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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:     Petr Mladek <pmladek@suse.com>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        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: <YfER7tlXZZpX94c9@google.com>
References: <20220121190222.572694-1-stephen.s.brennan@oracle.com>
 <20220121190222.572694-3-stephen.s.brennan@oracle.com>
 <YfER7tlXZZpX94c9@google.com>
Date:   Wed, 26 Jan 2022 10:51:22 +0106
Message-ID: <87r18un83x.fsf@jogness.linutronix.de>
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> Is there something that prevents panic CPU from NMI hlt CPU which is
> in console_trylock() under raw_spin_lock_irqsave()?
>
>  CPU0				CPU1
> 				console_trylock_spinnning()
> 				 console_trylock()
> 				  down_trylock()
> 				   raw_spin_lock_irqsave(&sem->lock)
>
>  panic()
>   crash_smp_send_stop()
>    NMI 			-> 		HALT

This is a good point. I wonder if console_flush_on_panic() should
perform a sema_init() before it does console_trylock().

John