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From:   John Ogness <john.ogness@linutronix.de>
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To:     Stephen Brennan <stephen.s.brennan@oracle.com>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        Petr Mladek <pmladek@suse.com>
Cc:     Arnd Bergmann <arnd@arndb.de>,
        Steven Rostedt <rostedt@goodmis.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Stephen Brennan <stephen.s.brennan@oracle.com>,
        Sebastian Reichel <sre@kernel.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 4/4] printk: Drop console_sem during panic
In-Reply-To: <20220126230236.750229-5-stephen.s.brennan@oracle.com>
References: <20220126230236.750229-1-stephen.s.brennan@oracle.com>
 <20220126230236.750229-5-stephen.s.brennan@oracle.com>
Date:   Thu, 27 Jan 2022 10:28:53 +0106
Message-ID: <87fsp9pm6q.fsf@jogness.linutronix.de>
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On 2022-01-26, Stephen Brennan <stephen.s.brennan@oracle.com> wrote:
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -2759,7 +2782,7 @@ void console_unlock(void)
>  	 * flush, no worries.
>  	 */
>  	retry = prb_read_valid(prb, next_seq, NULL);
> -	if (retry && console_trylock())
> +	if (retry && !abandon_console_lock_in_panic() && console_trylock())

As Sergey suggested [0], I would like to see the call to
abandon_console_lock_in_panic() move inside console_trylock(). This will
help to avoid the race between NMI CPU halt and the internal sema.lock
spinlock.

John Ogness

[0] https://lore.kernel.org/all/YfJFjHdg%2FkhNXiRd@google.com