linux-kernel - Re: [patch V4 part 2 06/18] x86/entry: Move irq flags tracing to prepare_exit_to

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Date:   Sat, 09 May 2020 12:16:07 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andy Lutomirski <luto@...nel.org>
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 2 06/18] x86/entry: Move irq flags tracing to prepare_exit_to_usermode()

Andy Lutomirski <luto@...nel.org> writes:
> On Tue, May 5, 2020 at 7:14 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>>
>> This is another step towards more C-code and less convoluted ASM.
>>
>> Similar to the entry path, invoke the tracer before context tracking which
>> might turn off RCU and invoke lockdep as the last step before going back to
>> user space. Annotate the code sections in exit_to_user_mode() accordingly
>> so objtool won't complain about the tracer invocation.
>
> Acked-by: Andy Lutomirski <luto@...nel.org>
>
> Note to self: the nmi code needs to be reworked to go through
> prepare_exit_to_usermode(), too.  I'll do this once this whole pile
> lands.

Why? NMI does not set any work stuff or preemption. If something needs
to be done then NMI raises irq_work which uses the regular path.

Thanks,

        tglx