From: Steven Rostedt <rostedt@goodmis.org>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Joel Fernandes <joel@joelfernandes.org>,
Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
mingo@kernel.org, gregkh@linuxfoundation.org,
gustavo@embeddedor.com, tglx@linutronix.de,
josh@joshtriplett.org, mathieu.desnoyers@efficios.com,
jiangshanlai@gmail.com, Masami Hiramatsu <mhiramat@kernel.org>
Subject: Re: [PATCH v2 3/9] rcu,tracing: Create trace_rcu_{enter,exit}()
Date: Thu, 13 Feb 2020 17:04:51 -0500 [thread overview]
Message-ID: <20200213170451.690c4e5c@gandalf.local.home> (raw)
In-Reply-To: <20200213215004.GM2935@paulmck-ThinkPad-P72>
On Thu, 13 Feb 2020 13:50:04 -0800
"Paul E. McKenney" <paulmck@kernel.org> wrote:
> On Thu, Feb 13, 2020 at 04:38:25PM -0500, Steven Rostedt wrote:
> > [ Added Masami ]
> >
> > On Thu, 13 Feb 2020 16:19:30 -0500
> > Joel Fernandes <joel@joelfernandes.org> wrote:
> >
> > > On Thu, Feb 13, 2020 at 12:54:42PM -0800, Paul E. McKenney wrote:
> > > > On Thu, Feb 13, 2020 at 03:44:44PM -0500, Joel Fernandes wrote:
> > > > > On Thu, Feb 13, 2020 at 10:56:12AM -0800, Paul E. McKenney wrote:
> > > > > [...]
> > > > > > > > It might well be that I could make these functions be NMI-safe, but
> > > > > > > > rcu_prepare_for_idle() in particular would be a bit ugly at best.
> > > > > > > > So, before looking into that, I have a question. Given these proposed
> > > > > > > > changes, will rcu_nmi_exit_common() and rcu_nmi_enter_common() be able
> > > > > > > > to just use in_nmi()?
> > > > > > >
> > > > > > > That _should_ already be the case today. That is, if we end up in a
> > > > > > > tracer and in_nmi() is unreliable we're already screwed anyway.
> > > > > >
> > > > > > So something like this, then? This is untested, probably doesn't even
> > > > > > build, and could use some careful review from both Peter and Steve,
> > > > > > at least. As in the below is the second version of the patch, the first
> > > > > > having been missing a couple of important "!" characters.
> > > > >
> > > > > I removed the static from rcu_nmi_enter()/exit() as it is called from
> > > > > outside, that makes it build now. Updated below is Paul's diff. I also added
> > > > > NOKPROBE_SYMBOL() to rcu_nmi_exit() to match rcu_nmi_enter() since it seemed
> > > > > asymmetric.
> > > >
> > > > My compiler complained about the static and the __always_inline, so I
> > > > fixed those. But please help me out on adding the NOKPROBE_SYMBOL()
> > > > to rcu_nmi_exit(). What bad thing happens if we leave this on only
> > > > rcu_nmi_enter()?
> > >
> > > It seemed odd to me we were not allowing kprobe on the rcu_nmi_enter() but
> > > allowing it on exit (from a code reading standpoint) so my reaction was to
> > > add it to both, but we could probably keep that as a separate
> > > patch/discussion since it is slightly unrelated to the patch.. Sorry to
> > > confuse the topic.
> > >
> >
> > rcu_nmi_enter() was marked NOKPROBE or other reasons. See commit
> > c13324a505c77 ("x86/kprobes: Prohibit probing on functions before
> > kprobe_int3_handler()")
> >
> > The issue was that we must not allow anything in do_int3() call kprobe
> > code before kprobe_int3_handler() is called. Because ist_enter() (in
> > do_int3()) calls rcu_nmi_enter() it had to be marked NOKPROBE. It had
> > nothing to do with it being RCU nor NMI, but because it was simply
> > called in do_int3().
> >
> > Thus, there's no reason to make rcu_nmi_exit() NOKPROBE. But a commont
> > to why rcu_nmi_enter() would probably be useful, like below:
>
> Thank you, Steve! Could I please have your Signed-off-by for this?
Sure, but it was untested ;-)
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
I'd like a Reviewed-by from Masami though.
