Re: [PATCH v2 07/17] debugobjects: Move printk out of db lock critical sections

Sergey Senozhatsky
2018-11-26T04:57:15Z

On (11/23/18 12:48), Petr Mladek wrote:
[..]
> > This should make serial consoles re-entrant.
> > So printk->console_driver_write() hopefully will not deadlock.
>
> Is the re-entrance safe? Some risk might be acceptable in Oops/panic
> situations. It is much less acceptable for random warnings.

Good question.

But what's the alternative? A deadlock in a serial console driver; such
that even panic() is not guaranteed to make through it (at least of now).
debug objects are used from the code which cannot re-entrant console
drivers.

bust_spinlock is called from various paths, not only panic.
git grep bust_spinlocks | wc -l
62

So we already switch to re-entrant consoles (and accept the risks) in
mm/fault.c, kernel/traps.c and so on. Which, I guess, makes us a little
more confident, faults/traps happen often enough.

It seems, that, more or less, serial consoles are ready to handle it.
UART consoles in ->write() callbacks just do a bunch of writel() [for
every char + \r\n].

-ss