From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
linux-arch <linux-arch@vger.kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Ingo Molnar <mingo@kernel.org>,
Joel Fernandes <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>,
jiangshanlai@gmail.com, Andy Lutomirski <luto@kernel.org>,
Tony Luck <tony.luck@intel.com>,
Frederic Weisbecker <frederic@kernel.org>,
Dan Carpenter <dan.carpenter@oracle.com>,
Masami Hiramatsu <mhiramat@kernel.org>
Subject: Re: [PATCH v4 16/27] tracing: Remove regular RCU context for _rcuidle tracepoints (again)
Date: Fri, 6 Mar 2020 07:51:18 -0800 [thread overview]
Message-ID: <CAADnVQKp=UKg8HAuMOFknhmXtfm_LVu_ynTNJuedHqKdA6zh1g@mail.gmail.com> (raw)
In-Reply-To: <20200306113135.GA8787@worktop.programming.kicks-ass.net>
On Fri, Mar 6, 2020 at 3:31 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Fri, Mar 06, 2020 at 11:43:35AM +0100, Peter Zijlstra wrote:
> > On Fri, Feb 21, 2020 at 02:34:32PM +0100, Peter Zijlstra wrote:
> > > Effectively revert commit 865e63b04e9b2 ("tracing: Add back in
> > > rcu_irq_enter/exit_irqson() for rcuidle tracepoints") now that we've
> > > taught perf how to deal with not having an RCU context provided.
> > >
> > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > > Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
> > > ---
> > > include/linux/tracepoint.h | 8 ++------
> > > 1 file changed, 2 insertions(+), 6 deletions(-)
> > >
> > > --- a/include/linux/tracepoint.h
> > > +++ b/include/linux/tracepoint.h
> > > @@ -179,10 +179,8 @@ static inline struct tracepoint *tracepo
> > > * For rcuidle callers, use srcu since sched-rcu \
> > > * doesn't work from the idle path. \
> > > */ \
> > > - if (rcuidle) { \
> > > + if (rcuidle) \
> > > __idx = srcu_read_lock_notrace(&tracepoint_srcu);\
> > > - rcu_irq_enter_irqsave(); \
> > > - } \
> > > \
> > > it_func_ptr = rcu_dereference_raw((tp)->funcs); \
> > > \
> > > @@ -194,10 +192,8 @@ static inline struct tracepoint *tracepo
> > > } while ((++it_func_ptr)->func); \
> > > } \
> > > \
> > > - if (rcuidle) { \
> > > - rcu_irq_exit_irqsave(); \
> > > + if (rcuidle) \
> > > srcu_read_unlock_notrace(&tracepoint_srcu, __idx);\
> > > - } \
> > > \
> > > preempt_enable_notrace(); \
> > > } while (0)
> >
> > So what happens when BPF registers for these tracepoints? BPF very much
> > wants RCU on AFAIU.
>
> I suspect we needs something like this...
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index a2f15222f205..67a39dbce0ce 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -1475,11 +1475,13 @@ void bpf_put_raw_tracepoint(struct bpf_raw_event_map *btp)
> static __always_inline
> void __bpf_trace_run(struct bpf_prog *prog, u64 *args)
> {
> + int rcu_flags = trace_rcu_enter();
> rcu_read_lock();
> preempt_disable();
> (void) BPF_PROG_RUN(prog, args);
> preempt_enable();
> rcu_read_unlock();
> + trace_rcu_exit(rcu_flags);
One big NACK.
I will not slowdown 99% of cases because of one dumb user.
Absolutely no way.
