From: Mathieu Desnoyers <compudj@krystal.dyndns.org>
Date: Sat, 10 Feb 2007 09:46:29 +0000 (-0800)
Subject: [PATCH] order of lockdep off/on in vprintk() should be changed
X-Git-Tag: v2.6.21-rc1~274^2~256
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1efc5da3cf567d2f6b795f9d2112ed97fec4ee7c;p=linux-2.6

[PATCH] order of lockdep off/on in vprintk() should be changed

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>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff --git a/kernel/printk.c b/kernel/printk.c
index 4da26b0679..0c151877ff 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -529,7 +529,7 @@ 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);
+	raw_local_irq_save(flags);
 	lockdep_off();
 	spin_lock(&logbuf_lock);
 	printk_cpu = smp_processor_id();
@@ -618,7 +618,7 @@ asmlinkage int vprintk(const char *fmt, va_list args)
 			up(&console_sem);
 		}
 		lockdep_on();
-		local_irq_restore(flags);
+		raw_local_irq_restore(flags);
 	} else {
 		/*
 		 * Someone else owns the drivers.  We drop the spinlock, which
@@ -628,7 +628,7 @@ asmlinkage int vprintk(const char *fmt, va_list args)
 		printk_cpu = UINT_MAX;
 		spin_unlock(&logbuf_lock);
 		lockdep_on();
-		local_irq_restore(flags);
+		raw_local_irq_restore(flags);
 	}
 
 	preempt_enable();