]> pilppa.com Git - linux-2.6-omap-h63xx.git/commit
[PATCH] order of lockdep off/on in vprintk() should be changed
authorMathieu Desnoyers <compudj@krystal.dyndns.org>
Sat, 10 Feb 2007 09:46:29 +0000 (01:46 -0800)
committerLinus Torvalds <torvalds@woody.linux-foundation.org>
Sun, 11 Feb 2007 19:18:06 +0000 (11:18 -0800)
commit1efc5da3cf567d2f6b795f9d2112ed97fec4ee7c
tree25a45ed5a45e5ad54c6264240cd3c55e751858b3
parent482a579b370a0bf924b577efd6c750284a95e0fb
[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>
kernel/printk.c