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

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Date:   Thu, 14 May 2020 13:42:01 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Thomas Gleixner <tglx@...utronix.de>
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

----- On May 14, 2020, at 1:38 PM, Thomas Gleixner tglx@...utronix.de wrote:

> 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.

Yep, that was the key thing I missed,

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com