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 18:39:47 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        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>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [patch V4 part 1 29/36] x86/mce: Send #MC singal from task work

On Thu, May 14, 2020 at 12:03:30PM -0400, Mathieu Desnoyers wrote:
> - #MC triggered, queuing task work,
> - unrelated signal happens to be delivered to task,
> - exit to usermode loop handles do_signal first,
> - then it runs task work.

How can that even happen?

exit_to_usermode_loop->do_signal->get_signal and that does:

        if (unlikely(current->task_works))
                task_work_run();

at the top.

So the task work will always run before the signal handler.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette