On Thu 2022-11-10 17:09:12, John Ogness wrote:
> On 2022-11-10, Petr Mladek <pmladek@xxxxxxxx> wrote:
> >> +void console_force_preferred_locked(struct console *con)
> >> +{
> >> + struct console *cur_pref_con;
> >> +
> >> + if (!console_is_registered_locked(con))
> >> + return;
> >> +
> >> + cur_pref_con = console_first();
> >> +
> >> + /* Already preferred? */
> >> + if (cur_pref_con == con)
> >> + return;
> >> +
> >> + hlist_del_init_rcu(&con->node);
> >
> > We actually should re-initialize the node only after all existing
> > console list walks are finished. Se we should use here:
> >
> > hlist_del_rcu(&con->node);
>
> hlist_del_init_rcu() only re-initializes @pprev pointer.
Ah, I was not aware of it.
> But maybe you
> are concerned that there is a window where list_unhashed() becomes true?
> I agree that it should be changed to hlist_del_rcu() because there
> should not be a window where this console appears unregistered.
Makes sense.
> >> + /* Only the new head can have CON_CONSDEV set. */
> >> + WRITE_ONCE(cur_pref_con->flags, cur_pref_con->flags & ~CON_CONSDEV);
> >
> > As mentioned in the reply for 7th patch, I would prefer to hide this
> > WRITE_ONCE into a wrapper, e.g. console_set_flag(). It might also
> > check that the console_list_lock is taken...
>
> Agreed. For v4 it will become:
>
> console_srcu_write_flags(cur_pref_con->flags & ~CON_CONSDEV);
I am happy that your are going to introduce an API for this.
Just to be sure. The _srcu_ in the name means that the write
will use WRITE_ONCE() so that it can be read safely in SRCU
context using READ_ONCE(). Do I get it correctly, please?
I expect that the counter part will be console_srcu_read_flags().
I like the name. It is better than _unsafe_ that I proposed earlier.
Best Regards,
Petr
