Commit 1efc5da3 authored by Mathieu Desnoyers's avatar Mathieu Desnoyers Committed by Linus Torvalds

[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: default avatarMathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Acked-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 482a579b
......@@ -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();
......
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