linux-kernel - Re: [patch V4 part 1 29/36] x86/mce: Send #MC singal from task work

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Message-ID: <87y2puxvqa.fsf@nanos.tec.linutronix.de>
Date:   Thu, 14 May 2020 19:38:37 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>,
        paulmck <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>, rostedt <rostedt@...dmis.org>,
        "Joel Fernandes\, Google" <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [patch V4 part 1 29/36] x86/mce: Send #MC singal from task work

Mathieu Desnoyers <mathieu.desnoyers@...icios.com> writes:
> ----- On May 5, 2020, at 9:16 AM, Thomas Gleixner tglx@...utronix.de wrote:
>
>> From: Peter Zijlstra <peterz@...radead.org>
>> 
>
> Patch title: singal -> signal.
>
>> Convert #MC over to using task_work_add(); it will run the same code
>> slightly later, on the return to user path of the same exception.
>
> So I suspect that switching the order between tracehook_notify_resume()
> (which ends up calling task_work_run()) and do_signal() done by an
> earlier patch in this series intends to ensure the information about the
> instruction pointer causing the #MC is not overwritten by do_signal()
> (but I'm just guessing).

No, it does not. See the ordering discussion.

Aside of that signal never transported any address information. It uses
force_sig(SIGBUS).

Even if a different signal would be sent first then the register frame
of the #MC is still there when the fatal signal is sent later.

But even w/o changing the ordering the taskwork check in do_signal()
runs the pending work before delivering anything.

Thanks,

        tglx