[RFC][PATCHv2 0/8] printk: introduce printing kernel thread

[Sergey Senozhatsky <sergey.senozhatsky@gmail.com>]

Hello

	RFC

	This patch set adds a printk() kernel thread which lets us to
print kernel messages to the console from a non-atomic/schedule-able
context, avoiding different sort of lockups, stalls, etc.

	The biggest difference compared to v1 is a further expansion of
"switch to old printk() mode", which we now call printk_emergency mode,
annotations (pm, kexec, sysrq).

	We also have a bunch of other ideas to try out/consider (not in
this patch set). E.g. automatic printk_emergency switch on printk_kthread
stalls (when we can't run printk_kthread), moving klogd irq_work out of
per-CPU memory, and so on.

v1->v2:
-- introduce printk_emergency mode and API to switch it on/off
-- move printk_pending out of per-CPU memory
-- add printk emergency_mode sysfs node
-- switch sysrq handlers (some of them) to printk_emergency
-- cleanus/etc.

Sergey Senozhatsky (8):
  printk: move printk_pending out of per-cpu
  printk: introduce printing kernel thread
  printk: offload printing from wake_up_klogd_work_func()
  pm: switch to printk.emergency mode in unsafe places
  sysrq: switch to printk.emergency mode in unsafe places
  kexec: switch to printk.emergency mode in unsafe places
  printk: add printk emergency_mode parameter
  printk: enable printk offloading

 drivers/tty/sysrq.c      |   7 ++
 include/linux/console.h  |   3 +
 kernel/kexec_core.c      |   4 ++
 kernel/power/hibernate.c |   8 +++
 kernel/power/suspend.c   |   4 ++
 kernel/printk/printk.c   | 178 +++++++++++++++++++++++++++++++++++++++++------
 6 files changed, 182 insertions(+), 22 deletions(-)

-- 
2.12.2