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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc:     linux-kernel <linux-kernel@vger.kernel.org>, x86 <x86@kernel.org>,
        paulmck <paulmck@kernel.org>, Andy Lutomirski <luto@kernel.org>,
        Alexandre Chartre <alexandre.chartre@oracle.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Petr Mladek <pmladek@suse.com>, rostedt <rostedt@goodmis.org>,
        "Joel Fernandes\, Google" <joel@joelfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        Brian Gerst <brgerst@gmail.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Will Deacon <will@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: [patch V4 part 1 29/36] x86/mce: Send #MC singal from task work
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Date:   Thu, 14 May 2020 19:38:37 +0200
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Mathieu Desnoyers <mathieu.desnoyers@efficios.com> writes:
> ----- On May 5, 2020, at 9:16 AM, Thomas Gleixner tglx@linutronix.de wrote:
>
>> From: Peter Zijlstra <peterz@infradead.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