linux-kernel - [PATCH v2 0/3] printk: Deadlock in NMI regression

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Date:   Wed, 27 Jun 2018 16:08:14 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Petr Mladek <pmladek@...e.com>
Subject: [PATCH v2 0/3] printk: Deadlock in NMI regression

The commit 719f6a7040f1bdaf96 ("printk: Use the main logbuf in NMI
when logbuf_lock is available") brought back the possible deadlocks
in printk() and NMI.

This is rework of the proposed fix, see
https://lkml.kernel.org/r/20180606111557.xzs6l3lkvg7lq3ts@pathway.suse.cz

I realized that we could rather easily move the check to vprintk_func()
and still avoid any race. I believe that this is a win-win solution.


Changes against v1:

  + Move the check from vprintk_emit() to vprintk_func()
  + More straightforward commit message
  + Fix build with CONFIG_PRINTK_NMI disabled


Petr Mladek (3):
  printk: Split the code for storing a message into the log buffer
  printk: Create helper function to queue deferred console handling
  printk/nmi: Prevent deadlock when accessing the main log buffer in NMI

 include/linux/printk.h      |  4 ++++
 kernel/printk/internal.h    |  9 ++++++-
 kernel/printk/printk.c      | 57 +++++++++++++++++++++++++++-----------------
 kernel/printk/printk_safe.c | 58 +++++++++++++++++++++++++++++----------------
 kernel/trace/trace.c        |  4 +++-
 lib/nmi_backtrace.c         |  3 ---
 6 files changed, 87 insertions(+), 48 deletions(-)

-- 
2.13.7