linux-kernel - Re: [PATCH] printk: ignore recursion

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Date:	Thu, 24 May 2012 08:38:13 +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>,
	andi@...stfloor.org, Andrew Morton <akpm@...ux-foundation.org>,
	Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH] printk: ignore recursion_bug flag when MCE in progress

On Wed, 2012-05-23 at 12:01 +0200, Borislav Petkov wrote:
> + Tony
> 
> On Wed, May 23, 2012 at 09:58:34AM +0800, ShuoX Liu wrote:
> > From: ShuoX Liu <shuox.liu@...el.com>
> > 
> > When MCE happens in printk, we ignore recursion_bug to make sure
> > some MCE logs printed out. Re-use mce_entry variable.
> > 
> > Signed-off-by: Yanmin Zhang <yanmin_zhang@...ux.intel.com>
> > Signed-off-by: ShuoX Liu <shuox.liu@...el.com>
> > ---
> > I found mce_entry was introduced by commit 553f265f, but it's not
> > used now. Why not removed?
> > ---
> >  arch/x86/include/asm/mce.h       |    2 --
> >  arch/x86/kernel/cpu/mcheck/mce.c |    2 --
> >  include/linux/kernel.h           |    1 +
> >  kernel/printk.c                  |    4 +++-
> >  4 files changed, 4 insertions(+), 5 deletions(-)
> > 
> > diff --git a/arch/x86/include/asm/mce.h b/arch/x86/include/asm/mce.h
> > index 441520e..aeda4cc 100644
> > --- a/arch/x86/include/asm/mce.h
> > +++ b/arch/x86/include/asm/mce.h
> > @@ -187,8 +187,6 @@ int mce_available(struct cpuinfo_x86 *c);
> >  DECLARE_PER_CPU(unsigned, mce_exception_count);
> >  DECLARE_PER_CPU(unsigned, mce_poll_count);
> >  
> > -extern atomic_t mce_entry;
> > -
> >  typedef DECLARE_BITMAP(mce_banks_t, MAX_NR_BANKS);
> >  DECLARE_PER_CPU(mce_banks_t, mce_poll_banks);
> >  
> > diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
> > index 11c9166..6073354 100644
> > --- a/arch/x86/kernel/cpu/mcheck/mce.c
> > +++ b/arch/x86/kernel/cpu/mcheck/mce.c
> > @@ -61,8 +61,6 @@ int mce_disabled __read_mostly;
> >  
> >  #define SPINUNIT 100	/* 100ns */
> >  
> > -atomic_t mce_entry;
> > -
> >  DEFINE_PER_CPU(unsigned, mce_exception_count);
> >  
> >  /*
> > diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> > index 645231c..24af685 100644
> > --- a/include/linux/kernel.h
> > +++ b/include/linux/kernel.h
> > @@ -354,6 +354,7 @@ unsigned long int_sqrt(unsigned long);
> >  extern void bust_spinlocks(int yes);
> >  extern void wake_up_klogd(void);
> >  extern int oops_in_progress;		/* If set, an oops, panic(), BUG() or die() is in progress */
> > +extern atomic_t mce_entry;
> >  extern int panic_timeout;
> >  extern int panic_on_oops;
> >  extern int panic_on_unrecovered_nmi;
> > diff --git a/kernel/printk.c b/kernel/printk.c
> > index 473afdb..2bae087 100644
> > --- a/kernel/printk.c
> > +++ b/kernel/printk.c
> > @@ -79,6 +79,7 @@ int console_printk[4] = {
> >  int oops_in_progress;
> >  EXPORT_SYMBOL(oops_in_progress);
> >  
> > +atomic_t mce_entry;
> >  /*
> >   * console_sem protects the console_drivers list, and also
> >   * provides serialisation for access to the entire console
> > @@ -864,7 +865,8 @@ asmlinkage int vprintk(const char *fmt, va_list args)
> >  		 * recursion and return - but flag the recursion so that
> >  		 * it can be printed at the next appropriate moment:
> >  		 */
> > -		if (!oops_in_progress && !lockdep_recursing(current)) {
> > +		if (!oops_in_progress && !atomic_read(&mce_entry)
> 
> This is leaking x86-specific (MCE) stuff in generic kernel code. I think
> it would be more appropriate to add a in_hw_error() helper or similar
> and define it on each arch. I can very well imagine other architectures
> would like to print hw error info too...
Good idea. We would do so to make it more generic.

Thanks,
Yanmin


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