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From: Mathieu Desnoyers <compudj@krystal.dyndns.org>
To: Andrew Morton <akpm@osdl.org>
Cc: Greg Kroah-Hartman <gregkh@suse.de>,
	Richard J Moore <richardj_moore@uk.ibm.com>,
	linux-kernel@vger.kernel.org,
	"Martin J. Bligh" <mbligh@mbligh.org>,
	Christoph Hellwig <hch@infradead.org>,
	Douglas Niehaus <niehaus@eecs.ku.edu>,
	Ingo Molnar <mingo@redhat.com>,
	ltt-dev@shafik.org, systemtap@sources.redhat.com,
	Thomas Gleixner <tglx@linutronix.de>
Subject: [PATCH] order of lockdep off/on in vprintk() should be changed
Date: Wed, 24 Jan 2007 12:24:45 -0500	[thread overview]
Message-ID: <20070124172445.GA1145@Krystal> (raw)
In-Reply-To: <20070124165150.GC4979@Krystal>

The order of locking between lockdep_off/on() and local_irq_save/restore() in
vprintk() should be changed.
  
* In kernel/printk.c :

vprintk() does : 

preempt_disable()
local_irq_save()
lockdep_off()
spin_lock(&logbuf_lock)
spin_unlock(&logbuf_lock)
if(!down_trylock(&console_sem))
   up(&console_sem)
lockdep_on()
local_irq_restore() 
preempt_enable()
    
The goals here is to make sure we do not call printk() recursively from
kernel/lockdep.c:__lock_acquire() (called from spin_* and down/up) nor from
kernel/lockdep.c:trace_hardirqs_on/off() (called from local_irq_restore/save).
It can then potentially call printk() through mark_held_locks/mark_lock.
  
It correctly protects against the spin_lock call and the up/down call, but it
does not protect against local_irq_restore. It could cause infinite recursive
printk/trace_hardirqs_on() calls when printk() is called from the
mark_lock() error handing path.

We should change the locking so it becomes correct :

preempt_disable()
lockdep_off()
local_irq_save()
spin_lock(&logbuf_lock)
spin_unlock(&logbuf_lock)
if(!down_trylock(&console_sem))
   up(&console_sem)
local_irq_restore()
lockdep_on()
preempt_enable()


Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.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 */
-	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);
 		}
-		lockdep_on();
 		local_irq_restore(flags);
+		lockdep_on();
 	} 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);
-		lockdep_on();
 		local_irq_restore(flags);
+		lockdep_on();
 	}
 
 	preempt_enable();
-- 
OpenPGP public key:              http://krystal.dyndns.org:8080/key/compudj.gpg
Key fingerprint:     8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68 

  reply	other threads:[~2007-01-24 17:24 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2006-12-20 23:52 [PATCH 0/4] Linux Kernel Markers Mathieu Desnoyers
2006-12-20 23:57 ` [PATCH 1/4] Linux Kernel Markers : Architecture agnostic code Mathieu Desnoyers
2006-12-20 23:59 ` [PATCH 2/4] Linux Kernel Markers : kconfig menus Mathieu Desnoyers
2006-12-21  0:00 ` [PATCH 3/4] Linux Kernel Markers : i386 optimisation Mathieu Desnoyers
2006-12-21  0:01 ` [PATCH 4/4] Linux Kernel Markers : powerpc optimisation Mathieu Desnoyers
2007-01-13  1:33 ` [PATCH 0/4] Linux Kernel Markers Richard J Moore
2007-01-13  5:45   ` Mathieu Desnoyers
2007-01-16 17:41     ` [PATCH 0/4 update] Linux Kernel Markers - i386 : pIII erratum 49 : XMC Mathieu Desnoyers
2007-01-16 18:35       ` Frank Ch. Eigler
2007-01-16 21:27       ` [PATCH 0/4 update] kprobes and traps Mathieu Desnoyers
2007-01-17 12:25         ` S. P. Prasanna
2007-01-16 17:56   ` [PATCH 1/2] lockdep missing barrier() Mathieu Desnoyers
2007-01-24  4:26     ` Andrew Morton
2007-01-24 16:51       ` Mathieu Desnoyers
2007-01-24 17:24         ` Mathieu Desnoyers [this message]
2007-01-24 17:55           ` [PATCH] minimize lockdep_on/off side-effect Mathieu Desnoyers
2007-01-16 17:56   ` [PATCH 2/2] lockdep reentrancy Mathieu Desnoyers
2007-01-24  4:29     ` Andrew Morton
2007-01-24 16:55       ` Mathieu Desnoyers

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