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Date: Sat, 27 Feb 2016 12:33:41 +0900
From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Petr Mladek <pmladek@suse.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>, Jan Kara <jack@suse.cz>,
        Peter Zijlstra <peterz@infradead.org>,
        Steven Rostedt <rostedt@goodmis.org>, Ingo Molnar <mingo@redhat.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] printk/nmi: restore printk_func in nmi_panic
Message-ID: <20160227033341.GA396@swordfish>
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On (02/27/16 12:09), Sergey Senozhatsky wrote:
> On (02/27/16 11:19), Sergey Senozhatsky wrote:
> [..]
> > > I think about a compromise. We should try to get the messages
> > > out only when kdump is not enabled.
> > 
> > can we zap_locks() if we are on nmi_panic()->panic()->console_flush_on_panic() path?
> > console_flush_on_panic() is happening after we send out smp_send_stop().
> 
> can something like this do the trick?

hm, no. it can't.

I forgot to move printk_nmi_exit() from nmi_panic() to panic(). so
it should have been:

	panic()
		...
		printk_nmi_exit()
		console_flush_on_panic()
			__zap_locks()
			printk_nmi_flush()
			console_unlock()

but this __zap_locks() can _in theory_ race with irq_work->printk_nmi_flush().
so we need something more than this...

	-ss