Re: [RFC][PATCHv3 0/6] printk: use printk_safe to handle printk() recursive calls

[Sergey Senozhatsky]

On (10/19/16 00:40), Sergey Senozhatsky wrote:
[..]
> Deadlock scenarios that printk_safe can handle:
> 
> a) printk recursion from logbuf_lock spin_lock section in printk()
>   printk()
>     raw_spin_lock(&logbuf_lock);
>     WARN_ON(1);
>     raw_spin_unlock(&logbuf_lock);
> 
> b) printk from sem->lock spin_lock section
>   printk()
>     console_trylock()
>       down_trylock()
>         raw_spin_lock_irqsave(&sem->lock, flags);
>         WARN_ON(1);
>         raw_spin_unlock_irqrestore(&sem->lock, flags);
> 
> c) printk from logbuf_lock spin_lock section in console_unlock()
>   printk()
>     console_unlock()
>       raw_spin_lock(&logbuf_lock);
>       WARN_ON(1);
>       raw_spin_unlock(&logbuf_lock);
> 
> d) printk from ->pi_lock from semaphore up
>   printk()
>     console_unlock()
>       up()
>         try_to_wake_up()
>           raw_spin_lock_irqsave(&p->pi_lock, flags);
>           WARN_ON(1);
>           raw_spin_unlock_irqrestore(&p->pi_lock, flags);

and

e) anything from call_console_drivers() should be fine as well.
   console_unlock() big printing loop is covered by printk_safe,
   need to protect console_cont_flush()->call_console_drivers().

   so printk "direct path" seems to be safe now:

   printk -> .. -> console_unlock() -> call_console_drivers() -> serial_console_write()

   anything that is "indirect" is not covered in this patch set.


	-ss