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From:   John Ogness <john.ogness@linutronix.de>
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To:     Sergey Senozhatsky <senozhatsky@chromium.org>,
        Stephen Brennan <stephen.s.brennan@oracle.com>
Cc:     Sergey Senozhatsky <senozhatsky@chromium.org>,
        Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/4] printk: disable optimistic spin during panic
In-Reply-To: <YfJFjHdg/khNXiRd@google.com>
References: <20220121190222.572694-1-stephen.s.brennan@oracle.com>
 <20220121190222.572694-3-stephen.s.brennan@oracle.com>
 <YfER7tlXZZpX94c9@google.com> <87r18un83x.fsf@jogness.linutronix.de>
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 <YfJFjHdg/khNXiRd@google.com>
Date:   Thu, 27 Jan 2022 10:15:05 +0106
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On 2022-01-27, Sergey Senozhatsky <senozhatsky@chromium.org> wrote:
> Right. So I also thought about placing panic_in_progress() somewhere in
> console_trylock() and make it fail for anything that is not a panic
> CPU.

I think this is a good idea and console_trylock() is the correct place
for that.

> Back in the days we also had this idea of "detaching" non-panic CPUs from
> printk() by overwriting their printk function pointers.

We need to keep in mind that printk() is no longer the problem. The
records are stored locklessly. The problem is the
console_trylock()/console_unlock() within vprintk_emit(). IMHO adding a
panic check in console_trylock() should solve that race sufficiently.

John