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>

1 files 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;