From: Mathieu Desnoyers 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 Cc: Ingo Molnar Signed-off-by: Andrew Morton --- 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(); _