linux-kernel - [PATCH] printk: tie printk_once / printk_deferred

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Message-ID: <1555121491-31213-1-git-send-email-paul.gortmaker@windriver.com>
Date:   Fri, 12 Apr 2019 22:11:31 -0400
From:   Paul Gortmaker <paul.gortmaker@...driver.com>
To:     <linux-kernel@...r.kernel.org>
CC:     Paul Gortmaker <paul.gortmaker@...driver.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] printk: tie printk_once / printk_deferred_once into .data.once for reset

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 <ak@...ux.intel.com>
Cc: Petr Mladek <pmladek@...e.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.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