On Wed, Nov 16, 2022 at 05:27:12PM +0106, John Ogness wrote: > This is v5 of a series to prepare for threaded/atomic > printing. v4 is here [0]. This series focuses on reducing the > scope of the BKL console_lock. It achieves this by switching to > SRCU and a dedicated mutex for console list iteration and > modification, respectively. The console_lock will no longer > offer this protection. > > Also, during the review of v2 it came to our attention that > many console drivers are checking CON_ENABLED to see if they > are registered. Because this flag can change without > unregistering and because this flag does not represent an > atomic point when an (un)registration process is complete, > a new console_is_registered() function is introduced. This > function uses the console_list_lock to synchronize with the > (un)registration process to provide a reliable status. > > All users of the console_lock for list iteration have been > modified. For the call sites where the console_lock is still > needed (for other reasons), comments are added to explain > exactly why the console_lock is needed. > > All users of CON_ENABLED for registration status have been > modified to use console_is_registered(). Note that there are > still users of CON_ENABLED, but this is for legitimate purposes > about a registered console being able to print. > > The base commit for this series is from Paul McKenney's RCU tree > and provides an NMI-safe SRCU implementation [1]. Without the > NMI-safe SRCU implementation, this series is not less safe than > mainline. But we will need the NMI-safe SRCU implementation for > atomic consoles anyway, so we might as well get it in > now. Especially since it _does_ increase the reliability for > mainline in the panic path. > > Changes since v4: > > printk: > > - Introduce console_init_seq() to handle the now rather complex > procedure to find an appropriate start sequence number for a > new console upon registration. > > - When registering a non-boot console and boot consoles are > registered, try to flush all the consoles to get the next @seq > value before falling back to use the @seq of the enabled boot > console that is furthest behind. > > - For console_force_preferred_locked(), make the console the > head of the console list. > Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
