linux-kernel - Re: [PATCH/RFC] signal: Export signal_wake_up

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Date:   Sun, 7 May 2017 11:47:59 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-spi <linux-spi@...r.kernel.org>
Subject: Re: [PATCH/RFC] signal: Export signal_wake_up_state() to modules

Hi Oleg,

On Sat, May 6, 2017 at 9:42 PM, Oleg Nesterov <oleg@...hat.com> wrote:
> On 05/05, Geert Uytterhoeven wrote:
>> I'm using signal_wake_up() to abort a task blocked on
>> wait_for_completion_interruptible(), cfr. sh_msiof_slave_abort() in
>> "spi: sh-msiof: Add slave mode support"
>> (http://www.spinics.net/lists/devicetree/msg175575.html).
>>
>> Is exporting signal_wake_up_state() an acceptable solution?
>> Alternatively, I can extract the code to abort an completion into a
>> generic abort_completion() function, and export that.
>
> I too do not think this is a good idea... signal_wake_up() or even
> set_tsk_thread_flag() should never be used unless you actually send a
> signal. Yes, freeze_task() does this too but note that recalc_sigpending()
> checks freezing() and in this case we really want the target to enter the
> get_signal() path.
>
> And in fact I do not really understand why do you need it, it seems that
> you can easily rework this code and avoid this hack.

You mean having my own aborted flag, and calling complete_all()?

> Not to mention that sh_msiof_slave_abort() plays with struct completion
> internals, this doesn't look good too.

One reason to turn it into a generic abort_completion() function...

> Finally, clear_thread_flag(TIF_SIGPENDING) in sh_msiof_wait_for_completion()
> looks wrong. Or it is only for kthreads?

If I don't clear that flag, the next (by the same thread[*])
wait_for_completion_interruptible() will abort immediately.

[*] Typically this is the spi message pump worker.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds