[PATCH printk v7 00/35] wire up write_atomic() printing

[John Ogness]

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