linux-kernel - Re: [PATCH v4 03/27] x86/entry: Flip _TIF_SIGPENDING and _TIF_NOTIFY

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Date:   Fri, 21 Feb 2020 17:14:45 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        rostedt@...dmis.org
Cc:     mingo@...nel.org, joel@...lfernandes.org,
        gregkh@...uxfoundation.org, gustavo@...eddedor.com,
        tglx@...utronix.de, paulmck@...nel.org, josh@...htriplett.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        luto@...nel.org, tony.luck@...el.com, frederic@...nel.org,
        dan.carpenter@...cle.com, mhiramat@...nel.org
Subject: Re: [PATCH v4 03/27] x86/entry: Flip _TIF_SIGPENDING and
 _TIF_NOTIFY_RESUME handling

On Fri, Feb 21, 2020 at 02:34:19PM +0100, Peter Zijlstra wrote:
> Make sure we run task_work before we hit any kind of userspace -- very
> much including signals.
> 
> Suggested-by: Andy Lutomirski <luto@...nel.org>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  arch/x86/entry/common.c                   |    8 
>  usr/src/linux-2.6/arch/x86/entry/common.c |  440 ------------------------------
>  2 files changed, 4 insertions(+), 444 deletions(-)
> 
> --- a/arch/x86/entry/common.c
> +++ b/arch/x86/entry/common.c
> @@ -155,16 +155,16 @@ static void exit_to_usermode_loop(struct
>  		if (cached_flags & _TIF_PATCH_PENDING)
>  			klp_update_patch_state(current);
>  
> -		/* 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);
>  		}
>  
> +		/* deal with pending signal delivery */
> +		if (cached_flags & _TIF_SIGPENDING)
> +			do_signal(regs);
> +

For giggles, I just found:

	do_signal()
	  get_signal()
	    task_work_run()