linux-kernel - Re: [PATCH printk v5 1/1] printk: extend console

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Date:   Thu, 9 Jun 2022 14:27:11 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     John Ogness <john.ogness@...utronix.de>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "open list:ARM/Amlogic Meson..." <linux-amlogic@...ts.infradead.org>,
        Theodore Ts'o <tytso@....edu>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>, kasan-dev@...glegroups.com,
        bigeasy@...utronix.de
Subject: Re: [PATCH printk v5 1/1] printk: extend console_lock for
 per-console locking

Hi Dmitry,

On Thu, Jun 09, 2022 at 02:18:19PM +0200, Dmitry Vyukov wrote:
> > AFAIK, CONFIG_PROVE_RAW_LOCK_NESTING is useful for teasing out cases
> > where RT's raw spinlocks will nest wrong with RT's sleeping spinlocks.
> > But nobody who wants an RT kernel will be using KFENCE. So this seems
> > like a non-issue? Maybe just add a `depends on !KFENCE` to
> > PROVE_RAW_LOCK_NESTING?
> 
> Don't know if there are other good solutions (of similar simplicity).

Fortunately, I found one that solves things without needing to
compromise on anything:
https://lore.kernel.org/lkml/20220609121709.12939-1-Jason@zx2c4.com/

> Btw, should this new CONFIG_PROVE_RAW_LOCK_NESTING be generally
> enabled on testing systems? We don't have it enabled on syzbot.

Last time I spoke with RT people about this, the goal was eventually to
*always* enable it when lock proving is enabled, but there are too many
bugs and cases now to do that, so it's an opt-in. I might be
misremembering, though, so CC'ing Sebastian in case he wants to chime
in.

Jason