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

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Message-ID: <20170506194256.GA21726@redhat.com>
Date:   Sat, 6 May 2017 21:42:56 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Geert Uytterhoeven <geert+renesas@...der.be>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org
Subject: Re: [PATCH/RFC] signal: Export signal_wake_up_state() to modules

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.

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

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

Oleg.