Hi, This is v7 of a series to wire up the nbcon consoles so that they actually perform printing using their write_atomic() callback. v6 is here [0]. For information about the motivation of the atomic consoles, please read the cover letter of v1 [1]. The main focus of this series: - For nbcon consoles, always call write_atomic() directly from printk() caller context for the panic CPU. - For nbcon consoles, call write_atomic() when unlocking the console lock. - Only perform the console lock/unlock dance if legacy or boot consoles are registered. - For legacy consoles, if nbcon consoles are registered, do not attempt to print from printk() caller context for the panic CPU until nbcon consoles have had a chance to print the most significant messages. - Mark emergency sections. In these sections, every printk() call will attempt to directly flush to the consoles using the EMERGENCY priority. This series does _not_ include threaded printing or nbcon drivers. Those features will be added in separate follow-up series. The changes since v6: - When a CPU is in an emergency state, printk() calls will now flush directly to all consoles using the EMERGENCY priority. - Remove usage and implementation of nbcon_cpu_emergency_flush(). - Add printk_get_console_flush_type() to query available flush types and use it at all flushing call sites. - In vprintk_emit(), always use nbcon_atomic flushing if it is available. - When exiting nbcon_device_release(), flush using the legacy loop if nbcon_atomic flushing is not available. - In console_flush_on_panic(), make sure nbcon_atomic flushing is allowed before flushing. - In pr_flush(), always take the console_lock because there is no synchronization against register_console() and legacy consoles could register while waiting. - In __wake_up_klogd(), remove check if PENDING_OUTPUT is needed. If PENDING_OUTPUT is set, it is needed. - Rename is_printk_deferred() to is_printk_legacy_deferred(). - Remove nbcon_init(), consolidate it into nbcon_alloc(). - Improve documentation about nbcon owner/waiter matching rules. - Allow nbcon_get_cpu_emergency_nesting() to run without migration disabled. - Clarify that nbcon_get_default_prio() can run without migration disabled. John Ogness [0] https://lore.kernel.org/lkml/20240527063749.391035-1-john.ogness@xxxxxxxxxxxxx [1] https://lore.kernel.org/lkml/20230302195618.156940-1-john.ogness@xxxxxxxxxxxxx John Ogness (30): printk: Add notation to console_srcu locking printk: nbcon: Consolidate alloc() and init() printk: nbcon: Clarify rules of the owner/waiter matching printk: nbcon: Remove return value for write_atomic() printk: nbcon: Add detailed doc for write_atomic() printk: nbcon: Add callbacks to synchronize with driver printk: nbcon: Use driver synchronization while (un)registering serial: core: Provide low-level functions to lock port serial: core: Introduce wrapper to set @uart_port->cons console: Improve console_srcu_read_flags() comments nbcon: Add API to acquire context for non-printing operations serial: core: Acquire nbcon context in port->lock wrapper printk: nbcon: Do not rely on proxy headers printk: Make console_is_usable() available to nbcon.c printk: Let console_is_usable() handle nbcon printk: Add @flags argument for console_is_usable() printk: nbcon: Add helper to assign priority based on CPU state printk: Track registered boot consoles printk: nbcon: Use nbcon consoles in console_flush_all() printk: Add is_printk_legacy_deferred() printk: nbcon: Flush new records on device_release() printk: Flush nbcon consoles first on panic printk: nbcon: Add unsafe flushing on panic printk: Avoid console_lock dance if no legacy or boot consoles printk: Track nbcon consoles printk: Coordinate direct printing in panic printk: Add helper for flush type logic panic: Mark emergency section in oops rcu: Mark emergency sections in rcu stalls lockdep: Mark emergency sections in lockdep splats Petr Mladek (1): printk: Properly deal with nbcon consoles on seq init Sebastian Andrzej Siewior (1): printk: Check printk_deferred_enter()/_exit() usage Thomas Gleixner (3): printk: nbcon: Provide function to flush using write_atomic() printk: nbcon: Implement emergency sections panic: Mark emergency section in warn drivers/tty/serial/8250/8250_core.c | 6 +- drivers/tty/serial/amba-pl011.c | 2 +- drivers/tty/serial/serial_core.c | 16 +- include/linux/console.h | 110 +++++- include/linux/printk.h | 33 +- include/linux/serial_core.h | 117 +++++- kernel/locking/lockdep.c | 83 +++- kernel/panic.c | 9 + kernel/printk/internal.h | 130 ++++++- kernel/printk/nbcon.c | 565 +++++++++++++++++++++++++--- kernel/printk/printk.c | 250 +++++++++--- kernel/printk/printk_ringbuffer.h | 2 + kernel/printk/printk_safe.c | 23 +- kernel/rcu/tree_exp.h | 7 + kernel/rcu/tree_stall.h | 9 + 15 files changed, 1211 insertions(+), 151 deletions(-) base-commit: 8bf100092d60bf586bbc1a3a2cd833bb212d9d53 -- 2.39.2
