linux-kernel - [RFC] [PATCH] printk: Don't emit console_cpu_notify() for CPU

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Message-Id: <1321582764-22218-1-git-send-email-yong.zhang0@gmail.com>
Date:	Fri, 18 Nov 2011 10:19:24 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, James Morris <jmorris@...ei.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Kevin Cernekee <cernekee@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: [RFC] [PATCH] printk: Don't emit console_cpu_notify() for CPU_DYING

When running -rt, I got some warning when doing cpu hotplug,
for details please check:
http://marc.info/?l=linux-kernel&m=132143661616297&w=2

But seems the problem also exists in mainline, a typical
scenario is:

        CPU A                           CPU B

doing printk with console_sem held
                                take_cpu_down();
                                  cpu_notify(CPU_DYING);
                                    console_cpu_notify();
                                      console_lock();
                                        down(&console_sem);
                                          *BANG*
  up(&console_sem);


Signed-off-by: Yong Zhang <yong.zhang0@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: James Morris <jmorris@...ei.org>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Kevin Cernekee <cernekee@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Steven Rostedt <rostedt@...dmis.org>
---
 kernel/printk.c |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)

diff --git a/kernel/printk.c b/kernel/printk.c
index 535bc3b..ba0393e 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -1223,7 +1223,6 @@ static int __cpuinit console_cpu_notify(struct notifier_block *self,
 	switch (action) {
 	case CPU_ONLINE:
 	case CPU_DEAD:
-	case CPU_DYING:
 	case CPU_DOWN_FAILED:
 	case CPU_UP_CANCELED:
 		console_lock();
-- 
1.7.5.4

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