linux-kernel - Re: [PATCH RFC v5 3/6] srcu: Add notrace variant of srcu

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Message-ID: <CAJWu+oprTcnEhDprzaRmaO3-fyJ8vsdZP+ceNAEg2TqK-ZXwQA@mail.gmail.com>
Date:   Tue, 01 May 2018 15:07:01 +0000
From:   Joel Fernandes <joelaf@...gle.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Tom Zanussi <tom.zanussi@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Boqun Feng <boqun.feng@...il.com>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        "Cc: Frederic Weisbecker" <fweisbec@...il.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Fenguang Wu <fengguang.wu@...el.com>,
        Baohong Liu <baohong.liu@...el.com>,
        Vedang Patel <vedang.patel@...el.com>,
        "Cc: Android Kernel" <kernel-team@...roid.com>
Subject: Re: [PATCH RFC v5 3/6] srcu: Add notrace variant of srcu_dereference

On Tue, May 1, 2018 at 7:06 AM Steven Rostedt <rostedt@...dmis.org> wrote:

> On Mon, 30 Apr 2018 18:42:01 -0700
> Joel Fernandes <joelaf@...gle.com> wrote:

> > In this series, we are making lockdep use an rcuidle tracepoint. For
> > this reason we need a notrace variant of srcu_dereference since
> > otherwise we get lockdep splats since lockdep hooks may not have run
> > yet. This patch adds the needed variant.

> This change log is rather confusing. Why would lockdep use an rcuidle
> tracepoint? I think we need to explain more here.

Patch 6/6 registers lockdep onto irq_disable and irq_enable tracepoints
which use rcuidle:
https://github.com/torvalds/linux/blob/master/kernel/trace/trace_irqsoff.c#L791

I can add more details to the change log about this.

thanks,

- Joel