linux-kernel - Re: [debug patch] printk: Add a printk killswitch to robustify NMI watchdog messages

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Date:	Mon, 6 Jun 2011 15:21:42 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Arne Jansen <lists@...-jansens.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	efault@....de, npiggin@...nel.dk, akpm@...ux-foundation.org,
	frank.rowand@...sony.com, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org
Subject: Re: [debug patch] printk: Add a printk killswitch to robustify NMI
 watchdog messages


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Mon, 2011-06-06 at 15:10 +0200, Ingo Molnar wrote:
> 
> 
> > diff --git a/kernel/printk.c b/kernel/printk.c
> > index 3518539..1b9d2be 100644
> > --- a/kernel/printk.c
> > +++ b/kernel/printk.c
> > @@ -859,7 +859,6 @@ asmlinkage int vprintk(const char *fmt, va_list args)
> >  		zap_locks();
> >  	}
> >  
> > -	lockdep_off();
> 
> At the very least you should also do: s/raw_local_irq_/local_irq/ on
> this function.

Right, i've also removed the preempt_disable()/enable() pair - that 
looks superfluous.

Updated patch below - still untested.

Thanks,

	Ingo

---
 kernel/printk.c |   10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

Index: tip/kernel/printk.c
===================================================================
--- tip.orig/kernel/printk.c
+++ tip/kernel/printk.c
@@ -836,9 +836,8 @@ asmlinkage int vprintk(const char *fmt, 
 	boot_delay_msec();
 	printk_delay();
 
-	preempt_disable();
 	/* This stops the holder of console_sem just where we want him */
-	raw_local_irq_save(flags);
+	local_irq_save(flags);
 	this_cpu = smp_processor_id();
 
 	/*
@@ -859,7 +858,6 @@ asmlinkage int vprintk(const char *fmt, 
 		zap_locks();
 	}
 
-	lockdep_off();
 	spin_lock(&logbuf_lock);
 	printk_cpu = this_cpu;
 
@@ -947,7 +945,7 @@ asmlinkage int vprintk(const char *fmt, 
 	 * Try to acquire and then immediately release the
 	 * console semaphore. The release will do all the
 	 * actual magic (print out buffers, wake up klogd,
-	 * etc). 
+	 * etc).
 	 *
 	 * The console_trylock_for_printk() function
 	 * will release 'logbuf_lock' regardless of whether it
@@ -956,11 +954,9 @@ asmlinkage int vprintk(const char *fmt, 
 	if (console_trylock_for_printk(this_cpu))
 		console_unlock();
 
-	lockdep_on();
 out_restore_irqs:
-	raw_local_irq_restore(flags);
+	local_irq_restore(flags);
 
-	preempt_enable();
 	return printed_len;
 }
 EXPORT_SYMBOL(printk);
--
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