglx@linutronix.de>,
"Paul E. McKenney" <paulmck@kernel.org>,
Josh Triplett <josh@joshtriplett.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Lai Jiangshan <jiangshanlai@gmail.com>
Subject: Re: [PATCH] tracing/perf: Move rcu_irq_enter/exit_irqson() to perf trace point hook
Date: Tue, 11 Feb 2020 09:05:03 -0500 [thread overview]
Message-ID: <20200211090503.68c0d70f@gandalf.local.home> (raw)
In-Reply-To: <20200211114954.GK14914@hirez.programming.kicks-ass.net>
On Tue, 11 Feb 2020 12:49:54 +0100
Peter Zijlstra <peterz@infradead.org> wrote:
> On Mon, Feb 10, 2020 at 05:06:43PM -0500, Steven Rostedt wrote:
> > + if (!rcu_watching) { \
> > + /* Can not use RCU if rcu is not watching and in NMI */ \
> > + if (in_nmi()) \
> > + return; \
> > + rcu_irq_enter_irqson(); \
> > + } \
>
> I saw the same weirdness in __trace_stack(), and I'm confused by it.
>
> How can we ever get to: in_nmi() && !rcu_watching() ? That should be a
> BUG. In particular, nmi_enter() has rcu_nmi_enter().
>
> Paul, can that really happen?
The stack tracer connects to the function tracer and is called at all
the places that function tracing can be called from. As I like being
able to trace RCU internal functions (especially as they are complex),
I don't want to set them all to notrace. But, for callbacks that
require RCU to be watching, we need this check, because there's some
internal state that we can be in an NMI and RCU is not watching (as
there's some places in nmi_enter that can be traced!).
And if we are tracing preempt_enable and preempt_disable (as Joel added
trace events there), it may be the case for trace events too.
-- Steve
next prev parent reply other threads:[~2020-02-11 14:05 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
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 [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200211090503.68c0d70f@gandalf.local.home \
--to=rostedt@goodmis.org \
--cc=gregkh@linuxfoundation.org \
--cc=gustavo@embeddedor.com \
--cc=jiangshanlai@gmail.com \
--cc=joel@joelfernandes.org \
--cc=josh@joshtriplett.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mathieu.desnoyers@efficios.com \
--cc=mingo@kernel.org \
--cc=paulmck@kernel.org \
--cc=peterz@infradead.org \
--cc=tglx@linutronix.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).