Re: [PATCH printk v2 02/38] printk: Convert console_drivers list to hlist

Greg Kroah-Hartman
2022-10-20T07:43:52Z

On Wed, Oct 19, 2022 at 11:52:53PM +0206, John Ogness wrote:
> On 2022-10-19, Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:
> >> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> >> index e4f1e7478b52..867becc40021 100644
> >> --- a/kernel/printk/printk.c
> >> +++ b/kernel/printk/printk.c
> >> @@ -3229,32 +3244,30 @@ int unregister_console(struct console *console)
> >> if (res > 0)
> >> return 0;
> >>
> >> - res = -ENODEV;
> >> console_lock();
> >> - if (console_drivers == console) {
> >> - console_drivers=console->next;
> >> - res = 0;
> >> - } else {
> >> - for_each_console(con) {
> >> - if (con->next == console) {
> >> - con->next = console->next;
> >> - res = 0;
> >> - break;
> >> - }
> >> - }
> >> +
> >> + /* Disable it unconditionally */
> >> + console->flags &= ~CON_ENABLED;
> >> +
> >> + if (hlist_unhashed(&console->node)) {
> >
> > How can this ever be hit? The console lock is held, so it shouldn't
> > have gone away already. Or am I missing something else here?
>
> Mainline also has this check. I expect it is for the case that some code
> tries to call unregister_console() for a console that is not
> registered.
>
> Since register_console() does not return if it succeeded, I suppose some
> code somewhere my try to unregister without knowing that it never
> registered in the first place.

Ick, ok, that's fine for now.

What a mess, thanks for working to unwind it!

greg k-h