From: Peter Zijlstra <peterz@infradead.org>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Joel Fernandes <joel@joelfernandes.org>,
linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
rostedt@goodmis.org, mingo@kernel.org,
gregkh@linuxfoundation.org, gustavo@embeddedor.com,
tglx@linutronix.de, josh@joshtriplett.org,
mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com
Subject: Re: [PATCH v2 3/9] rcu,tracing: Create trace_rcu_{enter,exit}()
Date: Tue, 18 Feb 2020 21:40:21 +0100 [thread overview]
Message-ID: <20200218204021.GJ11457@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20200218201728.GH2935@paulmck-ThinkPad-P72>
On Tue, Feb 18, 2020 at 12:17:28PM -0800, Paul E. McKenney wrote:
> On Tue, Feb 18, 2020 at 08:58:31PM +0100, Peter Zijlstra wrote:
> > On Thu, Feb 13, 2020 at 03:44:44PM -0500, Joel Fernandes wrote:
> >
> > > > > 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.
> >
> > > 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.
> >
> > > +__always_inline void rcu_nmi_exit(void)
> > > {
> > > struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
> > >
> > > @@ -651,25 +653,15 @@ static __always_inline void rcu_nmi_exit_common(bool irq)
> > > trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, atomic_read(&rdp->dynticks));
> > > WRITE_ONCE(rdp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */
> > >
> > > - if (irq)
> > > + if (!in_nmi())
> > > rcu_prepare_for_idle();
> > >
> > > rcu_dynticks_eqs_enter();
> > >
> > > - if (irq)
> > > + if (!in_nmi())
> > > rcu_dynticks_task_enter();
> > > }
> >
> > Boris and me have been going over the #MC code (and finding loads of
> > 'interesting' code) and ran into ist_enter(), whish has the following
> > code:
> >
> > /*
> > * We might have interrupted pretty much anything. In
> > * fact, if we're a machine check, we can even interrupt
> > * NMI processing. We don't want in_nmi() to return true,
> > * but we need to notify RCU.
> > */
> > rcu_nmi_enter();
> >
> >
> > Which, to me, sounds all sorts of broken. The IST (be it #DB or #MC) can
> > happen while we're holding all sorts of locks. This must be an NMI-like
> > context.
>
> Ouch! Looks like I need to hold off on getting rid of the "irq"
> parameters if in_nmi() isn't going to be accurate.
I'm currently trying to twist my brain around all this, because I
suspect it's all completely broken one way or another.
But yes, we definitely need to fix this before your patch goes in.
next prev parent reply other threads:[~2020-02-18 20:40 UTC|newest]
Thread overview: 82+ 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 21:01 ` Peter Zijlstra
2020-02-12 22:38 ` Joel Fernandes
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 21:01 ` 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 21:01 ` 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 20:44 ` 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 21:38 ` Steven Rostedt
2020-02-13 21:50 ` Paul E. McKenney
2020-02-13 21:50 ` Paul E. McKenney
2020-02-13 22:04 ` Steven Rostedt
2020-02-13 22:39 ` Paul E. McKenney
2020-02-14 6:19 ` Masami Hiramatsu
2020-02-15 14:59 ` Paul E. McKenney
2020-02-15 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 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 18:01 ` Masami Hiramatsu
2020-03-06 18:47 ` Joel Fernandes
2020-03-06 18:47 ` Joel Fernandes
2020-03-06 19:11 ` Joel Fernandes
2020-03-07 1:58 ` Masami Hiramatsu
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 22:58 ` Joel Fernandes
2020-02-13 23:55 ` Steven Rostedt
2020-02-18 19:58 ` Peter Zijlstra
2020-02-18 19:58 ` Peter Zijlstra
2020-02-18 20:17 ` Paul E. McKenney
2020-02-18 20:40 ` Peter Zijlstra [this message]
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
2020-02-12 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 ` 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 21:01 ` 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 ` 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 3:32 ` Steven Rostedt
2020-02-14 20:38 ` Kim Phillips
2020-02-14 22:48 ` Steven Rostedt
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