On Thu 2023-03-02 21:02:05, John Ogness wrote: > From: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > > The current console/printk subsystem is protected by a Big Kernel Lock, > (aka console_lock) which has ill defined semantics and is more or less > stateless. This puts severe limitations on the console subsystem and > makes forced takeover and output in emergency and panic situations a > fragile endavour which is based on try and pray. > > The goal of non-BKL consoles is to break out of the console lock jail > and to provide a new infrastructure that avoids the pitfalls and > allows console drivers to be gradually converted over. > > --- a/kernel/printk/printk.c > +++ b/kernel/printk/printk.c > @@ -3472,6 +3492,14 @@ void register_console(struct console *newcon) > newcon->dropped = 0; > console_init_seq(newcon, bootcon_registered); > > + if (!(newcon->flags & CON_NO_BKL)) > + have_bkl_console = true; We never clear this value even when the console gets unregistered. > + else > + cons_nobkl_init(newcon); > + > + if (newcon->flags & CON_BOOT) > + have_boot_console = true; > + > /* > * Put this console in the list - keep the > * preferred driver at the head of the list. > @@ -3515,6 +3543,9 @@ void register_console(struct console *newcon) > if (con->flags & CON_BOOT) > unregister_console_locked(con); > } > + > + /* All boot consoles have been unregistered. */ > + have_boot_console = false; The boot consoles can be removed also by printk_late_init(). I would prefer to make this more error-proof and update both have_bkl_console and have_boot_console in unregister_console(). A solution would be to use a reference counter instead of the boolean. I am not sure if it is worth it. But it seems that refcount_read() is just simple atomic read, aka READ_ONCE(). > } > unlock: > console_list_unlock(); Best Regards, Petr
