Hi, This is v3 of a series to implement threaded console printing as well as some other minor pieces (such as proc and sysfs support). v2 is here [0]. For information about the motivation of the nbcon consoles, please read the cover letter of the original v1 [1]. This series provides the remaining pieces of the printk rework. All other components are either already mainline or are currently in linux-next. In particular this series does: - Implement dedicated printing threads per nbcon console. - Implement forced threading of legacy consoles for PREEMPT_RT. - Implement nbcon support for proc and sysfs console-related files. - Provide a new helper function nbcon_reacquire_nobuf() to allow nbcon console drivers to reacquire ownership. Note that this series does *not* provide an nbcon console driver. That will come in a follow-up series. Here are the main changes since v2: - Drop the patch for "threadprintk" boot arg for !PREEMPT_RT. - Rename variables and functions: force_printkthreads() -> force_legacy_kthread() nbcon_reacquire() -> nbcon_reacquire_nobuf() nbcon_wake_threads() -> nbcon_wake_kthreads() nbcon_legacy_kthread_func() -> legacy_kthread_func() wake_up_legacy_kthread() -> legacy_kthread_wake() @printk_threads_enabled -> @printk_kthreads_running @nbcon_legacy_kthread -> @printk_legacy_kthread - Introduce @printk_kthreads_ready to flag when it is allowed to create kthreads. - Rename lockdep map functions with updated comments to hopefully better clarify their purpose. - The write_thread() callback is now mandatory. write_atomic() remains optional. (This also simplifies the changes to drivers/tty/tty_io.c and fs/proc/consoles.c.) - Merge nbcon_init() into nbcon_alloc(). This simplifies the rules and more closely resembles the legacy registration. - Introduce struct console_flush_type to inform which flushing type to use. - Introduce flushing type macro printk_get_console_flush_type() for non-emergency CPU states. - Introduce flushing type macro printk_get_emergency_console_flush_type() for emergency CPU states. - Remove @printing_via_unlock macro since there is now the flushing type macros. - Replace _all_ flushing decisions with calls to new flushing type macros. - Introduce helper function nbcon_write_context_set_buf() for setting up the write context for nbcon printers. - In nbcon and legacy kthread functions, do not check for spurious signals. - In nbcon_kthread_func(), check for kthread_should_stop() inside the printing loop. - In nbcon_kthread_func(), add cond_resched() inside the printing loop. - In rcuwait_has_sleeper(), avoid unnecessary RCU dereference. - In nbcon_wake_kthreads(), do not try to wake if kthreads are not fully available. - In nbcon_legacy_emit_next_record(), split the atomic/thread cases before and after printing. - Use suggested alternative implementation for console_prepend_message(). - Move all functions to start/stop kthreads into printk.c. - Introduce printk_kthreads_check_locked() to start/stop kthreads if needed when the console list has changed. - Unregister nbcon console if the related kthread printer cannot be created. - On failure to start the legacy kthread, unregister all legacy consoles. - If all legacy consoles unregister, stop legacy kthread. - If all nbcon consoles unregister, clear @nbcon_kthreads_running. - On shutdown, clear @nbcon_kthreads_running. - In unregister_console_locked(), flush the console before unregistering. - Let pr_flush() fail if called _very_ early. - Do not wake nbcon kthreads in printk_trigger_flush(). - In console_try_replay_all(), add support for the legacy kthread. - Refactor the series to hopefully provide a cleaner transition to the final desired stand. - Split -20 nice for kthreads into a separate patch. - Rewrite many comments and commit messages as requested. John Ogness [0] https://lore.kernel.org/lkml/20240603232453.33992-1-john.ogness@xxxxxxxxxxxxx [1] https://lore.kernel.org/lkml/20230302195618.156940-1-john.ogness@xxxxxxxxxxxxx John Ogness (18): printk: nbcon: Clarify nbcon_get_default_prio() context printk: nbcon: Consolidate alloc() and init() printk: nbcon: Add function for printers to reacquire ownership printk: nbcon: Clarify rules of the owner/waiter matching printk: Fail pr_flush() if before SYSTEM_SCHEDULING printk: Flush console on unregister_console() printk: Add helpers for flush type logic printk: nbcon: Add context to usable() and emit() printk: nbcon: Use thread callback if in task context for legacy printk: nbcon: Rely on kthreads for normal operation printk: Provide helper for message prepending printk: nbcon: Show replay message on takeover proc: consoles: Add notation to c_start/c_stop proc: Add nbcon support for /proc/consoles tty: sysfs: Add nbcon support for 'active' printk: Implement legacy printer kthread for PREEMPT_RT printk: nbcon: Assign nice -20 for printing threads printk: Avoid false positive lockdep report for legacy printing Thomas Gleixner (1): printk: nbcon: Introduce printer kthreads drivers/tty/tty_io.c | 2 +- fs/proc/consoles.c | 7 +- include/linux/console.h | 50 +++- kernel/printk/internal.h | 159 ++++++++++- kernel/printk/nbcon.c | 530 ++++++++++++++++++++++++++++++----- kernel/printk/printk.c | 588 +++++++++++++++++++++++++++++++-------- 6 files changed, 1137 insertions(+), 199 deletions(-) base-commit: b18703ea7157f62f02eb0ceb11f6fa0138e90adc -- 2.39.2
