linux-kernel - Re: [PATCH] printk/nmi: restore printk_func in nmi

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Message-ID: <20160301110528.GO3305@pathway.suse.cz>
Date:	Tue, 1 Mar 2016 12:05:29 +0100
From:	Petr Mladek <pmladek@...e.com>
To:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, Jan Kara <jack@...e.cz>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCH] printk/nmi: restore printk_func in nmi_panic

On Tue 2016-03-01 18:24:26, Sergey Senozhatsky wrote:
> Hello,
> 
> On (02/29/16 20:19), Sergey Senozhatsky wrote:
> [..]
> > > That is the problem. zap_locks() is not a solution.
> > > 
> > > First, it handles only lockbuf_lock and console_sem. There are other
> > > locks used by particular consoles that might cause a deadlock.
> > 
> > yes, well, that's true for panic() in general.
> 
> Petr, what do you think of this (added PRINTK_NMI_FLUSH_ON_PANIC)?
> 
> 1) zap_locks() in console_flush_on_panic()
> 2) add PRINTK_NMI_FLUSH_ON_PANIC symbols
> 3) add printk_nmi_flush_on_panic()

This is definitely better than nothing. Well, it seems that
the printk/NMI patches that motivated this patch will be
removed for a while, see
http://thread.gmane.org/gmane.linux.ports.arm.kernel/482845/focus=483002

I want to play with the panic handling a bit more and make it better
working out of box. It might be enough to put the messages into
the rind buffer when crashdump is going to be produced. Also
there is still the idea about using the lock-less early console.
I think that the solution from this patch might be the last
fallback.

Thanks a lot for proposals,
Petr