linux-kernel - Re: [PATCH v5 4/4] printk/nmi: flush NMI messages on the system panic

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Date:	Tue, 26 Apr 2016 16:21:57 +0200
From:	Petr Mladek <pmladek@...e.com>
To:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Daniel Thompson <daniel.thompson@...aro.org>,
	Jiri Kosina <jkosina@...e.com>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Chris Metcalf <cmetcalf@...hip.com>,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	linux-arm-kernel@...ts.infradead.org,
	adi-buildroot-devel@...ts.sourceforge.net,
	linux-cris-kernel@...s.com, linux-mips@...ux-mips.org,
	linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
	linux-sh@...r.kernel.org, sparclinux@...r.kernel.org
Subject: Re: [PATCH v5 4/4] printk/nmi: flush NMI messages on the system panic

On Sat 2016-04-23 12:49:24, Sergey Senozhatsky wrote:
> Hello Petr,
> 
> On (04/21/16 13:48), Petr Mladek wrote:
> >  extern void printk_nmi_flush(void);
> > +extern void printk_nmi_flush_on_panic(void);
> >  #else
> >  static inline void printk_nmi_flush(void) { }
> > +static inline void printk_nmi_flush_on_panic(void) { }
> [..]
> > +void printk_nmi_flush_on_panic(void)
> > +{
> > +	/*
> > +	 * Make sure that we could access the main ring buffer.
> > +	 * Do not risk a double release when more CPUs are up.
> > +	 */
> > +	if (in_nmi() && raw_spin_is_locked(&logbuf_lock)) {
> > +		if (num_online_cpus() > 1)
> > +			return;
> > +
> > +		debug_locks_off();
> > +		raw_spin_lock_init(&logbuf_lock);
> > +	}
> > +
> > +	printk_nmi_flush();
> > +}
> [..]
> > -static DEFINE_RAW_SPINLOCK(logbuf_lock);
> > +DEFINE_RAW_SPINLOCK(logbuf_lock);
> 
> just an idea,
> 
> how about doing it a bit differently?
> 
> 
> move printk_nmi_flush_on_panic() to printk.c, and place it next to
> printk_flush_on_panic() (so we will have two printk "flush-on-panic"
> functions sitting together). /* printk_nmi_flush() is in printk.h,
> so it's visible to printk anyway */
> 
> it also will let us keep logbuf_lock static, it's a bit too internal
> to printk to expose it, I think.
> 
> IOW, something like this?

It is rather cosmetic change. I 

> ---
> 
>  kernel/printk/internal.h |  2 --
>  kernel/printk/nmi.c      | 27 ---------------------------
>  kernel/printk/printk.c   | 29 ++++++++++++++++++++++++++++-
>  3 files changed, 28 insertions(+), 30 deletions(-)
> 
> diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
> index 7fd2838..341bedc 100644
> --- a/kernel/printk/internal.h
> +++ b/kernel/printk/internal.h
> @@ -22,8 +22,6 @@ int __printf(1, 0) vprintk_default(const char *fmt, va_list args);
>  
>  #ifdef CONFIG_PRINTK_NMI
>  
> -extern raw_spinlock_t logbuf_lock;

Well, it was exposed only in the internal.h header file. I consider
this rather a cosmetic change and do not have strong opinion about it. :-)

Anyway, thanks a lot for review.

Best Regards,
Petr