linux-kernel - [RFC][PATCHv5 00/13] printk: introduce printing kernel thread

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Message-Id: <20170815025625.1977-1-sergey.senozhatsky@gmail.com>
Date:   Tue, 15 Aug 2017 11:56:12 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     Jan Kara <jack@...e.cz>, Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Eric Biederman <ebiederm@...ssion.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, Pavel Machek <pavel@....cz>,
        Andreas Mohr <andi@...as.de>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: [RFC][PATCHv5 00/13] printk: introduce printing kernel thread

Hello,

        RFC

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

        Offloading threshold is now in "seconds spent in console_unlock()",
not in "lines printed", this lets us to be a little bit more 'watchdog-aware'
in printk. But we still can (and probably must) do better, tho. May be there
will be a new watchdog API some day, so will be able to make better decisions
in printk.

        And a whole bunch of other improvements and tweaks. Like preemption
in console_unlock(), and so on. Any comments and thoughts are appreciated.


v4->v5
-- split some of the patches
-- make offloading time-based (not number of lines printed)
-- move offloading control to per-CPU
-- remove a pessimistic offloading spin from console_unlock()
-- adjust printk_kthread CPU affinity mask
-- disable preemption in console_unlock()
-- always offload printing from user space processes
-- add sync version of emergency_begin API
-- offload from printk_kthread as well, to periodically up() console_sem
-- limit `atomic_print_limit' to `watchdog_thresh'
-- and some other changes...

v3->v4 (Petr, Jan)
-- add syscore notifiers
-- fix 0001 compilation warnings
-- use proper CPU notifiers return values

v2->v3 (Petr, Pavel, Andreas):
-- rework offloading
-- use PM notifiers
-- dropped some patches, etc. etc.

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 (13):
  printk: move printk_pending out of per-cpu
  printk: introduce printing kernel thread
  printk: add sync printk_emergency API
  printk: add enforce_emergency parameter
  printk: enable printk offloading
  printk: register PM notifier
  printk: register syscore notifier
  printk: set watchdog_thresh as maximum value for atomic_print_limit
  printk: add auto-emergency enforcement mechanism
  printk: force printk_kthread to offload printing
  printk: always offload printing from user-space processes
  printk: do not cond_resched() when we can offload
  printk: move offloading logic to per-cpu

 Documentation/admin-guide/kernel-parameters.txt |  17 +
 include/linux/console.h                         |   5 +
 kernel/printk/printk.c                          | 435 ++++++++++++++++++++++--
 3 files changed, 433 insertions(+), 24 deletions(-)

-- 
2.14.1