[PATCH] printk: tie printk_once / printk_deferred_once into .data.once for reset

[Paul Gortmaker]

In commit b1fca27d384e ("kernel debug: support resetting WARN*_ONCE")
we got the opportunity to reset state on the one shot messages,
without having to reboot.

However printk_once (printk_deferred_once) live in a different file
and didn't get the same kind of update/conversion, so they remain
unconditionally one shot, until the system is rebooted.

For example, we currently have:

  sched/rt.c: printk_deferred_once("sched: RT throttling activated\n");

..which could reasonably be tripped as someone is testing and tuning
a new system/workload and their task placements.  For consistency, and
to avoid reboots in the same vein as the original commit, we make these
two instances of _once the same as the WARN*_ONCE instances are.

Cc: Andi Kleen <a...@linux.intel.com>
Cc: Petr Mladek <pmla...@suse.com>
Cc: Sergey Senozhatsky <sergey.senozhat...@gmail.com>
Cc: Steven Rostedt <rost...@goodmis.org>
Cc: Andrew Morton <a...@linux-foundation.org>
Signed-off-by: Paul Gortmaker <paul.gortma...@windriver.com>
---
 Documentation/clearing-warn-once.txt | 2 +-
 include/linux/printk.h               | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/Documentation/clearing-warn-once.txt 
b/Documentation/clearing-warn-once.txt
index 5b1f5d547be1..c68598b31428 100644
--- a/Documentation/clearing-warn-once.txt
+++ b/Documentation/clearing-warn-once.txt
@@ -1,5 +1,5 @@
 
-WARN_ONCE / WARN_ON_ONCE only print a warning once.
+WARN_ONCE / WARN_ON_ONCE / printk_once only emit a message once.
 
 echo 1 > /sys/kernel/debug/clear_warn_once
 
diff --git a/include/linux/printk.h b/include/linux/printk.h
index d7c77ed1a4cb..84ea4d094af3 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -347,7 +347,7 @@ extern int kptr_restrict;
 #ifdef CONFIG_PRINTK
 #define printk_once(fmt, ...)                                  \
 ({                                                             \
-       static bool __print_once __read_mostly;                 \
+       static bool __section(.data.once) __print_once;         \
        bool __ret_print_once = !__print_once;                  \
                                                                \
        if (!__print_once) {                                    \
@@ -358,7 +358,7 @@ extern int kptr_restrict;
 })
 #define printk_deferred_once(fmt, ...)                         \
 ({                                                             \
-       static bool __print_once __read_mostly;                 \
+       static bool __section(.data.once) __print_once;         \
        bool __ret_print_once = !__print_once;                  \
                                                                \
        if (!__print_once) {                                    \
-- 
2.7.4