• Mathieu Desnoyers's avatar
    [PATCH] order of lockdep off/on in vprintk() should be changed · 1efc5da3
    Mathieu Desnoyers authored
    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>
    1efc5da3
printk.c 28.1 KB