From 1fb8915b9876a80f43732980208b39d013f8da9d Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>
Date: Thu, 11 Dec 2014 09:12:01 -0500
Subject: [PATCH] printk: Do not disable preemption for accessing printk_func

As printk_func will either be the default function, or a per_cpu function
for the current CPU, there's no reason to disable preemption to access
it from printk. That's because if the printk_func is not the default
then the caller had better disabled preemption as they were the one to
change it.

Link: http://lkml.kernel.org/r/CA+55aFz5-_LKW4JHEBoWinN9_ouNcGRWAF2FUA35u46FRN-Kxw@mail.gmail.com

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/printk/printk.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 5af2b8bc88f0..9b896e7a50a9 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1859,10 +1859,16 @@ asmlinkage __visible int printk(const char *fmt, ...)
 	int r;
 
 	va_start(args, fmt);
-	preempt_disable();
+
+	/*
+	 * If a caller overrides the per_cpu printk_func, then it needs
+	 * to disable preemption when calling printk(). Otherwise
+	 * the printk_func should be set to the default. No need to
+	 * disable preemption here.
+	 */
 	vprintk_func = this_cpu_read(printk_func);
 	r = vprintk_func(fmt, args);
-	preempt_enable();
+
 	va_end(args);
 
 	return r;