next prev parent reply other threads:[~2020-03-06 15:51 UTC|newest]
Thread overview: 84+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-21 13:34 [PATCH v4 00/27] tracing vs world Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 01/27] lockdep: Teach lockdep about "USED" <- "IN-NMI" inversions Peter Zijlstra
2020-02-21 15:08 ` Steven Rostedt
2020-02-21 20:25 ` Peter Zijlstra
2020-02-21 20:28 ` Steven Rostedt
2020-02-21 22:01 ` Frederic Weisbecker
2020-02-22 3:08 ` Joel Fernandes
2020-02-24 10:10 ` Peter Zijlstra
2020-02-25 2:12 ` Joel Fernandes
2020-03-20 12:58 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 02/27] hardirq/nmi: Allow nested nmi_enter() Peter Zijlstra
2020-02-21 22:21 ` Frederic Weisbecker
2020-02-24 12:13 ` Petr Mladek
2020-02-25 1:30 ` Frederic Weisbecker
2020-02-24 16:13 ` Peter Zijlstra
2020-02-25 3:09 ` Frederic Weisbecker
2020-02-25 15:41 ` Peter Zijlstra
2020-02-25 16:21 ` Frederic Weisbecker
2020-02-25 22:10 ` Frederic Weisbecker
2020-02-27 9:10 ` Peter Zijlstra
2020-02-27 13:34 ` Frederic Weisbecker
2020-02-21 13:34 ` [PATCH v4 03/27] x86/entry: Flip _TIF_SIGPENDING and _TIF_NOTIFY_RESUME handling Peter Zijlstra
2020-02-21 16:14 ` Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 04/27] x86/mce: Delete ist_begin_non_atomic() Peter Zijlstra
2020-02-21 19:07 ` Andy Lutomirski
2020-02-21 23:40 ` Frederic Weisbecker
2020-02-21 13:34 ` [PATCH v4 05/27] x86: Replace ist_enter() with nmi_enter() Peter Zijlstra
2020-02-21 19:05 ` Andy Lutomirski
2020-02-21 20:22 ` Peter Zijlstra
2020-02-24 10:43 ` Peter Zijlstra
2020-02-24 16:27 ` Steven Rostedt
2020-02-24 16:34 ` Peter Zijlstra
2020-02-24 16:47 ` Steven Rostedt
2020-02-24 21:31 ` Peter Zijlstra
2020-02-24 22:02 ` Steven Rostedt
2020-02-26 10:25 ` Peter Zijlstra
2020-02-26 13:16 ` Peter Zijlstra
2020-02-26 10:27 ` Peter Zijlstra
2020-02-26 15:20 ` Steven Rostedt
2020-03-07 1:53 ` Masami Hiramatsu
2020-02-21 13:34 ` [PATCH v4 06/27] x86/doublefault: Remove memmove() call Peter Zijlstra
2020-02-21 19:10 ` Andy Lutomirski
2020-02-21 13:34 ` [PATCH v4 07/27] rcu: Make RCU IRQ enter/exit functions rely on in_nmi() Peter Zijlstra
2020-02-26 0:23 ` Frederic Weisbecker
2020-02-21 13:34 ` [PATCH v4 08/27] rcu/kprobes: Comment why rcu_nmi_enter() is marked NOKPROBE Peter Zijlstra
2020-02-26 0:27 ` Frederic Weisbecker
2020-02-21 13:34 ` [PATCH v4 09/27] rcu: Rename rcu_irq_{enter,exit}_irqson() Peter Zijlstra
2020-02-21 20:21 ` Steven Rostedt
2020-02-24 10:24 ` Peter Zijlstra
2020-02-26 0:35 ` Frederic Weisbecker
2020-02-21 13:34 ` [PATCH v4 10/27] rcu: Mark rcu_dynticks_curr_cpu_in_eqs() inline Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 11/27] rcu,tracing: Create trace_rcu_{enter,exit}() Peter Zijlstra
2020-03-06 11:50 ` Peter Zijlstra
2020-03-06 12:40 ` Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 12/27] sched,rcu,tracing: Avoid tracing before in_nmi() is correct Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 13/27] x86,tracing: Add comments to do_nmi() Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 14/27] perf,tracing: Prepare the perf-trace interface for RCU changes Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 15/27] tracing: Employ trace_rcu_{enter,exit}() Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 16/27] tracing: Remove regular RCU context for _rcuidle tracepoints (again) Peter Zijlstra
2020-03-06 10:43 ` Peter Zijlstra
2020-03-06 11:31 ` Peter Zijlstra
2020-03-06 15:51 ` Alexei Starovoitov [this message]
2020-03-06 16:04 ` Mathieu Desnoyers
2020-03-06 17:55 ` Steven Rostedt
2020-03-06 18:45 ` Joel Fernandes
2020-03-06 18:59 ` Steven Rostedt
2020-03-06 19:14 ` Joel Fernandes
2020-03-06 20:22 ` Mathieu Desnoyers
2020-03-06 20:45 ` Steven Rostedt
2020-03-06 20:55 ` Mathieu Desnoyers
2020-03-06 21:06 ` Steven Rostedt
2020-03-06 23:10 ` Alexei Starovoitov
2020-03-06 17:21 ` Joel Fernandes
2020-02-21 13:34 ` [PATCH v4 17/27] perf,tracing: Allow function tracing when !RCU Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 18/27] x86/int3: Ensure that poke_int3_handler() is not traced Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 19/27] locking/atomics, kcsan: Add KCSAN instrumentation Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 20/27] asm-generic/atomic: Use __always_inline for pure wrappers Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 21/27] asm-generic/atomic: Use __always_inline for fallback wrappers Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 22/27] compiler: Simple READ/WRITE_ONCE() implementations Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 23/27] locking/atomics: Flip fallbacks and instrumentation Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 24/27] x86/int3: Avoid atomic instrumentation Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 25/27] lib/bsearch: Provide __always_inline variant Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 26/27] x86/int3: Inline bsearch() Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 27/27] x86/int3: Ensure that poke_int3_handler() is not sanitized Peter Zijlstra
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