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>