-- Steve
next prev parent reply other threads:[~2020-02-13 22:04 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-12 21:01 [PATCH v2 0/9] tracing vs rcu vs nmi Peter Zijlstra
2020-02-12 21:01 ` [PATCH v2 1/9] rcu: Rename rcu_irq_{enter,exit}_irqson() Peter Zijlstra
2020-02-12 22:38 ` Joel Fernandes
2020-02-12 21:01 ` [PATCH v2 2/9] rcu: Mark rcu_dynticks_curr_cpu_in_eqs() inline Peter Zijlstra
2020-02-12 22:38 ` Joel Fernandes
2020-02-13 1:41 ` Steven Rostedt
2020-02-13 14:25 ` Joel Fernandes
2020-02-12 21:01 ` [PATCH v2 3/9] rcu,tracing: Create trace_rcu_{enter,exit}() Peter Zijlstra
2020-02-12 23:20 ` Joel Fernandes
2020-02-13 8:27 ` Peter Zijlstra
2020-02-13 13:31 ` Joel Fernandes
2020-02-13 13:51 ` Paul E. McKenney
2020-02-13 16:40 ` Peter Zijlstra
2020-02-13 18:56 ` Paul E. McKenney
2020-02-13 20:44 ` Joel Fernandes
2020-02-13 20:54 ` Paul E. McKenney
2020-02-13 21:19 ` Joel Fernandes
2020-02-13 21:38 ` Steven Rostedt
2020-02-13 21:50 ` Paul E. McKenney
2020-02-13 22:04 ` Steven Rostedt [this message]
2020-02-13 22:39 ` Paul E. McKenney
2020-02-14 6:19 ` Masami Hiramatsu
2020-02-15 14:59 ` Paul E. McKenney
2020-02-17 8:55 ` Masami Hiramatsu
2020-02-17 16:31 ` Paul E. McKenney
2020-02-18 4:33 ` Masami Hiramatsu
2020-02-18 16:12 ` Paul E. McKenney
2020-02-18 16:15 ` Mathieu Desnoyers
2020-02-18 16:35 ` Steven Rostedt
2020-02-18 17:46 ` Steven Rostedt
2020-02-18 20:18 ` Paul E. McKenney
2020-02-19 2:45 ` Masami Hiramatsu
2020-03-06 18:01 ` Masami Hiramatsu
2020-03-06 18:47 ` Joel Fernandes
2020-03-06 19:11 ` Joel Fernandes
2020-03-07 1:58 ` Masami Hiramatsu
2020-03-06 0:42 ` Thomas Gleixner
2020-02-13 21:48 ` Paul E. McKenney
2020-02-13 22:58 ` Joel Fernandes
2020-02-13 23:55 ` Steven Rostedt
2020-02-18 19:58 ` Peter Zijlstra
2020-02-18 20:17 ` Paul E. McKenney
2020-02-18 20:40 ` Peter Zijlstra
2020-02-18 21:39 ` Paul E. McKenney
2020-02-19 9:57 ` Peter Zijlstra
2020-02-19 12:46 ` Paul E. McKenney
2020-02-12 23:27 ` Joel Fernandes
2020-02-13 8:28 ` Peter Zijlstra
2020-02-13 18:39 ` Joel Fernandes
2020-02-12 21:01 ` [PATCH v2 4/9] sched,rcu,tracing: Avoid tracing before in_nmi() is correct Peter Zijlstra
2020-02-12 21:01 ` [PATCH v2 5/9] x86,tracing: Add comments to do_nmi() Peter Zijlstra
2020-02-12 21:01 ` [PATCH v2 6/9] perf,tracing: Prepare the perf-trace interface for RCU changes Peter Zijlstra
2020-02-12 23:28 ` Joel Fernandes
2020-02-13 8:29 ` Peter Zijlstra
2020-02-13 18:38 ` Joel Fernandes
2020-02-12 21:01 ` [PATCH v2 7/9] tracing: Employ trace_rcu_{enter,exit}() Peter Zijlstra
2020-02-12 21:01 ` [PATCH v2 8/9] tracing: Remove regular RCU context for _rcuidle tracepoints (again) Peter Zijlstra
2020-02-12 21:01 ` [PATCH v2 9/9] perf,tracing: Allow function tracing when !RCU Peter Zijlstra
2020-02-14 2:28 ` Sergey Senozhatsky
2020-02-14 2:42 ` Sergey Senozhatsky
2020-02-14 3:32 ` Steven Rostedt
2020-02-14 20:38 ` Kim Phillips
2020-02-14 22:48 ` Steven Rostedt
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