linux-kernel - Re: [PATCH v5 2/2] x86 mce: use new printk recursion disabling interface

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Date:	Wed, 06 Jun 2012 08:36:05 +0800
From:	Yanmin Zhang <yanmin_zhang@...ux.intel.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	ShuoX Liu <shuox.liu@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Luck, Tony" <tony.luck@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH v5 2/2] x86 mce: use new printk recursion disabling
 interface

On Tue, 2012-06-05 at 17:15 +0200, Borislav Petkov wrote:
> On Tue, Jun 05, 2012 at 05:55:22PM +0800, ShuoX Liu wrote:
> > From: ShuoX Liu <shuox.liu@...el.com>
> > 
> > On x86 machines, some times MCE happens just when kernel calls printk
> > to output some log info to serial console, while usually MCE module in
> > kernel is used to print out some hardware error information, such like
> > bad cache or bad memory bank. That causes printk recursion and printk
> > would omit MCE printk output.
> > 
> > We hit it when running MTBF testing on Android ATOM mobiles.
> > 
> > Here in mce_panic, we choose to disable printk recursion to make sure
> > MCE logs printed out.
> > 
> > Signed-off-by: Yanmin Zhang <yanmin_zhang@...ux.intel.com>
> > Signed-off-by: ShuoX Liu <shuox.liu@...el.com>
> > ---
> >  arch/x86/kernel/cpu/mcheck/mce.c |    2 ++
> >  1 files changed, 2 insertions(+), 0 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
> > index 2afcbd2..906e838 100644
> > --- a/arch/x86/kernel/cpu/mcheck/mce.c
> > +++ b/arch/x86/kernel/cpu/mcheck/mce.c
> > @@ -306,6 +306,7 @@ static void mce_panic(char *msg, struct mce *final, char *exp)
> >  {
> >  	int i, apei_err = 0;
> >  
> > +	printk_recursion_check_disable();
> >  	if (!fake_panic) {
> >  		/*
> >  		 * Make sure only one CPU runs in machine check panic
> > @@ -360,6 +361,7 @@ static void mce_panic(char *msg, struct mce *final, char *exp)
> >  		panic(msg);
> >  	} else
> >  		pr_emerg(HW_ERR "Fake kernel panic: %s\n", msg);
> > +	printk_recursion_check_enable();
> 
> Ok, let me ask this again: why not disable the printk recursion check in
> the function that actually _prints_ the MCE, i.e. print_mce() instead of
> here in mce_panic() which does a whole bunch of other stuff and it can
> also return without printing any MCE to dmesg?
Sorry for forgetting the return checking.

> Are you interested in seeing the printk's from mce_panic? Why?
How about moving the disabling checking in print_mce? It seems not clean if we disable
the printk recursion checking just around every printk statement.


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