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

Sergey Senozhatsky
2016-10-19T04:33:36Z

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