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Date:   Tue, 22 Nov 2022 10:20:44 -0800
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     Petr Mladek <pmladek@suse.com>
Cc:     John Ogness <john.ogness@linutronix.de>,
        Naresh Kamboju <naresh.kamboju@linaro.org>,
        open list <linux-kernel@vger.kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Sergey Senozhatsky <senozhatsky@chromium.org>
Subject: Re: next-20221122: tinyconfig: ppc n s390:
 kernel/printk/printk.c:95:1: error: type specifier missing, defaults to
 'int'; ISO C99 and later do not support implicit int
 [-Werror,-Wimplicit-int]
Message-ID: <20221122182044.GN4001@paulmck-ThinkPad-P17-Gen-1>
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On Tue, Nov 22, 2022 at 04:55:26PM +0100, Petr Mladek wrote:
> On Tue 2022-11-22 16:33:39, John Ogness wrote:
> > On 2022-11-22, "Paul E. McKenney" <paulmck@kernel.org> wrote:
> > >> @paulmck: Do you have a problem with permanently activating CONFIG_SRCU?
> > >
> > > The people wanting it separate back in the day were those wanting very
> > > tiny kernels.  I have not heard from them in a long time, so maybe it
> > > is now OK to just make SRCU unconditional.
> > 
> > Who decides this? Or maybe I should create a semaphore-based Variant of
> > console_srcu_read_lock()/console_srcu_read_unlock() for the
> > "!CONFIG_PRINTK && !CONFIG_SRCU" case?
> 
> I would prefer to avoid it. It would require keeping this in mind.
> Semaphore behaves very differently than srcu_read_lock (deadlocks,
> nesting).
> 
> I am not sure how much the tiny SRCU would increase the size of
> the kernel. I doubt that it would be more that what printk()
> added by the various per-CPU and per-console buffers.
> 
> Well, another question is why we actually need to register the consoles
> at all for !CONFIG_PRINTK. Only reasons come to my mind:
> 
>    + /dev/console
>    + preventing double registration/unregistration (initialization)
> 
> I could imagine to handle these two use-cases a special way
> on tiny systems. But I would do it only when anyone complains.

Tiny SRCU is indeed tiny.

And given the large number of "select SRCU" statements out there,
I doubt that there are very many Linux kernels running in production
without SRCU.  Very likely none at all, actually.

I will put together a patch series.

							Thanx, Paul