linux-kernel - [RFC PATCH 1/3] printk: convert ignore_loglevel to atomic

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Date:   Sun, 15 Mar 2020 18:09:01 +0100
From:   Eugeniu Rosca <roscaeugeniu@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Jisheng Zhang <Jisheng.Zhang@...aptics.com>,
        Valdis Kletnieks <valdis.kletnieks@...edu>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Andrew Gabbasov <andrew_gabbasov@...tor.com>,
        Dirk Behme <dirk.behme@...bosch.com>,
        Eugeniu Rosca <erosca@...adit-jv.com>
Subject: [RFC PATCH 1/3] printk: convert ignore_loglevel to atomic_t

Prepare for using the 'ignore_loglevel' variable as a lockless and SMP
safe vehicle to turn console verbosity on and off in error paths which
usually (but not necessarily) end up with panic (configurable via
user-selectable knobs).

No functional change intended. Tested on R-Car H3ULCB.

Cc: Petr Mladek <pmladek@...e.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Eugeniu Rosca <erosca@...adit-jv.com>
---
 kernel/printk/printk.c | 30 ++++++++++++++++++++++++++----
 1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index fada22dc4ab6..d2c75955a0d7 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1181,24 +1181,46 @@ void __init setup_log_buf(int early)
 		free, (free * 100) / __LOG_BUF_LEN);
 }
 
-static bool __read_mostly ignore_loglevel;
+atomic_t __read_mostly ignore_loglevel = ATOMIC_INIT(0);
 
 static int __init ignore_loglevel_setup(char *str)
 {
-	ignore_loglevel = true;
+	atomic_set(&ignore_loglevel, 1);
 	pr_info("debug: ignoring loglevel setting.\n");
 
 	return 0;
 }
 
+static int kparam_set_atomic(const char *val, const struct kernel_param *kp)
+{
+	if (param_set_bool(val, kp))
+		return -EINVAL;
+
+	atomic_set(&ignore_loglevel, *(bool *)kp->arg ? 1 : 0);
+
+	return 0;
+}
+
+static int kparam_get_atomic(char *val, const struct kernel_param *kp)
+{
+	return sprintf(val, "%c\n", atomic_read(&ignore_loglevel) ? 'Y' : 'N');
+}
+
+static const struct kernel_param_ops kparam_ops = {
+	.set = kparam_set_atomic,
+	.get = kparam_get_atomic,
+};
+
+static int kparam_buf;
+
 early_param("ignore_loglevel", ignore_loglevel_setup);
-module_param(ignore_loglevel, bool, S_IRUGO | S_IWUSR);
+module_param_cb(ignore_loglevel, &kparam_ops, &kparam_buf, 0644);
 MODULE_PARM_DESC(ignore_loglevel,
 		 "ignore loglevel setting (prints all kernel messages to the console)");
 
 static bool suppress_message_printing(int level)
 {
-	return (level >= console_loglevel && !ignore_loglevel);
+	return (level >= console_loglevel && !atomic_read(&ignore_loglevel));
 }
 
 #ifdef CONFIG_BOOT_PRINTK_DELAY
-- 
2.25.0