linux-kernel - Re: [PATCH v3 02/22] x86,mce: Delete ist_begin_non

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Message-ID: <20200219174223.GE30966@zn.tnic>
Date:   Wed, 19 Feb 2020 18:42:23 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Greg KH <gregkh@...uxfoundation.org>, gustavo@...eddedor.com,
        Thomas Gleixner <tglx@...utronix.de>, paulmck@...nel.org,
        Josh Triplett <josh@...htriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Tony Luck <tony.luck@...el.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH v3 02/22] x86,mce: Delete ist_begin_non_atomic()

On Wed, Feb 19, 2020 at 09:21:48AM -0800, Andy Lutomirski wrote:
> Unless there is a signal pending and the signal setup code is about to
> hit the same failed memory.  I suppose we can just treat cases like
> this as "oh well, time to kill the whole system".
>
> But we should genuinely agree that we're okay with deferring this handling.

Good catch!

static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
{

	...

		/* deal with pending signal delivery */
                if (cached_flags & _TIF_SIGPENDING)
                        do_signal(regs);

                if (cached_flags & _TIF_NOTIFY_RESUME) {
                        clear_thread_flag(TIF_NOTIFY_RESUME);
                        tracehook_notify_resume(regs);
                        rseq_handle_notify_resume(NULL, regs);
                }


Err, can we make task_work run before we handle signals? Or there's a
reason it is run in this order?

Comment over task_work_add() says:

 * This is like the signal handler which runs in kernel mode, but it doesn't
 * try to wake up the @task.

which sounds to me like this should really run before the signal
handlers...

-- 
Regards/Gruss,
    Boris.

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