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Date:   Thu, 9 Jun 2022 14:27:11 +0200
From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
To:     Dmitry Vyukov <dvyukov@google.com>
Cc:     John Ogness <john.ogness@linutronix.de>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Petr Mladek <pmladek@suse.com>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "open list:ARM/Amlogic Meson..." <linux-amlogic@lists.infradead.org>,
        Theodore Ts'o <tytso@mit.edu>,
        Alexander Potapenko <glider@google.com>,
        Marco Elver <elver@google.com>, kasan-dev@googlegroups.com,
        bigeasy@linutronix.de
Subject: Re: [PATCH printk v5 1/1] printk: extend console_lock for
 per-console locking
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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