From: Joel Fernandes <joel@joelfernandes.org>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.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: Thu, 13 Feb 2020 16:19:30 -0500 [thread overview]
Message-ID: <20200213211930.GG170680@google.com> (raw)
In-Reply-To: <20200213205442.GK2935@paulmck-ThinkPad-P72>
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.
thanks,
- Joel
> Thanx, Paul
>
> > ---8<-----------------------
> >
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index d91c9156fab2e..bbcc7767f18ee 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -614,16 +614,18 @@ void rcu_user_enter(void)
> > }
> > #endif /* CONFIG_NO_HZ_FULL */
> >
> > -/*
> > +/**
> > + * rcu_nmi_exit - inform RCU of exit from NMI context
> > + *
> > * If we are returning from the outermost NMI handler that interrupted an
> > * RCU-idle period, update rdp->dynticks and rdp->dynticks_nmi_nesting
> > * to let the RCU grace-period handling know that the CPU is back to
> > * being RCU-idle.
> > *
> > - * If you add or remove a call to rcu_nmi_exit_common(), be sure to test
> > + * If you add or remove a call to rcu_nmi_exit(), be sure to test
> > * with CONFIG_RCU_EQS_DEBUG=y.
> > */
> > -static __always_inline void rcu_nmi_exit_common(bool irq)
> > +__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();
> > }
> > -
> > -/**
> > - * rcu_nmi_exit - inform RCU of exit from NMI context
> > - *
> > - * If you add or remove a call to rcu_nmi_exit(), be sure to test
> > - * with CONFIG_RCU_EQS_DEBUG=y.
> > - */
> > -void rcu_nmi_exit(void)
> > -{
> > - rcu_nmi_exit_common(false);
> > -}
> > +NOKPROBE_SYMBOL(rcu_nmi_exit);
> >
> > /**
> > * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
> > @@ -693,7 +685,7 @@ void rcu_nmi_exit(void)
> > void rcu_irq_exit(void)
> > {
> > lockdep_assert_irqs_disabled();
> > - rcu_nmi_exit_common(true);
> > + rcu_nmi_exit();
> > }
> >
> > /*
> > @@ -777,7 +769,7 @@ void rcu_user_exit(void)
> > #endif /* CONFIG_NO_HZ_FULL */
> >
> > /**
> > - * rcu_nmi_enter_common - inform RCU of entry to NMI context
> > + * rcu_nmi_enter - inform RCU of entry to NMI context
> > * @irq: Is this call from rcu_irq_enter?
> > *
> > * If the CPU was idle from RCU's viewpoint, update rdp->dynticks and
> > @@ -786,10 +778,10 @@ void rcu_user_exit(void)
> > * long as the nesting level does not overflow an int. (You will probably
> > * run out of stack space first.)
> > *
> > - * If you add or remove a call to rcu_nmi_enter_common(), be sure to test
> > + * If you add or remove a call to rcu_nmi_enter(), be sure to test
> > * with CONFIG_RCU_EQS_DEBUG=y.
> > */
> > -static __always_inline void rcu_nmi_enter_common(bool irq)
> > +__always_inline void rcu_nmi_enter(void)
> > {
> > long incby = 2;
> > struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
> > @@ -807,12 +799,12 @@ static __always_inline void rcu_nmi_enter_common(bool irq)
> > */
> > if (rcu_dynticks_curr_cpu_in_eqs()) {
> >
> > - if (irq)
> > + if (!in_nmi())
> > rcu_dynticks_task_exit();
> >
> > rcu_dynticks_eqs_exit();
> >
> > - if (irq)
> > + if (!in_nmi())
> > rcu_cleanup_after_idle();
> >
> > incby = 1;
> > @@ -834,14 +826,6 @@ static __always_inline void rcu_nmi_enter_common(bool irq)
> > rdp->dynticks_nmi_nesting + incby);
> > barrier();
> > }
> > -
> > -/**
> > - * rcu_nmi_enter - inform RCU of entry to NMI context
> > - */
> > -void rcu_nmi_enter(void)
> > -{
> > - rcu_nmi_enter_common(false);
> > -}
> > NOKPROBE_SYMBOL(rcu_nmi_enter);
> >
> > /**
> > @@ -869,7 +853,7 @@ NOKPROBE_SYMBOL(rcu_nmi_enter);
> > void rcu_irq_enter(void)
> > {
> > lockdep_assert_irqs_disabled();
> > - rcu_nmi_enter_common(true);
> > + rcu_nmi_enter();
> > }
> >
> > /*
next prev parent reply other threads:[~2020-02-13 21:19 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 [this message]
2020-02-13 21:38 ` Steven Rostedt
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
2020-02-17 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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