From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E7443C10DCE for ; Fri, 6 Mar 2020 15:51:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B2E292072A for ; Fri, 6 Mar 2020 15:51:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="XfZXnAg7" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727075AbgCFPvd (ORCPT ); Fri, 6 Mar 2020 10:51:33 -0500 Received: from mail-lf1-f66.google.com ([209.85.167.66]:33655 "EHLO mail-lf1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726231AbgCFPvd (ORCPT ); Fri, 6 Mar 2020 10:51:33 -0500 Received: by mail-lf1-f66.google.com with SMTP id c20so2327149lfb.0; Fri, 06 Mar 2020 07:51:31 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=8vpKlxC6kfx/8ZEoHOV/lRWNX/tTNmbczPd46/3sqEc=; b=XfZXnAg7SpiORK5atXAtoAXdiyl4DfgFaVoB3ydY3ygwtW/387vVOoRgbZxbZKfKwM 8oaCjXWru31WY0xBI/QcCXiTAAHefK6flvHQjYNLRgwiesTKIGV5X1DoOcoH5wZoef/L u2+e8YzvBan6Ow4VBp2EnkcyF4f+G/mZkJVcJLPO4eZdgUMEQbDlSnkRw/zuFO1FdSNs U5X1JOpCD341/wcHPOXwpLOK2eWeTcAaXOmqMk73kr9mSq8dmMQq3iJOO41r0ReUWzMS rsS76vv67abvaAZ+0rsAOJVsfKpCuqLJ4aLC3gJMagKwEdxkTQE1+dpJrWX7OKk5EOwQ 0lTA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=8vpKlxC6kfx/8ZEoHOV/lRWNX/tTNmbczPd46/3sqEc=; b=IaJb2G0S42j+TacYRP++EZMoXUjIFIsIUtVnRU5XhV7PnumRAG3yxeLKoLJzDCBGqH vTdQn+NtFeMX67X0GK65wufAITBVEAG5TYQUbfvwIUQxV+a26exPsXuyLp0RrZ9IOE+d Z9Yvu5AbYbcIa4D+xNh9HWylSIStVYQXdTW0DUKl3MiRzoa76AuBRpHA3DuhKSJdFuxT Uz3Xz/MWOsmMBcf/T6Kjjn9tAi0XMXrsOop08S2VGa49XItB6JIBU4nifak1iNJfIkou 7kE4jpXLrjSSk1gpzeXbkieNrZnXlDAbNCl6xEcgf2ZC+S/Lnx5lpDfKLqrQ1XLswPkk sg4A== X-Gm-Message-State: ANhLgQ38uf5wZaj2+DerzQjKU+mwmAm3qnuVRLyCjVwUS6tViXfT01rq IKbHjh3SEkw07i9w3ZKTeD6rZKJK04ac8CjQGqM= X-Google-Smtp-Source: ADFU+vtn69XZXX/kFdXPbs7zor1IlvqpO+zLZqcQapmofU9e5T2kEJcKuCgrhX4rG3PpRoGnbpNhkP8BA+n03ocZc5A= X-Received: by 2002:ac2:4647:: with SMTP id s7mr2314121lfo.73.1583509890293; Fri, 06 Mar 2020 07:51:30 -0800 (PST) MIME-Version: 1.0 References: <20200221133416.777099322@infradead.org> <20200221134216.051596115@infradead.org> <20200306104335.GF3348@worktop.programming.kicks-ass.net> <20200306113135.GA8787@worktop.programming.kicks-ass.net> In-Reply-To: <20200306113135.GA8787@worktop.programming.kicks-ass.net> From: Alexei Starovoitov Date: Fri, 6 Mar 2020 07:51:18 -0800 Message-ID: Subject: Re: [PATCH v4 16/27] tracing: Remove regular RCU context for _rcuidle tracepoints (again) To: Peter Zijlstra Cc: LKML , linux-arch , Steven Rostedt , Ingo Molnar , Joel Fernandes , Greg Kroah-Hartman , "Gustavo A. R. Silva" , Thomas Gleixner , "Paul E. McKenney" , Josh Triplett , Mathieu Desnoyers , jiangshanlai@gmail.com, Andy Lutomirski , Tony Luck , Frederic Weisbecker , Dan Carpenter , Masami Hiramatsu Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 6, 2020 at 3:31 AM Peter Zijlstra 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) > > > Reviewed-by: Steven Rostedt (VMware) > > > --- > > > 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.