linux-kernel - Re: [PATCH] minimize lockdep

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Date:	Wed, 24 Jan 2007 12:55:57 -0500
From:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
To:	Andrew Morton <akpm@...l.org>
Cc:	Greg Kroah-Hartman <gregkh@...e.de>,
	Richard J Moore <richardj_moore@...ibm.com>,
	linux-kernel@...r.kernel.org,
	"Martin J. Bligh" <mbligh@...igh.org>,
	Christoph Hellwig <hch@...radead.org>,
	Douglas Niehaus <niehaus@...s.ku.edu>,
	Ingo Molnar <mingo@...hat.com>, ltt-dev@...fik.org,
	systemtap@...rces.redhat.com, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] minimize lockdep_on/off side-effect

Minimize lockdep_on/off side-effect on irq tracing in vprintk by using
raw_local_irq_save/restore _around_ lockdep_off/on().

It applies on the previous patch. It has the advantage of not losing the IRQ
events coming between the lockdep disabling and the irq disabling.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>

 
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -530,8 +530,8 @@ asmlinkage int vprintk(const char *fmt, va_list args)
 		zap_locks();
 
 	/* This stops the holder of console_sem just where we want him */
+	raw_local_irq_save(flags);
 	lockdep_off();
-	local_irq_save(flags);
 	spin_lock(&logbuf_lock);
 	printk_cpu = smp_processor_id();
 
@@ -640,8 +640,8 @@ asmlinkage int vprintk(const char *fmt, va_list args)
 			console_locked = 0;
 			up(&console_sem);
 		}
-		local_irq_restore(flags);
 		lockdep_on();
+		raw_local_irq_restore(flags);
 	} else {
 		/*
 		 * Someone else owns the drivers.  We drop the spinlock, which
@@ -650,8 +650,8 @@ asmlinkage int vprintk(const char *fmt, va_list args)
 		 */
 		printk_cpu = UINT_MAX;
 		spin_unlock(&logbuf_lock);
-		local_irq_restore(flags);
 		lockdep_on();
+		raw_local_irq_restore(flags);
 	}
 
 	preempt_enable();
-- 
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