linux-kernel - Re: [PATCH printk v2 2/5] printk: Add NMI safety to console_flush_on_panic() and console

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Message-ID: <20230714040049.GA81525@google.com>
Date:   Fri, 14 Jul 2023 13:00:49 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     John Ogness <john.ogness@...utronix.de>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH printk v2 2/5] printk: Add NMI safety to
 console_flush_on_panic() and console_unblank()

On (23/07/13 16:43), Petr Mladek wrote:
> 
> Simple removal of console_trylock() in console_flush_on_panic() would
> cause that other CPUs might still be able to take it and race.
> The problem is avoided by checking panic_in_progress() in console_lock()
> and console_trylock(). They will never succeed on non-panic CPUs.
> 

In theory, we also can have non-panic CPU in console_flush_all(),
which should let panic CPU to take over the next time it checks
abandon_console_lock_in_panic() (other_cpu_in_panic() after 5/5),
but it may not happen immediately. I wonder if we somehow can/want
to "wait" in console_flush_on_panic() for non-panic CPU handover?