[3.19.y-ckt stable] Patch "printk: help pr_debug and pr_devel to optimize out arguments" has been added to the 3.19.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    printk: help pr_debug and pr_devel to optimize out arguments

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-ckt14.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From e51935904962ff61aa95b6f61066ff4dda2ed6ad Mon Sep 17 00:00:00 2001
From: Aaron Conole <aconole at redhat.com>
Date: Fri, 15 Jan 2016 16:59:12 -0800
Subject: printk: help pr_debug and pr_devel to optimize out arguments

commit fe22cd9b7c980b8b948ec85f034a8668c57ec867 upstream.

Currently, pr_debug and pr_devel will not elide function call arguments
appearing in calls to the no_printk for these macros.  This is because
all side effects must be honored before proceeding to the 0-value
assignment in no_printk.

The behavior is contrary to documentation found in the CodingStyle and
the header file where these functions are declared.

This patch corrects that behavior by shunting out the call to no_printk
completely.  The format string is still checked by gcc for correctness,
but no code seems to be emitted in common cases.

[akpm at linux-foundation.org: remove braces, per Joe]
Fixes: 5264f2f75d86 ("include/linux/printk.h: use and neaten no_printk")
Signed-off-by: Aaron Conole <aconole at redhat.com>
Reported-by: Dmitry Vyukov <dvyukov at google.com>
Cc: Joe Perches <joe at perches.com>
Cc: Jason Baron <jbaron at akamai.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>

Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 include/linux/printk.h | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/linux/printk.h b/include/linux/printk.h
index 4d5bf57..20370e66 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -104,13 +104,13 @@ struct va_format {

 /*
  * Dummy printk for disabled debugging statements to use whilst maintaining
- * gcc's format and side-effect checking.
+ * gcc's format checking.
  */
-static inline __printf(1, 2)
-int no_printk(const char *fmt, ...)
-{
-	return 0;
-}
+#define no_printk(fmt, ...)			\
+do {						\
+	if (0)					\
+		printk(fmt, ##__VA_ARGS__);	\
+} while (0)

 #ifdef CONFIG_EARLY_PRINTK
 extern asmlinkage __printf(1, 2)
--
1.9.1