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[PATCHv6 0/7] printk: use printk_safe to handle printk() recursive calls

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Hello,

        This patch set extends a lock-less NMI per-cpu buffers idea to
handle recursive printk() calls. The basic mechanism is pretty much the
same -- at the beginning of a deadlock-prone section we switch to lock-less
printk callback, and return back to a default printk implementation at the
end; the messages are getting flushed to a logbuf buffer from a safer
context.

Deadlock scenarios that printk_safe can handle:

a) printk recursion from logbuf_lock spin_lock section in printk()
  printk()
    raw_spin_lock(&logbuf_lock);
    WARN_ON(1);
    raw_spin_unlock(&logbuf_lock);

b) printk from sem->lock spin_lock section
  printk()
    console_trylock()
      down_trylock()
        raw_spin_lock_irqsave(&sem->lock, flags);
        WARN_ON(1);
        raw_spin_unlock_irqrestore(&sem->lock, flags);

c) printk from logbuf_lock spin_lock section in console_unlock()
  printk()
    console_unlock()
      raw_spin_lock(&logbuf_lock);
      WARN_ON(1);
      raw_spin_unlock(&logbuf_lock);

d) printk from ->pi_lock from semaphore up
  printk()
    console_unlock()
      up()
        try_to_wake_up()
          raw_spin_lock_irqsave(&p->pi_lock, flags);
          WARN_ON(1);
          raw_spin_unlock_irqrestore(&p->pi_lock, flags);

e) printk from console_cont_flush() /*and down the call chain */
  printk()
    console_unlock()
      call_console_drivers()
       ...
          WARN_ON(1);

v6:
-- re-based
-- addressed Petr's review (added comments; moved lost accounting to seq buf)

v5:
-- some style clean-ups and renamings (Petr)
-- use deferred printk when flush nmi/safe messages (Petr)

v4:
-- addressed Steven's review points
-- use printk_safe in console_cont_flush()

v3: (review by Petr)
-- renamed to printk_safe
-- !NMI config build fix
-- report lost messages for both printk_sae and printk_nmi
-- dropped recursion reporting patch
-- etc.

v2:
-- fix build error on !NMI configs, reported by Fengguang
-- reworked the series based on Petr's feedback
-- added a new patch to drop zap_locks()

Sergey Senozhatsky (7):
  printk: use vprintk_func in vprintk()
  printk: rename nmi.c and exported api
  printk: introduce per-cpu safe_print seq buffer
  printk: always use deferred printk when flush printk_safe lines
  printk: report lost messages in printk safe/nmi contexts
  printk: use printk_safe buffers in printk
  printk: remove zap_locks() function

 arch/arm/kernel/smp.c                  |   4 +-
 include/linux/hardirq.h                |   4 +-
 include/linux/printk.h                 |  29 +++--
 init/Kconfig                           |  16 +--
 init/main.c                            |   2 +-
 kernel/kexec_core.c                    |   2 +-
 kernel/panic.c                         |   4 +-
 kernel/printk/Makefile                 |   2 +-
 kernel/printk/internal.h               |  63 +++++-----
 kernel/printk/printk.c                 | 116 +++++-------------
 kernel/printk/{nmi.c => printk_safe.c} | 216 +++++++++++++++++++++++----------
 lib/nmi_backtrace.c                    |   2 +-
 12 files changed, 245 insertions(+), 215 deletions(-)
 rename kernel/printk/{nmi.c => printk_safe.c} (53%)

-- 
2.11.0

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[PATCHv6 0/7] printk: use printk_safe to handle printk() recursive calls Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-12-21 15:40 +0100
  [PATCHv6 6/7] printk: use printk_safe buffers in printk Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-12-21 15:40 +0100
    Re: [PATCHv6 6/7] printk: use printk_safe buffers in printk Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-12-22 06:40 +0100
      Re: [PATCHv6 6/7] printk: use printk_safe buffers in printk Petr Mladek <pmladek@suse.com> - 2016-12-22 18:20 +0100
        Re: [PATCHv6 6/7] printk: use printk_safe buffers in printk Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-12-23 02:50 +0100
          Re: [PATCHv6 6/7] printk: use printk_safe buffers in printk Petr Mladek <pmladek@suse.com> - 2016-12-23 11:00 +0100
  [PATCHv6 7/7] printk: remove zap_locks() function Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-12-21 15:40 +0100
  [PATCHv6 2/7] printk: rename nmi.c and exported api Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-12-21 15:40 +0100
    Re: [PATCHv6 2/7] printk: rename nmi.c and exported api Linus Torvalds <torvalds@linux-foundation.org> - 2016-12-21 20:50 +0100
      Re: [PATCHv6 2/7] printk: rename nmi.c and exported api Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-12-22 02:20 +0100
  [PATCHv6 1/7] printk: use vprintk_func in vprintk() Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-12-21 15:40 +0100
  [PATCHv6 4/7] printk: always use deferred printk when flush printk_safe lines Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-12-21 15:50 +0100
  [PATCHv6 3/7] printk: introduce per-cpu safe_print seq buffer Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-12-21 15:50 +0100
    Re: [PATCHv6 3/7] printk: introduce per-cpu safe_print seq buffer Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-12-22 02:20 +0100
      Re: [PATCHv6 3/7] printk: introduce per-cpu safe_print seq buffer Petr Mladek <pmladek@suse.com> - 2016-12-22 17:40 +0100

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