From: "Paul E. McKenney" <paulmck@kernel.org>
To: Frederic Weisbecker <frederic@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>, Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
netdev@vger.kernel.org, bpf@vger.kernel.org,
lkml <linux-kernel@vger.kernel.org>,
Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
Yonghong Song <yhs@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@chromium.org>,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH bpf-next 1/2] cpuidle/rcu: Making arch_cpu_idle and rcu_idle_exit noinstr
Date: Mon, 16 May 2022 06:39:36 -0700 [thread overview]
Message-ID: <20220516133936.GW1790663@paulmck-ThinkPad-P17-Gen-1> (raw)
In-Reply-To: <20220516114922.GA349949@lothringen>
On Mon, May 16, 2022 at 01:49:22PM +0200, Frederic Weisbecker wrote:
> On Sun, May 15, 2022 at 09:25:35PM -0700, Paul E. McKenney wrote:
> > On Sun, May 15, 2022 at 10:36:52PM +0200, Jiri Olsa wrote:
> > > Making arch_cpu_idle and rcu_idle_exit noinstr. Both functions run
> > > in rcu 'not watching' context and if there's tracer attached to
> > > them, which uses rcu (e.g. kprobe multi interface) it will hit RCU
> > > warning like:
> > >
> > > [ 3.017540] WARNING: suspicious RCU usage
> > > ...
> > > [ 3.018363] kprobe_multi_link_handler+0x68/0x1c0
> > > [ 3.018364] ? kprobe_multi_link_handler+0x3e/0x1c0
> > > [ 3.018366] ? arch_cpu_idle_dead+0x10/0x10
> > > [ 3.018367] ? arch_cpu_idle_dead+0x10/0x10
> > > [ 3.018371] fprobe_handler.part.0+0xab/0x150
> > > [ 3.018374] 0xffffffffa00080c8
> > > [ 3.018393] ? arch_cpu_idle+0x5/0x10
> > > [ 3.018398] arch_cpu_idle+0x5/0x10
> > > [ 3.018399] default_idle_call+0x59/0x90
> > > [ 3.018401] do_idle+0x1c3/0x1d0
> > >
> > > The call path is following:
> > >
> > > default_idle_call
> > > rcu_idle_enter
> > > arch_cpu_idle
> > > rcu_idle_exit
> > >
> > > The arch_cpu_idle and rcu_idle_exit are the only ones from above
> > > path that are traceble and cause this problem on my setup.
> > >
> > > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> >
> > From an RCU viewpoint:
> >
> > Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
> >
> > [ I considered asking for an instrumentation_on() in rcu_idle_exit(),
> > but there is no point given that local_irq_restore() isn't something
> > you instrument anyway. ]
>
> So local_irq_save() in the beginning of rcu_idle_exit() is unsafe because
> it is instrumentable by the function (graph) tracers and the irqsoff tracer.
>
> Also it calls into lockdep that might make use of RCU.
>
> That's why rcu_idle_exit() is not noinstr yet. See this patch:
>
> https://lore.kernel.org/lkml/20220503100051.2799723-4-frederic@kernel.org/
Ah, I should have looked at the context-tracking series again!
And I have to ask... How much debugging capability are we really losing
by continuing to use the raw versions of local_irq_{save,restore}()?
Thanx, Paul
> Thanks.
>
> >
> > > ---
> > > arch/x86/kernel/process.c | 2 +-
> > > kernel/rcu/tree.c | 2 +-
> > > 2 files changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> > > index b370767f5b19..1345cb0124a6 100644
> > > --- a/arch/x86/kernel/process.c
> > > +++ b/arch/x86/kernel/process.c
> > > @@ -720,7 +720,7 @@ void arch_cpu_idle_dead(void)
> > > /*
> > > * Called from the generic idle code.
> > > */
> > > -void arch_cpu_idle(void)
> > > +void noinstr arch_cpu_idle(void)
> > > {
> > > x86_idle();
> > > }
> > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > > index a4b8189455d5..20d529722f51 100644
> > > --- a/kernel/rcu/tree.c
> > > +++ b/kernel/rcu/tree.c
> > > @@ -896,7 +896,7 @@ static void noinstr rcu_eqs_exit(bool user)
> > > * If you add or remove a call to rcu_idle_exit(), be sure to test with
> > > * CONFIG_RCU_EQS_DEBUG=y.
> > > */
> > > -void rcu_idle_exit(void)
> > > +void noinstr rcu_idle_exit(void)
> > > {
> > > unsigned long flags;
> > >
> > > --
> > > 2.35.3
> > >
next prev parent reply other threads:[~2022-05-16 13:39 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-15 20:36 [PATCH bpf-next 1/2] cpuidle/rcu: Making arch_cpu_idle and rcu_idle_exit noinstr Jiri Olsa
2022-05-15 20:36 ` [PATCH bpf-next 2/2] selftests/bpf: Remove filter for unsafe functions in kprobe_multi test Jiri Olsa
2022-05-16 4:25 ` [PATCH bpf-next 1/2] cpuidle/rcu: Making arch_cpu_idle and rcu_idle_exit noinstr Paul E. McKenney
2022-05-16 11:49 ` Frederic Weisbecker
2022-05-16 13:39 ` Paul E. McKenney [this message]
2022-05-17 10:13 ` Jiri Olsa
2022-05-18 16:21 ` Paul E. McKenney
2022-05-19 11:33 ` Jiri Olsa
2022-05-19 13:54 ` Paul E. McKenney
2022-05-23 13:12 ` Jiri Olsa
2022-05-24 17:33 ` Paul E. McKenney
2022-05-17 2:39 ` kernel test robot
2022-05-17 2:54 ` Yonghong Song
2022-05-17 7:49 ` Jiri Olsa
2022-05-19 0:00 ` Masami Hiramatsu
2022-05-17 9:19 ` kernel test robot
2023-05-20 9:47 ` Ze Gao
2023-05-21 3:58 ` Yonghong Song
2023-05-21 15:10 ` Re: Ze Gao
2023-05-21 20:26 ` Re: Jiri Olsa
2023-05-22 1:36 ` Re: Masami Hiramatsu
2023-05-22 2:07 ` Re: Ze Gao
2023-05-23 4:38 ` Re: Yonghong Song
2023-05-23 5:30 ` Re: Masami Hiramatsu
2023-05-23 6:59 ` Re: Paul E. McKenney
2023-05-25 0:13 ` Re: Masami Hiramatsu
2023-05-23 14:10 ` kprobes and rcu_is_watching() Steven Rostedt
2023-05-24 3:51 ` Ze Gao
2023-05-21 8:08 ` Jiri Olsa
2023-05-21 10:09 ` Re: Masami Hiramatsu
2023-05-21 14:19 ` Re: Ze Gao
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