Re: [PATCH printk v2 21/38] serial: kgdboc: use srcu console list iterator

[Doug Anderson]

Hi,

On Fri, Oct 21, 2022 at 8:09 AM Petr Mladek <pmladek@xxxxxxxx> wrote:
>
> On Wed 2022-10-19 17:01:43, John Ogness wrote:
> > Use srcu console list iteration for safe console list traversal.
> >
> > Note that configure_kgdboc() still requires the console_lock in
> > order to ensure that no console is in its write() callback when
> > its direct() callback is called. Add comments to clarify this.
>
> s/direct()/device()/
>
> Do you know about such requirements or is it just
> a conservative approach, please?
>
> I ask because the comment in the code says "may assume".
>
>
> Anyway, this would deserve a comment why the SRCU list iteration is
> needed even when console_lock() is needed as well.
>
> The reason is that further patches are going to synchronize
> console_list manipulation with another lock and console_lock()
> will be used only to serialize accessing con->write() callbacks.

I had the same concern. I'll note that at the end of the series the
documentation for console_lock() still says:

 * Acquires a lock which guarantees that the caller has
 * exclusive access to the console system.

That seems to imply (at least to me) that if you're holding
console_lock() there's no need to hold the SRCU lock.

-Doug