The patch titled
order of lockdep off/on in vprintk() should be changed
has been added to the -mm tree. Its filename is
order-of-lockdep-off-on-in-vprintk-should-be-changed.patch
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: order of lockdep off/on in vprintk() should be changed
From: Mathieu Desnoyers <compudj@xxxxxxxxxxxxxxxxxx>
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@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
kernel/printk.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff -puN kernel/printk.c~order-of-lockdep-off-on-in-vprintk-should-be-changed kernel/printk.c
--- a/kernel/printk.c~order-of-lockdep-off-on-in-vprintk-should-be-changed
+++ a/kernel/printk.c
@@ -529,8 +529,8 @@ asmlinkage int vprintk(const char *fmt,
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();
@@ -617,8 +617,8 @@ asmlinkage int vprintk(const char *fmt,
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
@@ -627,8 +627,8 @@ asmlinkage int vprintk(const char *fmt,
*/
printk_cpu = UINT_MAX;
spin_unlock(&logbuf_lock);
- lockdep_on();
local_irq_restore(flags);
+ lockdep_on();
}
preempt_enable();
_
Patches currently in -mm which might be from compudj@xxxxxxxxxxxxxxxxxx are
order-of-lockdep-off-on-in-vprintk-should-be-changed.patch
minimize-lockdep_on-off-side-effect.patch
-
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