linux-kernel - Re: [patch V4 part 1 22/36] tracing: Provide lockdep less trace_hardirqs

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Message-ID: <CALCETrU7rf8cizYM1v0Rb6LzufLEbNcAS6Ebx_BW=+3Svk+F2g@mail.gmail.com>
Date:   Thu, 7 May 2020 10:55:47 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>
Subject: Re: [patch V4 part 1 22/36] tracing: Provide lockdep less
 trace_hardirqs_on/off() variants

On Tue, May 5, 2020 at 7:13 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> trace_hardirqs_on/off() is only partially safe vs. RCU idle. The tracer
> core itself is safe, but the resulting tracepoints can be utilized by
> e.g. BPF which is unsafe.
>
> Provide variants which do not contain the lockdep invocation so the lockdep
> and tracer invocations can be split at the call site and placed properly.
>
> The new variants also do not use rcuidle as they are going to be called
> from entry code after/before context tracking.

I can't quite follow this.  Are you saying that the new variants are
intended to be called by the entry code in a context where tracing is
acceptable and that the lockdep part will still be called in a context
where tracing is not acceptable?

--Andy